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1
GRAFT COPOLYMERS OF NYLONS
by
Hamid Akhavan Kashani, B.Sc., M.Sc.
June 1976
A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College.
Department of Chemistry, Imperial College,
London, S.W.7.
2
TO MY MOTHER
3
ABSTRACT
Using a specially designed reactive vessel,
solutions of sodium in liquid ammonia have been used
to metalate heterogeneously Nylon 66 [Poly(hexamethylene
adipamide)] and the aromatic nylon, Nomex [Poly(meta
phenylene iso phthalamide)]. Nomex has also been
metalated by sodium naphthalene. The end of each
metalation reaction was denoted by the disappearance
of the colour of the metalating reagents. Using the
metalated polymers, various graft copolymers were
prepared in heterogeneous media by anionic techniques.
A N-benzyl substituted derivative was also prepared.
Degradation of the polyamide during metalation under
the experimental conditions employed, was negligible.
Poly(hexamethylene adipamide-g-ethylene-oxide)
was prepared anionically in a heterogeneous medium.
The percentage of grafting was determined by the
increase in weight, nitrogen microanalysis and titration
of the grafted poly(ethylene-oxide). The relationship
between the degree of metalation and both the percentage
of grafting and solubility of the graft copolymer was
studied. The variation in the glass transition
temperature of the graft copolymer with the percentage
4
of grafting was examined. Measurement of the glass
transition temperature for Nylon 66-g-PEO indicated
that phase separation occurred. The changes in
crystallinity of Nylon 66 produced by precipitation
from a formic acid solution by addition of aqueous
methanol was studied using X-ray diffraction methods
and thermal analysis. The solution properties of
the graft copolymer were studied by viscometric
techniques. Poly(hexamethylene adipamide-g-acrylonitrile)
was prepared and some of its properties were studied.
The partially substituted N-benzyl derivative of
Poly(meta Phenylene-iso Phthalamide) and.Poly(meta phenylene-
iso phthalamide-g-acrylonitrile) were prepared and some of
its properties were examined. The influence of the
heterogeneous reaction medium on each of the products was
investigated.
N-chloro Nylon 66 and Nomex were also synthesized
and the reaction between living poly(ethylene oxide) and
N-methyl pyrrolidone was investigated. An unsuccessful
attempt was made to prepare poly(hexamethylene adipamide-
g-styrene) and poly(meta phenylene-iso phthalamide-g-
ethylene oxide).
5
ACKNOWLEDGEMENTS
I would like to express my gratitude to my
supervisors, Dr. M.H. George and Dr. J.A. Barrie
for their help and encouragement during this work.
I wish to thank the following for their various
assistance:-
Dr. R.S. Osborn for X-Ray Diffraction
Dr. I.S. Kerr for optical microscope
Dr. D. Evans for showing interest in this work and consultations
Mr. N.R.S. Sheppard and Mr. A. Sheer for assistance with characterisation techniques in the polymer laboratory
Mr. H. Maybod and Mr. I. Rezaian for showing interest in this work and co-operation
The technical staff of the Chemistry Department of Imperial College.
6
CONTENTS
Page
ABSTRACT 3
ACKNOWLEDGMENT 5
CHAPTER 1
SYNTHESIS OF BLOCK COPOLYMERS GRAFT COPOLYMERS AND BRANCHED HOMOPOLYMERS 16
Introduction 16
1.2. Summary of Methods of Synthesis of Sequential Polymers 18
1.2.1. Free Radical Mechanisms 18
(a) Chemical Methods
(b) Photolytic Methods
(c) High Energy Irradiation Techniques
(d) Mechanochemical Methods
1.2.2. Ionic Mechanisms 18
(a) Anionic Methods
(b) Cationic Mechanisms
1.3. Free Radical Mechanisms 18
1.3.1. Synthesis by Free Radicals: Chemical Methods 19
(a) Chain Transfer to Polymers 19
(b) Reactions of Reactive Groups in the Chain 21
(i) Unsaturation in the Chain 22
(ii) Peroxide Groups 22
(iii) Diazo Groups 24
(iv) Macromolecular Redox Initiators 25
7
Page
1.3.2. Photolytic Methods 26
(a) Direct Method 26
(b) Indirect Method 28
1.3.3. High Energy Irradiation Methods 29
(a) Direct Mutual Irradiation 30 Technique
(b) Preirradiation Technique 32
1.3.4. Mechanochemical Methods 34
1.4. Synthesis by Ionic Methods 35
1.4.1. Synthesis by Anionic Methods 36
1.4.2. The Application of Anionic Processes to Block Copolymer Synthesis 37
(a) General Consideration 37
(b) Coupling Reactions 37
1.5. Graft Copolymers 42
1.5.1. Grafting of End Functional Polymers onto Polymer Backbones 43
1.5.2. Generation of Anions on Polymer Backbones 45
1.6. Co-ordinative Methods 48
1.7. Ring Opening 49
1.8. Branched Homopolymers 50
8
Page
1.8.1. Comb-Like Polymers 52
(a) Coupling Method 52
(b) Deactivation Method 53
1.8.2. Star-Shaped Polymers 54
(aL Preparation of Star-Shaped Polymers by Coupling 54
(b) By Block Copolymerization 55
CHAPTER 2 BASIC CHEMISTRY OF AMIDES 57
2.1. Introduction 57
2.1.1. Methods of Preparation 58
2.1.2. Basicity and Acidity of Amides 59
2.1.3. Hydrogen Bonding, 62
2.1.4. Alkylation of Amides 62
2.1.5. Photochemical Reactions of Amides 65
(a) Photolysis of Amides , 65
(b) Photoamidation 66
(c) Photooxidation of Amides 67
2.1.6. Radiation Chemistry of Amides 68
2.1.7. N-Chlorination of Amides 68
9
Page
2.1.8. Rearrangement of N-Chloroamides 71
2.1.9. Sodium in Ammonia 71
CHAPTER 3 REVIEW OF PREVIOUS WORK 75
3.1. Introduction 75
3.1.2. Nylon Copolymers 75
3.1.3. Reactivity of Nylons 76
3.1.4. Nitrogen Substituted Nylons 77
3.1.5. Graft Copolymers of Nylons 83
(A) Polycondensation 83
(B) Graft Copolymerization Through Radical Mechanism 87
(a) /5, electron, u.v. irradiation and electric discharge 87
(b) Chemical Methods 94
(C) Ionic Synthesis 97
CHAPTER 4 EXPERIMENTAL 103
4.1. Apparatus 103
4.1.1. The High Vacuum Line 103
4.1.2. Metalation Vessel 103
4.1.3. Thermal Analyser 104
10
4.1.4.
4.1.5.
4.1.6.
IR Spectrophotometer
Centrifuge
Apparatus for the Determination of Polyethylene Oxide
Page
104
105
105
4.1.7. Viscometer 105
4.2. Purification and Preparation of Reagents 105
4.2.1. Nylon 66 105
4.2.2. Tetrahydrofuran 106
4.2.3. Ethylene Oxide 107
4.2.4. Sodium 107
4.2.5. Cumyl Potassium 108
4.2.6. Styrene 108
4.2.7. Ammonia 109
4.2.8. Potassium Bromide 109
4.2.9. Acrylonitrile 109
4.2.10. Dimethyl Acetamide 110
4.2.11. N-Methyl Pyrrolidone 110
4.2.12. Hydriodic Acid 111
4.2.13 Silver Nitrate Solution 111
4.2.14. Bromine Solution 111
11
Page
4.2.15. Potassium Iodide 112
4.2.16 Sulphuric Acid 112
4.2.17. Sodium Thiosulphate 112
4.2.18. Ammonium Thiocyanate 112
4.2.19. Starch Indicator 112
4.2.20. Ferric Ammonium Sulphate 112
4.2.21. Polyacrylamide 112
4.2.22. Nomex 113
4.3.1. t-Butyl Hypochlorite 113
4.3.2. Aqueous Solution of Hypochlorous Acid 114
4.3.3. The o( Form of Nomex 114
4.3.4. Preparation of N-Chloro Nylon 66 115
(a) With tert-BuoC1 115
(b) With HOC1 Solution 116
4.3.5. N-Chloro Nomex 116
4.3.6. Reaction of Living Poly(ethylene- , oxide) and N-Methyl Pyrrolidone
116
4.3.7. Metalation 118
4.3.8. Preparation of Graft Copolymers of Nylon 66 and PEO 120
12
Page
4.3.9. Determination of Ethylene-Oxide Volumetrically 121
4.3.10. Viscosity 123
4.3.11.
4.3.12.
4.3.13.
4.3.14.
4.3.15.
4.3.16.
Determination of Molecular Weight of Nylon 66 and Regenerated Nylon 66. 123
Preparation of Nylon 66 Polyacrylonitrile Graft Copolymers 124
Fractionation of Nylon 66 Acrylonitrile Graft Copolymers 125
Anionic Polymerization of Acrylonitrile 126
Unsuccessful Attempt to Prepare Graft Copolymer of Nylon 66 Styrene 127
Preparation of Sodium Naphthalene 1 27
4.3.17. Metalation of Nomex with Na/NH3 128
4.3.18. Metalation of Nomex with Sodium Naphthalene 128
4.3.19. Unsuccessful Attempt to Prepare Graft Copolymer of Nomex Poly (ethylene-oxide)
129
4.3.20. Preparation of Nomex Polyacrylonitrile Graft Copolymers 130
4.3.21. Proof of the Absence of the Homopolymer Polyacrylonitrile in the Preparation of Nomex Polyacrylonitrile Graft Copolymers 131
13
4.3.22. Preparation of N-Derivative of
Page
Nomex (N-Benzyl Nomex) 131
4.3.23. An Unsuccessful Attempt at the Metalation of Polyacrylamide 132
CHAPTER 5 RESULT AND DISCUSSION 138
5.1. Nomex, N-Chloro Nylons and N- Methyl Pyrrolidon as Solvent ' 138
5.1.1. On Nomex 138
5.1.2. N-Chloro Nylon 66 and N-Chloro Nomex 140
5.1.3. N-Methyl Pyrrolidon as Solvent in Ionic Reactions 143
5.2. Graft Copolymers of Nylon 145
5.2.1. Introduction 145
5.2.2. Metalation Nylon 66 146
5.2.3. Degradation of Nylon 66 in the Metalation Reaction 148
5.2.4. The Grafting of Nylon 66 with Poly(ethylene-oxide) 149
5.2.4.1. Extraction of Homopolymer and IR Spectra 149
5.2.4.2. Determination of the Ethylene Oxide Quantitatively by the Morgan Titration Method 152
14
5.2.4.3. Relation of Metalation and
Page
Grafting 154
5.2.4.4. Solubility 157
5.2.4.5. Phase Separation of Homopolymers 160
(A) Phase Separation 160 (B) Glass Transition of Copolymers 161
5.2.4.6. Crystallinity 166
5.2.4.7. Solution Properties of the Graft Copolymers 173
5.2.5. The Graft Copolymer of Nylon 66 Polyacrylonitrile 182
5.2.5.1. Solubility 182
5.2.5.2. IR Spectra 184
5.2.5.3. Thermal Degradation of Nylon 66-g-PAN 184
5.2.5.4. Thermal Analysis 187
5.2.6. Metalated Nomex 187
5.2.6.1. Nomex-g-Polyacrylonitrile 189
5.2.6.2. N-Benzyl Nomex 192
5.2.6.3. Unsuccessful Attempt to Prepare Nomex-g-PEO, Nylon 66-g-Polystyrene; The Metalation of Polyacrylamide 193
15
2aa2.
5.3. Influence of Heterogeneous Media on Products 195
5.3.1. Introduction 195
5.3.2. Influence of Heterogeneous Media" on Nylon Systems
196
CHAPTER 6 CONCLUSIONS 201
_.REFERENCES 263
16
CHAPTER 1
SYNTHESIS OF BLOCK COPOLYMERS, GRAFT COPOLYMERS AND BRANCHED HOMOPOLYMERS
1.1. Introduction
It has been known for a long time that the
simultaneous polymerization of two or more olefinic
monomers yields random copolymers, the properties of
which are different from those of a mixture of the
corresponding homopolymers. The physical properties
of these random copolymers depend in part on the
chemical nature, the molar composition and the internal
structural arrangement of the constituent monomer
repeat units. The thermal history of the copolymers
may also affect their physical properties.
The theories which account satisfactorily for
the behaviour of linear homopolymers sometimes fail
to predict the behaviour of several other types of
macromolecules, such as block or graft copolymers
and branched homopolymers. 1
The different properties
of some of the latter types of polymer has stimulated
the recent development of methods of their synthesis.
A block copolymer may be defined as a polymer
composed of molecules in which two or more polymeric
segments of different chemical composition are attached
end to end. A graft copolymer is distinguished from
17
a block copolymer in being a branched copolymer in
which one or more polymeric segments are attached
pendantto the chain backbone of a different polymer
species. An example of a block copolymer of monomer
M1 and M
2 is:
(M1-M1-M1
M14-(M
2 M2
N2)
and a graft copolymer is:
M -M -M -M -M -M -M 11 1 1 1 1 1
I
12 I2
M M2
1 2 12 M2
M2
In a block copolymer three different intereaction
parameters have to be considered : between two M1
segments, between two M2 segments, between an M1 and M
2 segment. The latter type of interaction is
frequently reduced in block copolymers wheh intra-
molecular phase separation occurs.2
However, in
graft copolymers heterocontact intereactions are
more important and the branched structure of the
molecule also has to be considered.3
Block and
graft copolymers are sometimes termed sequential
polymers since they incorporate sequences of
monomer units of the same type. The only fundamental
difference between the method of synthesis of block
and graft copolymers involves the location of active
sites or reactive groups. A block copolymer is produced
when the active sites involved in the synthetis
were previously at the ends of the chains. However,
if the active sites are situated along the polymer
chain, graft copolymers will be prepared.
1.2. Summary of Methods of Synthesis of Sequential Polymers
The field of synthesis of block and graft
copolymers is conveniently classified according to
the mechanism of synthetic procedure. Thus block
and graft copolymers may be synthesised by:
1.2.1. Free Radical Mechanisms
(a) Chemical Methods
(b) Photolytic Methods
(c) High Energy Irradiation Techniques
(d) Mechanochemical Methods
1.2.2. Ionic Mechanisms
(a) Anionic Mechanisms
(b) Cationic Mechanisms
1.2.3. Co-ordination (Ziegler-Natta)Polymerizations.
1.2.4. Miscellaneous Ring Opening
1.3. Free Radical Mechanisms
Many attempts to synthesize block or graft
copolymers proceed in two steps. The first step
.1.8
19
involves preparation of homopolymer sequences containing
active sites. The second step involves polymerization
of the second monomer using the active sites as free
radical initiators. If the sites are located at
chain ends, a block copolymer will be obtained. If
the active sites are distributed randomly along the
chain, the process will yield graft copolymers. In
both cases, homopolymers will be present in the reaction
medium and have to be separated by careful fractionation.
Numerous methods of this type have been
developed but they have the disadvantage that they do
not readily yield sequential polymers of narrow
molecular weight distribution (model macromolecules).
The classification mentioned is based on the
method of generation of free radicals. These methods
can be further subdivided along general characteristics.
1.3.1. Synthesis Free Radicals : Chemical Methods
(a) Chain Transfer to Polymers
This method can be illustrated by the following
scheme:
M. R. +...........CH -CH.,.
2 , 1 (M) (initiator radical) X
11 • +nM , n-1 -)-CH -C- , -CH -C- 2 4 1
.5, )( X (1-1)
/ +-CH-
(polymer 2 ,
radical X
20
Benzoyl peroxide (BPO) was used as initiator for the
grafting of methyl methacrylate onto polystyrene.
A large amount of graft product was obtained whereas
with azobisisobutyronitrile (AIBN) much less grafting
occurred.4
Methyl methacrylate can also graft easily onto 5
natural rubber using BPO, but little grafting results
with AIBN. Thus grafting efficiency and graft yield
are strongly affected by the free radical source.
The inactivity of AIBN might be due to resonance of
cyanopropyl radical (CH3)2
CCN whereas the benzoyloxy
radicals C6H5COO., are less stabilized. These kinds
of copolymers can be prepared generally by dissolving
a polymer to be grafted in the monomer or in a
monomer-solvent system and then introducing an
effective free radical source. The grafting reactions
are governed by the reactivity of both the radical and
monomer.6'7 Graft copolymers can also be prepared by
introducing epoxy groups into a chain,8 for example:
H3
CH3 Thioglycolic Acid
C • 1 ,
.w.' CH -Civw AN4ACH-Cv■A'w 2 a COOCH
2-CH-/H2
COO-CH2 -CH
t , 2 0 9 0
co co 1 1 CH CH
2 SH SH
(1-2)
The side group can be used to prepare graft copolymers
utilizing the high transfer reactivity of the thiol
(-SH) groups.
21
Another method for the preparation of graft copolymer
by free radical chain transfer is to use halogen atoms
on a polymer backbone as initiation site. For example 9
Schonfield synthesized a polyester
CH Br 2
[-O-CH2 -C-CH
2 -0-00-(CH
2)4-CO-)
CH2Br
and used it to graft polystyrene by transfer.
There are two main disadvantages involved
in this technique. Firstly, in addition to the
desired graft or block copolymers, there is always
some homopolymer formed due to chain transfer to
monomer, direct initiation, or because not every
performed macromolecule enters chain transfer.
Secondly, the degredation may occur in the main
chain during the course of the grafting reaction.
Any of the above effects could necessitate laborious
purification of the products in order to obtain
homogeneous sequential products.
(B). Reaction of Reactive Groups in the Chain
Suitable reactive groups involving unsat-
uration, peroxide or perested linkages, diazonium
salts, etc can be introduced into the performed polymer
C\
22
either by copolymerization of small but controlled
amounts of a suitable monomer or by post-polymerization
treatment, such as oxidation or peroxidation. These
reactive groups can then be transformed into radicals
capable of initiating the polymerization of a monomer.
(i) Unsaturation in the Chain
Allen et al5 used C14 labelled benzoyl peroxide
at 60°C in benzen to initiate the grafting of MMA to
natural rubber. When AIBN was used instead of BPO only
homopoly (methyl methacrylate) was formed and no graft
copolymer. Thus there is no chain transfer of growing
PMMA radicals with polyisoprene.
Impact resistant polystyrene is produced
commercially by dissolving a suitable elastomer, such
as natural rubber (synthetic cis - 1,4 polyisoprene) in
styrene monomer and initiating the polymerization -
grafting of the latter by introducing an initiator such
as BPO.
(ii) Peroxide Groups
Peroxide, hydroperoxide, perester and similar
groups are particularly active for initiating chain
grafting or block copolymerization. By analogy with
the well known oxidation of isopropylbenzene, the
oxidation of polystyrene by air or oxygen would be
expected to give hydroperoxides in the o<_ position.
However, polystyrene is difficult to peroxidize directly
so styrene is often copolymerized with a small amount of
P-isopropyl styrene, which is sunsequently peroxidized
with oxygen.10-13
-CH2 -CH-
me-c-me H
02 ++
Fe
-CH2-CH-
-(C■
Me-6-Me7
O.
23
(1-3)
Me-c-Me 0
H
I +M
homopolymer + graft copolymer
Methyl methacrylate or vinyl acetate have been
grafted to polystyrene by direct thermal decomposition
of the peroxide1 o4 r by a redox mechanism with Fe2+ salt.
13
Ozonization can also be used to introduce
peroxy groups into a polymer. The ozonization method
has been extended to many widely different polymer
monomer systems, such as polybutadiene/acrylamide
cellulose/styrene, cellulose/acrylonitrile15 and
starch/styrene.16
Smet et al17 prepared a block copolymer
of methyl acrylate and t-butyl peracrylate. The
copolymer which contained about 2% of the per-
compound was heated in the presence of styrene
monomer and poly (methyl acrylate-g-styrene) was
prepared.
Polymeric acid chlorides can be converted
to peroxy (or perester) groups which are able to
initiate the polymerization of vinyl acetate
19 and/or methyl methacrylate:
-CH2 -CH-
4
NH2
24
PC15
(CH3)3COOH
-CH -CH-CH 2 , -CH- 1' -CH -CH-CH -CH-
2 , 2 , COOMe COOMe COOMe CO
Cl
-CH2-CH-CH2 -CH-
, COOMe CO
(1-4)
0-U-C(CH3)3
Smets et al initiated the polymerization of
styrene by a peroxide such that the product had
peroxide groups in terminal or chain positions:
•O-CO-C6H5CO-0-0-CO-C
6H5CO-0-
When a solution of this polymer was heated
in the presence of methyl methacrylate the monomer
polymerized.20,21
In order to prepare peroxy groups
other methods have also been used.22,23,24
(iii) Diazo Groups
Graft copolymers can be made using the
polymeric radicals derived from diazonium salts by
one of the following schemes:25
4++ + N
2 + Fe + Cl
(1-5)
25
or by26
-CH2 CH- ,
CH2-CH- -CH -CH-
2) o 112S / .14
NH
COCH3
(1-6) N -NO
COCH3
(iv) Macromolecular Redox Initiators
Mino and Kaizerman27 synthesized various graft
copolymers with a polyvinyl alcohol backbone and
polyacrylamide, polyacrylonitrile and poly (methyl
methacrylate) branches using ceric salts. The base
is some organic reducing agent such as an alcohol
or an aldehyd which can be converted to radicals by
one electron transfer to ceric (iv) ions. For
example:
+4 Ce+R-CH2OHT=t[ceric/alcohol complex] ____4.
3+ Ce+H+ RCHOH(RCH
20e) (1-7)
In ceric systems, since the radical is formed only
on the backbone, the homopolymerization is minimized
and a clean graft copolymer can be prepared. Graft
copolymerization of cellulose with redox systems has
been summarized.28
26
1.3.2. Photolytic Methods
Selective absorption by well defined chemical'
groups of electromagnetic radiation in the visible
and U.V. region may result in bond cleavage and
consequently in radical formation which, in turn,
may lead to polymerization initiation. Block and
graft copolymers can be synthesized by this general
method. If none of the bonds in a polymer can absorb
C) radiation, then some photosensitizer must be added.
Photosensitizers can absorb light and are able to
transfer light energy to other species in the
system. In the following, both methods of direct
and indirect (photosensitizer) initiaton will be
mentioned.
(a) Direct Methods
Some polymers can be decomposed directly,
e.g. by photolysis or by irradiation, giving macro-
radicals which act as new centres for monomer
addition.
By ultraviolet irradiation of a solution
of polymethylvinylketone in dioxane, carbon monoxide
and acetaldehyde were evolved. Simultaneously, the
molecular weight decreased and some unsaturation
appeared.29,30,31 The following reactions give
an interpretation of these phenomena:
27
-CH2 -CH-CH2-CH-CH2 -CH- -CH2 -CH-CH2C • -H-CH2 -CH- , I , hv , , , CO CO CO ----- CO CO 1 1 1 1 1 CH3 CH3 CH3
(I) CH3 CH3
+ CH3CO- (or CH3 + CO)
-CH -CH-CH2-CH-CH -CH- 2 2 CO CO CO -V *CH3 . 1 • I CH3 CH3
• • - CH2 -CH- + CH2 -CH-CH2 -CH Tffil. , , ---). ,
CO CO CO I I I CH3 CH3 CH3
(1-8)
(1-9)
(1-10)
-CH -CH CH =C-CH -CH- -CH=CH CH -CH-CH 2 2 , , CO2 2 2
+ CO CO Or CO 3
+ CO CO 1 / v I' 1 1 CH3 CH3 CH3 CH3 CH3 CH3
The same photolysis carried out in the presence of
acrylonitrile yields graft copolymer29 (I and II) and possibly some block copolymers (III) together
with some homopolymer. The predominant formation
of graft copolymer must be due to radicals produced
in reaction schemes I and II.
Styrene can be polymerized (thermal or by
U.V.) in the presence of CC13Br
28
CC13Br heat CC13 + Br + nS -------pu
U.V.
C13C-S-S-S-- • -S-S-Br or
Br-S-S-S - - - - - - S-S-Br or (1-12) CI 3C-S-S - - - - - - - - S-S-CC13
The polystyrene which has been prepared by this method
contains some halogen. On irradiation, carbon-
halogen bonds can be broken and in the presence of
methyl-methacrylate a mixture of homopolymer and poly
(styrene-b-methylmethacrylate) can be prepared32
Jones3,3 prepared a polystyrene containing
about 3% bromine, with the bromine atoms attached
to the backbone which was used for grafting with
methyl methacrylate by U.V. photolysis.
(b) Indirect Methods
Photosensitizers upon irradiation may give
rise to radicals which in turn.may interact with a
polymer in the system by removing an atom or group
of the chain and thus ultimately provide radicals
on polymer chain. Oster et al described the grafting
of acrylamide to rubber containing benzophenone
and the surface grafting and crosslinking if solid
high polymers, such as polyethylene with styrene
and methyl methacrylate.34,35,36,37 Photosensitive
29
dyes (e.g. anthraquinone - 2,7 disulphonic acid
sodium salt) were used to prepare graft copolymers
of cellulose and cellulose derivatives by Stannet
et al.36 The authors believe the photoexcited dye
molecule can abstract a hydrogen atom from the
cellulose and form a free radical.
0
0'
0 OS ; .
SO3 hv --;•
cellulose
•0
+M + cell graft (1-13)
H
1.3.3. High Energy Irradiation Methods
During the last decade high energy irradiation
has been extensively developed for polymerization
initiation and the preparation of polymer derivatives.
High energy irradiation methods can be generally
divided into:
(a) Direct or mutual irradiation
(b) Preirradiation
There can be some subdivided methods depending on the
medium of irradiation e.g. in the presence of oxygen,
in vacuo, in emulsion or solution.
30
(a) The Direct or Mutual Irradiation Technique
In this technique, the polymer is dissolved
or swollen by the vinyl monomer and sometimes the
vinyl monomer can be in the vapour phase. Graft
copolymerization starts at the radical sites
generated along the polymer backbone.
In direct irradiation, diffusion of the
monomer into a polymer affects copolymer formation.
Systems become more complicated when the polymer
is crosslinked upon irradiation. Crosslinking and
grafting could occur by increasing the dose rate,
and monomer diffusion to the reactive site may
become rate limiting. The rate of grafting might
increase autocatalytically, for example, by
decreasing the rate of termination in a viscous
media.
The influence of the polymer structure
on the irradiation grafting has been examined in the
case of styrene grafted to high pressure and low
pressure polyethylene film.38 The most important
factors which determine the efficiency of grafting
are the degree of crystallinity, the thickness of
the film and the dose rate. Grafting is favoured in
amorphous regions and on the surface of material where
monomer can easily penetrate. During grafting of
styrene to polyethylene38
it was observed that
grafting continued long after irradiation stopped.
This suggests the survival of occluded active
31
radicals in polymer matrices. This post-effect can
be used for increasing the efficiency of grafting
by the intermittent technique whereby the monomer
is allowed to diffuse into the polymer which is
subsequently exposed to relatively short bursts of
irradiation, preferentially at low temperature.39,40
Direct irradiation techniques have been
used for the preparation of various rubber/vinyl
monomer grafts. Polyisoprene can be crosslinked
upon irradiation. In the presence of methyl
methacrylate,41
grafting commences on the rubber
backbone. The first step for grafting is probably
the formation of polyisopropenyl plus hydrogen
radicals. For some reason the hydrogen radical H.
does not lead to the formation of much free poly-
methyl methacrylate (PMMA) and evidently radicals
from the monomer react faster with cis 1,4 polyisoprene
than with its own monomer. Graft copolymers of
rubber and MMA can be prepared by a redox system, but
under similar conditions (rubber latex swollen with
MMA) graft copolymers prepared by ' rays contain much less homopolymer. Also the molecular weight of the
PMMA branches is higher and the film forming properties
of the grafted material are also superior. In the
redox system grafting is concentrated on the surface
of the latex particles due to non-uniform diffusion.
32
Non selective irradiation of two polymers
can cause bond breaking which might result in cross-
linking grafting and/or block formation, etc.
shAvvvvvyvvyv
wvvve•AA
T
(1-14)
This is a very inefficient technique for the preparation
of sequential copolymers and has not been studied
extensively.
(b) Preirradiation Techniques
The preirradiation method is used especially
with crystalline polymers. Irradiation of such
polymers yield trapped radicals and these sites act
as initiators on contact with another monomer. The
grafting process lasts only for a short time, until
all radicals have disappeared. The polymer is
preirradiated in air (oxygen) or in the absence of
air (oxygen). The preirradiated method is sometimes
called the "trapped radicals method". To maximise
the generation of immobile trapped radicals, pre-
irradiation is better performed below the Tg of
the particular polymer. After preirradiation and
introduction of the monomer, the system can be
heated to accelerate branch formation. In this
system, the amount of homopolymer can be minimized
since the monomer has not been irradiated directly.
33
If a polymer is preirradiated in air, peroxy
radicals, R0"2 are formed initially and subsequently
peroxy and hydroperoxy groups may result. These
peroxides can be used in subsequent reactions to
initiate grafting of vinyl monomers. Any hydro
peroxy groups ultimately lead to homopolymer
formation.
(1-15)
1
- C-C-C-
other possibilities
1 02
1 1 1
- C-C-C-
1 1 t
O
O
V N. 1 1 1 1 1 1
1 1
0 1 1 1 1
0
o 0 1 1 1
-c-c-c- I I I
00H %It
Homopolymer
1 1 1
2-C-C-C-
9
Graft copolymer
34
Bevington et a142
prepared some graft copolymers by
preirradiation techniques. Sakurada et a143 grafted
styrene to cellulose by preirradiation in dry air
and also in vacuum. Irrespective of the mode
of preirradiation, the percentages of polystyrene
grafted were the same. E.S.R. spectra of cellulose
irradiated in vacuum or in air were identical, so
initiation is thought to be by trapped R., rather
than R02.•
1.3.4. Mechanochemical Methods
The formation of free radicals for initiating
the polymerization of a second monomer can also be
obtained by the scission of the polymer molecule.
In general, sequential copolymers can be
prepared by:
(a) Subjecting a mixture of two or more
polymers to mechanical degradation
(b) Subjecting a polymer to degradation
in the presence of a polymerizable monomer. The
degradation of high polymers by free radical paths
may be accomplished by a number of ways:
(i) Cold mastication, milling, extrusion
above Tg.
(ii) Dispersing or vibro-milling below Tg
of amorphous and crystalline polymers.
35
(iii) Ultrasonic irradiation of polymer
solutions.
(iv) High-speed stirring or shaking or
the forcing of polymer solutions through
narrow orifices.
(v) The freezing and thawing of polymer
solutions.
(vi) The discharging of high voltage
sparks through polymer solutions.
(vii) The swelling of crosslinked or
high entangled polymers by monomers from
the vapour phase.
The above methods of producing sequential
copolymers have been reviewed.44
All these methods
involving radical processes have been used to produce
graft copolymers, but a full characterization of all
the reaction products does not appear to have been
achieved.
1.4. Synthesis by Ionic Mechanisms
A large amount of research has been carried
out in the field of ionic block and graft copolymeriz-
ation. Indeed, ionic synthesis provides excellent
methods for the preparation of sequential copolymers.
36
1.4.1. Synthesis by Anionic Methods
Anionic polymerization is an outstanding
method for the controlled synthesis of many polymers.
The synthesis can be controlled by altering a number
of variables such as the type of initiator, the
monomer structure, the environment of the growing
polymer chain and the presence or, more important,
the absence of termination.
A monomer must satisfy certain criteria
before it can be made to polymerise via an anionic
mechanism
(i) the monomer must be capable of forming
a stable anion;
(ii) the anion derived from the monomer must
be capable of propagation;
(iii) the monomer must contain no reactive
groups which could be attacked by the anion other
than the conventional attack on the double bond; and
(iv) the anion must not isomerise to a
stable form.
Examples of classes of monomers, which are shown in 45
order of decreasing reactivity, are styrene> dienes)
acrylic esters) cyclic oxides) isocyanates >
nitroalkenes. The polymerization is initiated by
the transfer of electrons from a suitable initiator
to the monomer, thereby forming an anion. The
important feature of anionic polymerization is the
absence of termination reactions under suitable
conditions. The termination reaction is usually
37
brought about deliberately by the introduction of
a specific reagent. The synthesis of sequential
polymers by anionic mechanisms has been reviewed
and summarized recently by several authors.46-55
1.4.2. The Application of Anionic Processes to Block Copolymer Synthesis
(a) General Considerations
The important characteristics of the
anionic polymerization processes described in the
previous section are the absence of a termination
step, control of molecular weight and molecular
weight distribution and the capability of polymeric
anions to initiate the polymerization of some other
monomers. These features suggest that anionic poly-
merization is a technique by which well characterized
block copolymers, free from contaminating homopolymers,
may be synthesised.
(b) Coupling Reactions
ABA block copolymers may be prepared by a
sequential polymerization of monomer A followed by
monomer B and finally monomer A. The synthesis of
the three component block copolymers may be achieved
by an alternative route in which AB copolymers are
joined by a coupling reaction between living polymeric
anions and a difunctional reagent.
- - AB Li+ + X(CH2)nX + Li BA ---vAB-(CH
2)n-BA + 2LiX
(1-16)
38
If n is small, the product will be essentially
an ABA copolymer. In addition to modifying the sequential
process, this approach provides a route to ABA block .
copolymers in cases where B is too weakly basic to
initiate monomer A to form a third segment (for
example when B is methyl methacrylate and A is
styrene). A number of coupling agents have been
described in the literature, the main details occurring
in patents. It has been claimed that dibromo compounds
in which the two halogen atoms are situated on the same
or adjacent carbon atoms were most active in coupling
reactions.56
Alternative coupling systems which have
been applied to living anions including divinyl armatic
compounds,57
carbon dioxide, c arbon disulphide and
carbonyl sulphide,58,59
the ha logens,60 bis-haloalky-
lethers,61
carbon monoxide and metal carbonyls.62
The
mechanism of coupling for these agents is not so clear
cut as with the dihaloalkanes and their efficiency in
some cases is rather dubious. Carbon dioxide can be
used as follows:-
RL+CO2
RCO2Li RLi
a
R 0-Li
C /7
R 0-Li
Ha
(1-17)
R-C-R+Li0H+LiX
0
Although in some cases the product is mainly a.
R -I + Lii
RI + RLi R-R + LiI
RLi + I2
(1-22) COOEt
CO-C AA-AA"
COOEt CO-C.41/4" +- NaCANv
Na- Ciwe
+ 2Na0Et
39
With iodine as a coupling agent:
Tsutsumi et a162 suggest that carbon monoxide
couples by the following mechanism:
0 2RLi + 3C0 R-C-R + 2LiC0 (1-20)
The coupling reaction with COC12may be shown
as:
Afte'vENI + COC12 -I- NIE-ww
+ 2NaC1
0
(1-21)
With diethyl terephthalate the reaction is:
The different coupling agents have different efficiencies.
Improvement in coupling results if the counter ion is
potassium,63 which eliminates side reactions such as
metal halogen interchange which can occur in lithium
systems
AwyCLi+ + C1CH2Cl 'CC1 + LiCH2C1
(1-23)
40
The presence of tetrahydrofuran64 and similar polar
solvents increase the rate of coupling and thus the
efficiency of coupling also increases. The polymeric
living anion is susceptible to termination by a wide 65
variety of compounds such as:
TABLE 1-1
Synthesis of Reactive End-Group Polymers
,Terminating Agent
Resultant End Group
Polymer Terminated
Reference
CS2
-CSSH S,B 66,67
O\
-CH2-CH2OH
B,I 66,68 CH2 CH2
SOC12 -SOC1. S 69
Br(CH2)6Br -(CH2
)6Br S 69
NCO
NCO I 49
Key S = Styrene B = Butadiene I = Isoprene
41
The use of terminally reactive polymers to prepare
block copolymers has so far received little attention.
Hayashi and Marvel68
have prepared polystyrene
dicarboxylic acid by terminating polystyrene dianions
with carbon dioxide and polybutadiene diglycols by
reacting the appropriate dianions with ethylene oxide.
Solution polycondensation were effected by heating the
diacid and diglycol in refluxing toluene, but only low
degrees-of-polycondensation could_be achieved. The use
of acid ended polymers to form polyesters by reaction 0,71
with alcohols has been reported in patents7, but few
detailed examples have appeared in the journal
literature. Aoki72
polymerized styrene with sodium in
liquid ammonia to give a polymer containing terminal
amino groups which were then reaction with epichlorohydrin
.,AAmisNH2+C1CH
2 -CH-CH
2 ----4 wW7 -CH -CH-CH (1-24)
/ 2 \ 2 '0. Of
This reaction product was then treated with 8F3,0Et2
and the adduct used to initiate the polymerization of
T.H.F. to give a poly (styrene-b-tetrahydrofuran)
copolymer.
When living polystyrene is reacted with a small
amount of P-divinylbenzene and quickly deactivated
with a proton donor, the molecular weight is unchanged
but some double bonds remain pendant at the end of
polystyrene chain. The species obtained can then be
copolymerized through these double bonds by any
method applicable to styrene, free radical, cationic
or anionic polymerization. The best result so far
has been obtained anionically.73 Several attempts
42
were made to prepare graft copolymers using cationic
initiator and adequate monomers. Since transfer
reactions often occur in cationic polymerization
processes, however, most of these attempts were
unsuccessful, since chain ends do not retain active
sites.74 Berger and Levy
75 studied the reaction
between the polystyrene anion and living cationic
tetrahydrofuran and concluded that block copolymers
were formed. But Vandenberg76
has shown that anions
will cleave polyethers by reaction at the -C-0- linkages, and that in polytetrahydrofuran this is
the predominant reaction, so that efficient linear
block copolymer formation through mutual termination
of anionic and cationic species is unlikely.
1.5. Graft Copolymers
Basically, there are two procedures by which
anionic graft copolymers can be produced. In the first
procedure, a polymer having a reactive end group, is
prepared and then allowed to react with a polymer
backbone having suitable functional groups. In the
second procedure, anions are generated on a performed
polymer backbone and the anionic sites are then used
to initiate the graft polymerization of monomers
subsequently added.
43
1.5.1. Grafting of End Functional Polymers onto Polymer Backbones
It is well known that carbanionic sites do
react with various electrophilic functions such as
- acid chlorides, esters, nitriles and anhydrides.7779
The procedure consists of preparing a polymer having
a carbanion end-group and then using the carbanion to
graft the branch onto a polymer backbone having groups
reactive toward such carbanions.
Thus living polystyrene has been prepared
in T.H.F. using Phenylisopropyl potassium as initiator
and the solution then added to a solution of poly
(methyl methacrylate) or poly (vinyl chloride).80-82
The procedure is, however, far from ideal, since only
a small percentage of the ester groups are able to
react. This is very likely due to a collapse of the
partially graft polymers to form an inner shell of
poly (methyl methacrylate) and an outer shell of
polystyrene and to the fact that only those ester
groups that are on the surface of the collapsed
structure are available for grafting.83
However,
it has been claimed84
that the grafting of living
polystyrene to poly (methyl methacrylate) is not
a random process, but occurs preferentially on
molecules of poly (methyl methacrylate) that have
already reacted. The non-random grafting was assumed
to arise by an uncoiling of the poly (methyl
methacrylate) molecules as a result of the grafting
process, so that the ester groups of partially
44
grafted molecules are more accessible to further
grafting. When living polystyrene is added to poly 85
(vinyl chloride) a competing elimination reaction
takes place. Polystyrene can be grafted onto
rubbery backbones, but these must contain double
bonds.86
Reactive sites are created on the rubbery
backbone by adding bromine to the double bond, and
the grafting reaction takes place by reaction of
the living polystyrene with brominated sites.
Again side reactions might occur.
R R I + - 1
CH3 1 -C-Br+LiPs -----* CH
3-C-Li+-Ps-Br (1-25)
R!' 11`
R R R R 1 I 1 1
CH3 1 -C-Li + CH
3 -C-Br- CH
3 -C-C-CH
3 +LiBr
1 —>
i 1 RI le Re It'
(1-26)
This method of anionic grafting is restricted to
a small number of cases. But it is one of the preferred
methods to synthesize graft copolymers for morphological
investigations, since characterization of the structure
of the molecule is easy.. The length of the backbone,
the number and the average length of the grafts are
experimentally accessible. Furthermore, the random
distribution of the graft is expected if a suitable
homogeneous system is chosen.
45
Grafting of cationic polystyrene onto poly
(2,6 dimethoxystyrene) has been reported.87
Yields
are moderate but characterization of the graft
copolymers is not very easy.
1.5.2. Generation of Anions on Polymer Backbones
Polystyrene has been metalated with potassium
metal and sodium oxide88
but only in yields between
0.2 and 1%. A more satisfactory procedure for
metalation of polystyrene involved iodination with
iodine and iodic acid in nitrobenzene followed by
reaction with butyllithium.89
Iodination takes
place in the ring and the metalation can be nearly
quantitative. Metalated polystyrene has also been
prepared by the reaction of butyllithium with
poly-0, m or P bromostyrene.90
P-Chlorostyrene,
or its copolymers with styrene, have been metalated
with sodium naphtalene in T.H.F. and the resulting
macromolecular polyanions used to initiate the
polymerization of acrylonitrile, vinyl pyridine,
methyl methacrylate or styrene.91,92
&vv./CH2 -CH .4.44%,
+ 2Na
Cl
Nvol-CH2 -CH
(1-27)
+ NaC1 + 2
46
Kennedy93
developed a synthesis which gives
rise to essentially pure graft copolymers. This
method is based on the discovery that certain
alkyl- aluminium compounds e.g. Et2A1 Cl, Et3A1
initiate the polymerization of cationically active
monomers only in conjunction with purposely added
alkyl halide e.g. t-BuX. According to this
technique, suitable polymeric halide can initiate
the polymerization of various monomers e.g. iso-
butylene, styrene, dienes, etc. In a typical
synthesis, lightly (approximately 3%) chlorinated
poly (ethylene-co-propylene) is stirred with styrene
monomer and Et2Al Cl is added. Grafting starts
immediately and in approximately 30 minutes the
reaction is complete. Besides this graft of poly
[(ethylene-co-propylene) -g-styrene], a series of
other grafts have also been prepared, e.g. poly
[(isobutylene-co-isoprene) -g-styrene] etc.
Attempts to metalate poly (vinyl chloride)
with butyllithium in THE only leads to complex
reaction where butylation, dehydrochlorination and
partial metalation appear to have taken place.94
Direct metalation of polymers that have acidic
hydrogen is a facile reaction and well defined
materials have been produced. An interesting case
is provided by poly (diphenyl-3,3 propen-1). This
material cannot be prepared by the polymerization
of the corresponding olefin because of a rearrange-
ment reaction
(1-28)
H-CH=CH2 ----+ C=CH-CH3
47
but can be prepared high pure by:
Sodium Naphtalene
-CH -CH-CH2 2 t
1 -78 C T.H.F. CH / 0
H
(PLCHNa
-CH2 -C-CH
2 - --------
C1
(1-29)
-CH-CH -CH- 2 2
Na.
Poly (diphenyl-3,3 propen-1) can be easily and
quantitatively metalated with sodium naphtalene
in T.H.F.95-97
Tripolymers have been prepared by
using partially metalated polymers and allowing
the sites to initiate polymerization of one
monomer. On remetalating the remaining sites,
after isolation of the intermediate polymer, a
second monomer can be added. In this way
poly (dipheny1-3,3-propen-1) having polystyrene
and poly (methyl-methacrylate) branches has
been prepared.97 Though polystyrene itself is
rather hard to metalate, this was achieved by
48
. • using n-butyl lithium complex with N,N,N,N-tetra-
methylethylene diamine.98
Metalation of poly
[2-vinylfuran](I) and poly [2-vinyl-fluorene](II)
by lithium naphthalene has been reported.99,100
-CH2 -CH- , -CH-CH- 2
Generally, in this method a polymer chain contains
organometallic sites distributed randomly and these
• sites are used to initiate the polymerization of an
appropriate monomer.
1.6. Co-ordinative Methods
Stereospecific catalysts can give stereo
block copolymers. Greber101
used a Ziegler-Natta
co-ordination catalyst for the synthesis of grafts
onto poly(styrene-co-butadiene) and other polymers
containing pendant vinyl groups. This author first
reacted diethylaluminum hydride with a suitable
backbone and obtained a macromolecular trialkyl-
aluminium:
Et2AlH +
CH CH 2
CH2 CH2
Al N
Et Et
(1-30)
49
This trialkylaluminum was then employed in the
preparation of a Ziegler-Natta catalyst with TiC14
or TiC13 etc and used in the polymerization of
ethylene, propylene or other o(-olefins. By
using molecules with two terminal vinyl groups,
this basic technique can also be used for the
synthesis of block copolymers. For example,
Greber described the following process:
CH3
CH -Si-CH2
-CH=CH2 3 1 CH CHCH3
+2Et2AIN CH3 Si-CH3 > CH3-Si-(CH2)3AlEt2
CH2 CH
3 -Si-CH
2-CH=CH2
CH3
(1-31)
+TiC14 CH3 -Si-CH2-CH2-(C2H4 n )-
nC2H4
1.7. Ring Opening
Polymers containing a variety of acidic or
basic groups, e.g. -OH, -COOH, -NH2, -SH, atc. can
be used as potential backbones for the synthesis
of sequential copolymers. Block copolymers will be
CH I 3
50
obtained if the functional groups are at the ends,
whereas grafts will be produced if they are
randomly distributed along the chain. Block
copolymers were prepared by initiating the poly-
merization of propylene oxide by a base so that
both the head-group and the end-grcup become
hydroxy units. This double-headed hydrophobic
sequence is then used to initiate the polymerization
of ethylene oxide to obtain a hydrophobic sequence.
The product is a triblock polymer, poly (ethylene
oxide-b-propylene oxide-b-ethylene oxide).
HO-{Et0}--(P0)---(Et03--H
These materials are nonionic detergents and are
commercially available.
Poly(ethylene oxide) branches can be readily
attached to nylons since the hydrogen atom of the
amides nitrogen are easily removed.
-ovvvv C 0: 11 AA.4.44,44, + nCH -CH 2 2
0
eK4,CON,~ (CH-CH-
20) nH
(1-32)
1.8. Branched Homopolymers
The study of branched homopolymers has
attracted great interest in recent years for two
reasons. One is that the commercial linear polymers
often contain branched components which greatly
affect the properties of the polymers. The branched
component in high pressure polyethylene polymerization
is a well known example. In some cases branching may
be intentionally introduced into linear polymers to
51
improve their properties. The other reason is that
branched homopolymers are important in the study of
both the solution and viscoelastic properties of
polymers.
Branches in industrial polymers are usually
classified as long or short. The discussion will be
confined to the effect of long branches whose molecular
weights are as high as those of ordinary linear polymers.
Branching affects the solution properties of the polymers
as well as their mechanical behaviour. But to investigate
systematically and efficiently the influence of branching
on behaviour, model macromolecules must be used. There
are roughly three types of branched polymers:
(1) Randomly branched polymers which are
made by polymerization of monomers
with a statistical probability of
branching.
(2) Star-shaped polymers.
(3) Comb-shaped polymers.
Recently, major interest has been devoted to
branched molecules of rather simple molecular structure.
Two types of branched model macromolecules, comb-like
polymers and star-shaped polymers have been investigated
in great detail in several laboratories. The methods of
preparation of these two model structures will be described
here.
52
1.8.1. Comb-Like Polymers
The preparation of star-shaped and comb-
shaped homopolymers (see Figure (1-1)) is an illustration
of the versatility of living polymers in chemical
synthesis. We shall describe here two methods of
grafting via carbanionic deactivation although
methods using anionic initiation from a metalated
backbone has also been done.
comb-shaped polymer star-shaped polymer
(Figure (1-1))
1.8.1. (a) Coupling Method
In this work,102,103 monodisperse polystyryl104
anions are prepared and coupled with a chloromethylated
polystyrene. The parent polymer is prepared by
polymerization of styrene monomer with n-butvllithium
in T.H.F. The polystyrene was chloromethylated105
with chloromethyl ether using stanic chloride as a
catalyst.
-1.-~CH -CH- + C1CH 70-7CH 2 2 3
+ CH3OH (1-33)
CH2C1
53
Substitution occurs mainly at the para position105
but crosslinking may take place when substitution
exceeds approximately 10%. The chloromethylated
polystyrene was dissolved in benzene, freeze dried
and then dissolved in T.H.F. in vacuo. These functions
were used in a second step as electrophilic groups to
• deactivate living monocarbanionic polystyrene. It
has been claimed106
that exchange relations between
metal and halogen may take place, but later results
have shown that these side reactions can be neglected
if adequate experimental conditions have been chosen.107
The grafting reaction is nearly quantitative and the
comb polymers thus obtained can be considered to be
real model macromolecules. Since the branched
polystyrene thus prepared contained uncoupled branch
molecules the product must be fractionated. It has
been reported that if the lithium salt of styrene
anion is used, various side reactions occur in the
coupling reactions between the chloromethyl group and
the styrene anion resulting in crosslinking between
parent polymers.108,109 However, it has been shown
that such side reactions are negligible if the potassium
salt is used instead of the lithium salt.
1.8.1. (b) Deactivation Method
The second method 111
uses as a backbone
a random copolymer of styrene and methyl methacrylate.
Such copolymers are obtained using radical initiators.
54
The ester functions of the backbone can be used in
a second step as electrophilic deactivators for an
anionically prepared living polystyrene. It was
found that some of the ester functions were unreacted,
and that a small amount of polystyrene, which was
ungrafted, could be removed by fractionation. This
method has two disadvantages. Firstly, since the
backbone was prepared free radically, it was
heteregeneous in molecular weight and composition.
Hence the branched polymer would also have a broad
MWD. Secondly, the carbonyl group is quite sensitive
to photochemical oxidation and the grafts are attached
to the main chain by means of a carbonyl group.
1.8.2. Star-Shaped Polymers
1.8.2. (a) Preparation of Star-Shaped Polymers by Coupling
In this method, various coupling agents can be
used which are poly halogen derivatives, such as:
(1) SiC14
112
113 (2) 1,3,5 - tris - (bromomethyl) - benzene
(3) 1,3,5 - tris - (bromoethyl) - benzene
(4) 1,3,5 - tris - (chloroethyl) - benzene
(5) Tri-chloromethylbenzene 102,114
The solution of the above coupling agents can
be added to a solution of monodispersed polystyrene
anions. The molar concentration of the coupling
agent added is less than that of the polystyrene
55
anion. This can be confirmed by observing that the
colour of the anions remains after the coupling
reaction is completed. Therefore, if the coupling
reaction occurs, ideally there should be no molecule
with two branches. The slight excess of living
polymer has to be separated carefully afterwards
by fractionation. The main disadvantage of this
method is that it may only lead to star molecules
with three, four or, at the most, six branches.
The reaction is not always quantitative.
1.8.2. (b) By Block Copolymerization
Worsfold et al115
synthesized star-
shaped polystyrene by anionic block copolymerization
of styrene and divinylbenzene (DVB), the proportion
of the latter monomer being of the order of a few
molecules per living end. The samples were found
almost free of linear polystyrene and of very low
polydispersity. The number of branches was found
to be a function of the overall concentration of the
amount of DVB and of the molecular weight of the
linear precursor. To study the distribution of
numbers of branches within a sample, careful
fractionation was required. The standard precipitation
fractionation method is of no interest for that
purpose, since differences in solubilities between
molecules differing only by the number of branches
are very small. Elution chromatography, using a
column fitted with cyclic variation of temperatures116
56
was sensitive enough to yield satisfactory fractionation.
Star molecules with six to twenty branches could be
obtained, but for model molecules, it is better to use
very small proportions of DVB to keep the number of
centre as small as possible.
57
2. BASIC CHEMISTRY OF AMIDES
2.1. Introduction
It is often vital in polymer chemistry to
know how chemical reactivity of an organic functional
group on a polymer molecule compares with the reactivity
of the same group on a low molecular weight analogue.
The classical investigation of polyesterification
reactions by Flory117,118
established that the rate of
reaction of carboxyl and hydroxyl groups do not depend
upon the size of the polymer chains to which they are
attached. The rate of hydrolytic degradation of
cellulose has been treated successfully on the assumption
that the reactivity of the glucosidic linkage is
independent of the size of the molecule in which it
occurs.
We can confidently expect a functional group
on a polymer to exhibit essentially the same reactivity
as the same group in a low molecular weight homologue,
if the following conditions are met:
(1) the reaction occurs in a homogeneous,
fluid medium, all reactants, interemediates,
and products being soluble in the medium;
(2) each elementary step of the reaction
involves - no more than one functional
group attached to the polymer, all
other reacting species being small
and mobile; and
58
(3) the choice of a low molecular weight
"homologue" is made with sufficient
care, attention being given to the
steric hindrance that can arise in
the immediate vicinity of a polymer
chain.
The above are suggested as sufficient conditions for
equal reactivity of a polymer and its small homologue.
Essentially equal reactivity may be observed in cases
even where one or another of these conditions is not
met.
Since the reactivity of functional groups
attached to a polymer chain is, in many cases, similar
to the reactivity of such groups in small molecules,
in this chapter it is sufficient to review some
aspects of the chemistry of amides.
2.1.1. Methods of Preparation
Simple amides can often be obtained:
heat (1) R-0O
2 NH4
R-CONH2 + H2O (2-1)
heat (2) R-0O
2 H + H
2NCONH
2 RCONH
2 + CO
2 + NH
3 (2-2)
(3) RCO2 + NH
3 --a. RCONH
2 + R-OH (2-3)
However, the most important general method for
obtaining amides and N-substituted amides is by the
action of ammonia, or a primary or secondary amine,
on an acid halide or anhydride:
59
(4) RCOC1 R-NH + RCONHR + HC1 (2-4) 2
(RCO) D+ li-NH2---+ RCONHR + RCO
2H
Amides may also be formed:
(2-5)
(5) .RC RCONH2 (2-6) N + H2O
The hydrolytic conversion of nitriles to amides may
in some cases be brought about by the action of
hydrogen peroxide on the nitrile in alkaline solution:
RCN + 2H202
RCONH2 + 0
2 + H2O
The mechanism of this rather curious reaction has
been established by Wiberg. 119
tt (NH4)2 Sx
3 H2O (6) Ar-C - CH
(2-7)
Ar-CH2-CONH
2 (2-8)
Where(NH4)2 Sx is ammonium polysulphide.
(7) RCOCHN + NH diazok2etone3
RCH2CONH
2+N
2 (2-9) colloidal Ag
2.1.2. Basicity. and Acidity of Amides
The amides, in contrast to the amines, are
very weak bases and only form salts with strong acids,
which are largely. hydrolysed in aqueous solution.
Some amides form salts of anomalous composition; thus
the hydrochloride of acetamide loses hydrogen chloride
60
and gives a salt (CH3CONH)2,HC1 which is more stable
and can be recrystallized from ethanol. The N-alkyl
amides are more strongly basic and form stable
platinichlorides. On the other hand, the amides have
slow acidic properties and can give rise to salts with
metals. If acetamide in benzene is heated with potassium,
hydrogen is evolved and potassium acetamide crystallizes.
A convenient method of obtaining such salts is by the
intereaction of an amide with sodamide or potassamide.
These salts are completely decomposed by water or
ethanol. In liquid ammonia as solvent, the amides
are distinctly acidic (in the Lowry-Bronsted sense)
and neutralization reactions of the following type
occur:
RCONH2 + gH
2 ----p RCONH + NH
3
Acid 1 Base 2 Base 1 Acid 2 (2-10)
The secondary amides, for example, diacetamide
(CH3CO)
2 NH, M.P. 79
0 C, show no basic properties but,
as would be expected, their acidic character is more
marked than with the primary amides; the sodium salt
of diacetamide is stable in alcoholic solution.
Because of the electron density shift from the
nitrogen to the oxygen in amides, protonation of
amides in acid solution occurs predominantly at the
oxygen and not at the nitrogen. This is confirmed
by physical methods, especially proton magnetic
resonance.120
The cation has the structure (I):
61
O-H O-H
4 R-C or R-C
NH2
NH2
(I) (a) (b)
The amides anion of the metallic amide salts has the
structure (II):
R-C \ NH
0 0 9
or R-C r., R-C / \ CV
NH NH
(a) (b)
The formation of the amide cation by protonation of
the amide reduces, by the formation of the new
covalent bond, the number of unshared electrons
available to take part in delocalisation from six
to four, so that the resonance stabilization energy
in the cation is presumably somewhat less than in the
free amide. Conversely, the formation of the amide
anion by abstraction of a proton from the amide
increases the number of unshared electrons available
from six to eight, so that this stabilization in the
anion is somewhat greater than in the free amide.
Thus the observed reduced basicity and increased
acidity of the NH2COR system as compared with those
of the simple amines NH2CH2R is to be expected.
62
• 2.1.3. Hydrogen Bonding
In the solid state, it has been shown by
both infrared121
absorption studies and by X-ray crystal
analysis122
that amides undergo extensive intermolecular
-N-H----O hydrogen bonding. The X-ray results show that
the crystals of several simple amides consist of extended,
slightly deformed sheets of amide molecules linked by
hydrogen bonds.122
The somewhat anomalous physical
properties of the amides are clearly related to this
hydrogen bonded polymeric structure. As noted above,
the infrared absorption spectral studies have indicated
that the intermolecular hydrogen bonding found in the
crystal of amides persists to some extent in the liquid
and in concentrated solutions. These deductions are
confirmed by the lowering of the boiling point
accompanying the successive introduction of alkyl
groups on the N atom in the series, and by molecular
weight studies in benzene solution which reveal
association 1.23,124
2.1.4. Alkylation of Amides
Amides present three possible sites for
alkylation. The oxygen and nitrogen centres in the
amide function and the carbon atom at the 0( - position.
Examples of all three types of reaction are known.
However, amides are weak nucleophiles and intermolecular
alkylation under neutral conditions takes place slowly
and requires active alkylation agents, such as trialkyl-
oxonium salts125
or dialkyl sulphates.126
Under these
circumstances alkylation, like protonation of amides,
occurs predominantly at oxygen affording imidates.
Presumably the reaction involves the intermediate A,
rather than intermediate B, since A is more stabilized
63
by delocalisation. + )
OR OR 2 2
RiCONH2 + R2 04- -----4
3 R1 -6:P.:.:NH 2 —4R1-C = NH
(1-1
)
A R1 -C-NH
2R2
(2-11)
On the other hand, alkylation of the anions generated
from amides by treatment with a suitable strong base
leads to N-alkylated products. In this case both of
the possible products of alkylation at 0 or N are
neutral molecules and the course of reaction is
controlled by the greater nucleophilicity of the
nitrogen centre:
0 _ R2X R.-CONH2
+ B [R1
RCONHR2 1
(2-12)
X4,
OR
R-C = NH
Thus a number of N, N-dialkylamides have been
prepared in 60-90% yield by successive treatment of
the monoalkyl compounds with sodium hydride in toluene
followed by Alkyl halide.127
Sodamide, lithium amide
or sodium have also been used as a base for the generation
of amide anions.128
When N,N-dialkylamides are treated with a strong
base and an alkyl halide, alkylation occurs at the ix-
position via carbanion intermediates:
- - R2
2
X
2 RCH--CONA
2 + B RCHCONR
2 -----4 R-CH-CONR.
I R
(2-13) 2
64
In unsubstituted or N-monoalkylamides, C-
alkylation competes effectively with N-alkylation only
when there is some special structural feature of the
molecule which enhances the acidity of the o(-hydrogens
as, for example, in acetoacetamide. However, some
secondary amides are converted into their C- and N-
dianions when treated with butyllithium and subsequent
alkylation then occurs, preferentially at the carbon
centre:129
Li Li BuLi
PhCH2Cl
CH3-CONHPh -----4' CH
2 -CON-Ph
Li
PhCH2CH2CONHPh
H2O PhCH
2CH2CONPh
(2-14)
N-alkylation is conveniently achieved by treating
a lactam successfully with sodium hydride and an alkyl
halide in benzene. This method has been used for the
methylation of large ring lactams130
and for the
preparation of the interesting allenamide by spontaneous
rearrangement under the reaction conditions of the
initial acetylenic product:131
L ,]=0 + BrCH2C CH NaH
F
= CN)
CH2-C=7CH
N = 0
CH2=C=CH2
H
L /I= 0 + 2NaNH + 2MeI 2
CH3
4LN = 0 (2-16)
Me
j Me
65
N-Methylpyrrolidone can be converted into the 3-
methyl derivative by successive treatment with sodamide
in liquid ammonia and methyl bromide.132
When an
excess of reagents was used dialkylation occurred:
Me
2.1.5. Photochemical Reactions of Amides
(A) Photolysis of Amides
Photolysis of amides and lactams has been
studied by several authors. The results obtained in
the photolysis of acetamide133
in the vapour phase
involve the primary processes:
CH3-CONH
2 hv
CH3 + CONH2
(2-17)
CH3-CONH
2
by CH
3-CN + H2O (2-18)
It has been shown by e.s.r. spectroscopy that the
primary free-radical producing step in the photolysis •
for formamide134
is the formation of H and CONH2.
Substitution of a methyl group on the nitrogen atom
in these compounds does not change the essential
nature of the primary step.
66
(B) Photoamidation
The photoaddition reactions of formamide to
olefins, acetylene and aromatic systems have been
studied.135,136 These reactions involve the addition
of formamide to the double bond yielding higher amides
and are usually initiated photochemically by aceton,
acetophenone or benzophenone. For example: 137
hv RCH = CH
2 + HCONH2 ------* RCH 2
-CH 2 -CONH
2 ketone 2
The reaction with terminal acetylene leads to 2:2 adducts
as the major product
hv CONH 2
R-C = CH + HCONH2 ketone R-CH-CH-CONH
2 CH=CHR (2-19)
but non-terminal isolated acetylenes yield 1:2
adducts under similar conditions:139
hv RO2C-CHCONH2 RO
2C-C=C-00
2R+2HCONH
2 R=CH3'C2H5 R02 C-CHCONH2 (2-20)
RCH = CH + CH3CONHCH
3 hv (2-21) acetone
67
The addition of formamide to olefins and dienes can
also be induced by Y.-rays and electron irradiation.140,141
N-Methylacetamide reacted with olefins under U.V.
radiation in the presence of acetone to give substitution
products:142
CH32 CONHCH-- (CH
2 )2 R + R (CH
2 ) 2 --CH
2 CONHCH
3
major product minor product
(C) Photo-oxidation of Amides
Photo-oxidation of amides has been studied by
several authors. Sharkey et al143 reported that the
photo-oxidation of N alkylamides yielded aldehydes,
acids and amides. Formation of these products
indicates that photo-oxidation involves oxygen attack
on the methylene group adjacent to nitrogen. The
mechanism involves the production of RCONHCHR radicals:
hv RCONHCH
2 RA > RCO + NH-CH
2- RI
•
RCO + RCONHCH2R1 ------4 RCHO + RCONHCHR 1
(2-22)
(2-23)
R1 CH
2 I\TH + RCONHCH2
R1 RICH2NH2 + RCONHCHR1 (2-24)
Followed by propagation:
0. RCONHCHR1
+ 02 > RCONHCHR 1
0-OH 9-0. 1
RCONHCH-R1 + R-CONHCH2R1 ----"4 RCONH-CHR
• 1 1
+ RCONHCHR 1
(2-25)
(2-26)
68
and many other reactions, including termination. Lock
et a1144 reported similar oxidation processes using
photoinitiators such as 2-methyl-anthraquinone.
2.1.6. Radiation Chemistry of Amides
The radicals formed on irradiating solid amides
are usually stable and can be detected by their electron
paramagnetic (spin) resonance. The radical yields are
expressed as G values, which are the number of radicals
formed per 100 e.v. of energy absorbed. In diluted
solution the radicals initially formed are from the
solvent molecules and these radicals then attack the
amides present in the solution. The e.s.r. spectra
of acetamide initiated by X-ray showed the presence
of *CH2C0NH
2 radicals
145 and N,N dideuteroacetamide
(CH3COND
2) gave an identical spectrum.
146 Also
the e.s.r. spectra of acetamide irradiated with 1
Mev electrons also indicated the presence of the
CH2C0NH2 radicals.147 Trimethylacetamide, which
has no free hydrogen on the /9-carbon atom, gave a
(CH3 C radical. A number of similar studies have
been reported on N-alkylamide.147
In all cases
the radicals were formed by loss of a hydrogen atom
from carbon and the loss occurred from an N-alkyl
group in preference to the acyl group.
2.1.7. N-Chlorination of Amides
Both molecular halogens (other than fluorine)
and hypohalites behave as ionic halogenating agents
toward primary and secondary amides. The usual product
69
is the N-haloamide, although in a few instances carbon-
substituted derivatives are also obtained. This can
be associated with the instability of the N-haloamides
and their composition in acidic solutions to give
'positive' halogen, which may then attack other parts
of the amide molecule:
4 0 RCONC1Ph H 1"- a
> R-C 4 •NHPh 4_____ --1' RCONHPh + XCl (2-27)
b X IC
CP-
RCONH - Q + X
(0,P, isomers)
Thus primary and secondary amides react with chlorine
to give N-chloro amides. The overall reaction is
reversible and the equilibrium position depends on
the solvent. Highly polar solvents, for example,
water, favour N-haloamide formation:148
RCONHR1 + Cl
2 ----4 RCONC1R
1 + HC1
(2-28)
(R1 = H, alkyl,aryl,etc)
Hypohalites are preferable to molecular halogens
for preparing N-haloamide because competing halogenation
of C-atoms is less of a problem. Hypohalous acids are
Cl
70
usually formed by adding an equimolar amount of sodium
hydroxide to a mixture of the molecular halogen and
the amide:149
RCONHR X2+NaOH HOX+NaX ------4 RCONXR
1+H2d •
(2-29)
(R1 = H,alkyl, Ph, etc.)
Various secondary amides have been N-chlorinated at
different pH by Tomm et al•150
The substituent groups
R1 and R
2 of the amide R
1-C-NHR
2 were found to have
large effects on the rate of chlorination. The present
discussion illustrates the effects of substituents R1
and R2 on the reactivity of the secondary amides, 11
R1CNHR
2 towards the different chlorinating agents.
Following Mauger and Soper151
the reaction may be
written: H 4-- X
if R1 -C -N---C1
2
Where X may be Cl HO, ACO or O. Mauger and Soper151
suggested hydrogen bond formation between the amido
hydrogen and the X group. The rate of reaction of the
chlorinating agent and the amide was dependent upon
the ease of formation of such a bond. The readiness
of such bond formation depends on the nature of R1
and R2, which determine the electron density about the
amide N ,and thus the strength of the bond between the
NH group and the chlorinating agent.
R
71
The carbonyl group has a high electron affinity.
The electron donor properties of the andd R2 groups
in part determine the electron density about the amide
N-atom. The higher the electron donating power, the
more electronegative the amide N-atom, the stronger
NH bond and the lower the expected rate of reaction.
2.1.8. Rearrangement of N-Chloroamides
N-chloroamides can be photolytically re-
arranged, but the resulting 4-chloroamides are far
less readily cyclized than the bromo analogues. In
fact, both N-chloroamides and 4-chloroamines are
now sufficiently stable for facile isolation and
purification.152
hv, solvent,25oC
R1CH2-CH
2-CH
2-C-N-R2 R-C-CH
2-CH2-C-N-R
24
0 Cl Cl 6 h (2-30)
R1 -CH
2 -CH
2 -CH
2 -C-NHR
2 (4-chloroamide)
0
(Formed by H-abstraction from the solvent)
• 4-chloroamides on heating in aqueous acids give
%lactones with elimination of halogen halides.
2.1.9. Na/NH3
If alkali metal is added to an excess of
liquid ammonia, a deep blue colour immediately appears.
If more alkali metal is dissolved in the ammonia,
72
eventually a bronze coloured phase separates and floats
on the blue solution. Cesium appears to be an exception
since a two phase system is never obtained. Further
addition of alkali metal results in the gradual
conversion of blue solution to bronze solution until
only the bronze solution remains. Unchanged alkali
metal may be recovered by evaporation of the ammonia
from the bronze solution. This unusual behaviour has
fascinated chemists since its discovery. The following
simplified discussion will indicate a reasonable
interpretation.153
The blue solution is characterized by:
(1) its colour which is independent of the
alkali metal involved;
(2) its density which is less than that of
liquid pure ammonia;
(3) metal-ammonia solutions are extremely
good conductors of electricity, for
example, the specific conductance of a
standard sodium solution at -33.5oC
is 5047 mhos cm, that for mercury at o .
I -1
0 C s 10600 mhos cm;
(4) its paramagnetism indicating unpaired
electrons and its electron paramagentic
resonance "g-factor" which is very close
to that of the free electron.
73
This has been interpreted as indicating that in
diluted solution, alkali metals-dissociate to form
alkali metal cations and solvated electrons: dissolved in
MNH3
> M + ( e (NH3)]
The dissociation into cation and anion accounts for
the electrolytic conductivity. The solution contains
a very large number of unpaired electrons, hence the
paramagnetism and the g-factor value indicates that
the interaction between solvent and electrons is
rather weak. The electron is suggested to exist in
a cavity in the ammonia, loosely solvated by the
surrounding molecules. All metal-ammonia solutions
are metastable. If they allowed to stand for long
periods, or if suitable catalysts are present,
decomposition to hydrogen and the metal amide
occurs:
[e (NH3)x ] ------4 NH2+11 H2+ (x -1)NH3 (2-32)
The bronze solutions have the following character-
istics:
(1) a colour with a definite metalic lustre;
(2) very low densities (a saturated solution
of lithium at room temperature possesses
a density lower than that of any other
known liquid at the same temperature);
(3) conductivity in the range of metals;
(4) magnetic susceptibility similar to those
of pure metals.
(2-31)
74
All of these properties are consistent with a
model describing the solution as a "dilute metal" or
"alloy" in which the electrons behave essentially
as in a metal, but the metal atoms have been moved
apart (compared with the pure metal) by interspersed
molecules of ammonia.
75
3. REVIEW OF PREVIOUS WORK
3.1. Introduction
One of the reasons for the steady growth of
the nylon plastics industry is the facility with
which the structure of a nylon can be altered for
different purposes. Diamine, diacid, amino acid
and lactam intermediates can be combined almost
at will to provide a variety of homopolymers and
copolymers. Also, to a given nylon different
materials can be added, either by simple blending
or chemical interaction to yield desired processing
behaviour, improved stability, or other specific
properties. In industry different additives have
been used for modification of nylons, such as
antistatic agents, fillers, plasticizers, pigments,
stabilizers, etc. Many modifying agents can change
more than one property. For example, plasticizers
normally retard the rate of crystallization, so the
side effects of modifying agents must be considered.
Since modification of nylons through chemical reactions
is more related to this research, mainly this topic
will be reviewed in this chapter.
3.1.2. Nylon Copolymers
Polyamide copolymers often have lower melting
points and are more soluble than the corresponding
homopolymers. This is believed to be because the
degree of crystallinity is reduced and the regularity
of appearance of amide groups is disturbed, which can
reduce the incidence of hydrogen bond formation
76
between adjacent chains.185 However, if the disorder
is not great, the copolymer will have properties
intermediate between the possible homopolymers.
3.1.3. Reactivity of Nylons
Nylons have excellent resistance to chemicals
in normal usage; but nylons can be made to participate
in a variety of reactions. The site of attack may
be anywhere in the molecule, depending on the nature
of the reaction. For example, the end group, the
amide nitrogen, the amide carbonyl or the hydro-
carbon portions may be attacked. In Table (3-1)
useful reactions have been mentioned. Attempts
have been made to minimize the effects of undesirable
reactions such as photolysis or oxidation, by
suitable modification.
186 TABLE (3-1)
REACTIONS OF NYLONS
Site of Attack Reaction Purpose
-COOH, -NH2
0 H -C-N-
2 -C-N-
-CONHCH-
Salt formation or reaction with mono-functional, groups.
Alkoxyalkylation
Hydrolysis
U.V. and atomic irradiation in the presence of a vinyl monomer.
Determination or control of mole-cular weight.
Lower crystallinity increased solubility and permit cross-linking
Regeneration of intermediates.
Grafting to alter properties.
77
3.1.4. Nitrogen Substituted Nylons
Polyamides, such as nylon 6, nylon 66, nylon
610 and nylon 12, exhibit properties which are largely
due to their molecular order and the high degree of
inter-chain attraction which is a result of their
ability to undergo hydrogen bonding. It is,
however, possible to produce polymers of different
properties by replacement of some or all of the
-CONH- hydrogens by alkyl or alkoxyl-alkyl groups
to reduce hydrogen bonding.
Elimination of the hydrogen atom on the amide
nitrogen destroys hydrogen bonding and brings about
lower stiffness, lower melting
solubility.187-190 The degree
the degree and distribution of
point and increased
of change depends on 188,189
nitrogen substitution.
For example, the melting point of a 40% N-methylated
nylon 66 (based on numbers) is 210oC if the polymer
is made from a 60/40 mixture of hexamethylenediamine
and N N- dimethylhexamethylene diamine, and 185oC
if made from a 20/80 mixture of hexamethylenediamine
and N-methylhexamethylenediamine. The use of a
diacid with a sufficiently long methylene chain can
lead to a crystallizable nylon, even if fully
alkylated,191 N. N dimethylhexamethylene diamine
and octadecanedioic acid yield a crystallizable
nylon. The polymer has repeating units of the
general form:
) - (CH2n I
78
Such N-alkylated compounds are not known to be
of any current application although fibres from a
partially N-alkylated derivative of nylon 610 have
been described.
N-substitution can be brought about by reaction
with the polymer as well as by polymerization
involving N-substituted diamines. In Table (3-2)
the preparation of N-chloro nylons is described.
Treatment of a nylon with formaldehyde leads to the
formation of N-methylol groups - Table (3-3,4) -
but the polymers are unstable. If, however, the
nylon is dissolved in a solvent such as 90% w/w
formic acid and then treated with formaldehyde and
an alcohol in the presence of an acidic catalist,
suchas phosphoric acid, a process of alkoxymethylation
occurs:
L NH N-CH2OR N(CH 0) R
COCO// 4- CH201-ROH /
COor / 2 2
\
Methyl-methoxyl nylons are commercially available
in which about 33% of the -NH- groups have been
substituted.
Such materials are soluble in the lower aliphatic
alcohols, for example, ethanol and in phenols. They
also absorb up to 21% w/w of moisture when immersed
in water. If this material is heated with 2% w/w
citric acid at elevated temperature, typically for
20 minutes at 120°C, crosslinking will take place;
(3-1)
79
H+ 1 1 I I
N -CH2 OCH + NH ----÷ N -CH -N + CH OH 3 2 , 3
CO CO CO CO (3-2)
These materials find a limited application
for films and coatings which require good abrasion
and flexing resistance.
TABLE (3-2 N-CHLORO NYLONS
Nylon Chlorination Reagent '
Experiment •
Reference .
Result
6 (i) t-Buocl (i) Tetrachlore.thane was used as solvent. The
183,184 The conversion degree of substitution determined
reaction was done at 15oC • by iodometry reached
' for 3 hours over 95%. Suitable
• 66 (ii) KoC1 in (ii) Chlorination was in chlorination agents were
• H20 2
aqueous media for 3 hours (i) and (iv). The N- polymers
3. (iii) Cl2+KHCO
3 (iii) A solution of tetra- chloroethane which
readily oxidized second-ary and primary alcohols
(iv) Cl 0 in contained KHCO, was used in the same manner as
, 2 CC14 and a stream a' Cl
passed through the2solut-
ion. The reaction was imides.
low molecular weight N-halogenated amides and
performed at 15°C for . . 3 hours.
(iv) Nylon was suspended in tetracholoroethane and
a solution of C120 in CC1
4 was used. •
• . .
oz)
TABLE (3-3) - PREPARATION OF ALKOXYL-ALKYLATED NYLONS
Nylon Monomer Experimental Condition
•
Reference Result
12
.
HCHO
.
A solution of 100g nylon 12 in 100g paraformalde- hyde and 170g Ms0H was mixed with 10cm Me0H containing 2g H1POA and kept 30 mins at 00 C-
167
.
.
.
The yield is a liquid product, stable at room temperature.
.
.
TABLE -4 - PREPARATION OF ALKOXYL-ALKYLATED NYLON
Nylon Monomer Expe'rimental Condition •
Reference Result •
Polycapro- lactam
w-Capro- lactam W-lauro lactam :opolymer
HCHO
Paraformalde- hyde
.
.
Polycaprolactam was hydro- xymethylated with a pyr- idine :formaldehyde sol- ution under pressure at 100
o-140
oC
The copolymer was dissol- ved in a mixture of 20g paraformaldehyde and 100g of a Me0H-00HC1
3omixture,
stirred at t0-635°C; lg phosphoric acid was added
at that temperature,
•
and heated for 40mins.
169 .
.
/
178 ,
. . .
The change in tear strength and M.P. was small.
A N-methoxymethylated copolyamide was obtained
. ,
.
•83 n
3.1.5. Graft Copolymers of Nylons
Graft copolymers of nylons can be synthesized
through polycondensation, radical and ionic reactions.
3.1.5.(A) Polycondensation
Ethylene oxide can be grafted onto nylons
by using the nylon chain as the initiator in the
polymerization of the monomer. The ethylene oxide
treated nylons are described in Tables (3-5,7)
and provide examples in which the -NH7 bond of the
amides serve as initiator:
9 0 fNH(C
H2)'6-NH-C(CH
2)4-6++ m CH
2-CH
2----).,
(3-3) 0 9 01 11
+NH (CH2 )6- N-C (CH2 )4- C3—
I (CH
2-CH
20)
mH
The formation of graft copolymers of novolacs
on polyamide backbones was investigated by Ravve
et al.200 Generally, when the condensation reactions
with formaldehyde are carried out simultaneously
on both phenols and amides, competing reactions take
place.
In the presence of moderately strong acids, like
formic acid, the rate of formaldehyde condensation
with amides was found to be the more rapid than with
phenols. Hence it was found advisable to form novalacs
initially and then to graft these materials onto the
polyamides.
TABLE (3-5) - PREPARATION OF NYLON-g-POLY(ETHYLENE-OXIDE) BY CONDENSATION POLYMERIZATION.
Nylon Monomer Experimental Condition Reference Result
The reaction rate increas-ed following dehydration of the polymer over H2SO4
The oxyethylated polyam- 160 ide was blended with (I)
to give films which had good vapour permeability and medium tensile strength.
One part (II) was mixed with nine parts (I). The antistatic property of (I) was improved by mixing with (II) •
AK (I) (Probably Nylon 6)
Polycapr-oamide
Ethylene Oxide
Ethylene Oxide Polycaproamide (I)2.3Wt2 KOH, and ethylene oxide wee reacted in PhC1 at 80 C for 7 hours to give 162 polyokyethylenated poly-caproamide(II) containing 65% wt ethylene oxide.
TABLE (3-6) PREPARATION OF NYLON -g- POLY (ETHYLENE-OXIDE) BY CONDENSATION POLYMERIZATION
Nylon. Monomer Experimental Condition Reference Resuit
Poly Ethylene Oxide 30 parts by weight of Caprol- Propylene Oxide polycaprolactam and 180 actam parts ethylene oxide
were heated for about 65 hours up to a temper-ature of 150 C. A viscous product was obt-ained
170 Antistatic polyamide fibres were prepared.
. TABLE (3-7) - PREPARATION OF NYLON -g- POLYETHYLENE OXIDE) BY CONDENSATION POLYMERIZATION
Nylon Monomer Experimental Condition Reference Result
181
The general method for preparing hydroxyethyl nylons and related products was by treatment of the polymer with excfs liquid ethylene oxide for 10 - 72 hours in stainless steel bombs at 80 C. Generally, the longer the reaction time, the higher the ethylene oxide conten of the products.
Hydroxyethylated nylons are a class of stable nylon derivatives which are particularly useful when the nylon character coupled with greater flexibility, rubberi-ness and higher water absorption are desired.
66 Ethylene Oxide
t
87
3.1.5.(B) Grafting Copolymerization Through Radical Mechanisms
(a) ■6 , Electrons, U.V. Irradiation and Electric Discharge.
Graft copolymerization can also be done
by exposing nylons to high energy radiation to
generate free radicals and then treating with vinyl
monomers, such as vinyl acetate, acrylonitrile
and acrylates. The site of attachment of the vinyl
polymer to the nylon is the carbon atom adjacent
to the amide nitrogen. These polyvinyl grafts
lead to improved dyability static resistance,
light durability and property improvements that
are especially advantageous in fibres (Tables3-8,12).
Graft copolymers of nylon 6 and acrylonitrile
through electric discharge have been prepared
(Tabla 3-13).
TABLE (3-8) PREPARATION OF NYLON GRAFT COPOLYMERS BY RADIATION METHODS
Nylon Monomer Radiation Experimental Condition Result Reference
66 tyrene inyliden chloride
The rate of grafting is independent of the temp. (20-60 C) and is proport ional to the dose. Nylon 171 66 grafted with vinylide chloride is not fireproo
polyamide acrylonitr ile crylic acid
Capron acrylonitr (Nylon 6) ile
a
Nylon 66 fibres were grafted with styrene and vinyliden chloride in HAOC-H10 solutions which swelled the fibre. Gamma rays from a Cobb source were used.
The fibrous substrate was not irradiated; only the monomer to be grafted passed through the irradiation chamber.
7 megarad Loose, highly oriented dom fro capron threads were Co irradiated with a 7
memrad dose from a Co source in vacuo at 22o C. Then they were
exposed to acrylonitrile vapours at 80mm Hg pres-sure for 5-100 hours.
This method was develope for producing grafts by radiation without the attendant degradation of other methods.
The grafted polymer was free of hoinopolymek impurities.
174
175
6 acrylamide
(Nylon 6) Capron (1 Silk (2) Viscose(3
(Nylon 6) Kapron Natural Silk
styrene Me-methac-rylate
acryloni-trile styrene
1
TABLE 3-9) - PREPARATION OF NYLON GRAFT COPOLYMERS THROUGH RADIATION METHOD
Nylon Monomer Radiatio Experimental Condition Result Reference
I*
The fibre is soaked in a Me0H solution of acryl-amide and then treated with rays.
Styrene could be grafted onto 1,2,3 from an mem solution and onto 2,3 in the absence of a solvent after the fibre had been moistened with H10. Me ethacrylate could be
grafted onto 1,2,3 after the fibre had been moist ened with H2O and aceton
he best solvent for rafting acrylonitrile as H
20 and for grafting
tyrene, ETOH.
Good dyeability. Poly- acrylamide was extracted 157 with water.
The amount of polymer grafted onto the fibres increased rapidly up to a limiting radiation dose 158 t higher doses the rate of increase in weight slowed down considerably. '
Infrared spectra of the rodUcts indicated that 166 he C=N group was intro-uced into the silk and apron
0
TABLE J3-10) - PREPARATION OP NYLON GRAFT COPQLYMERS RV RATITATTOU MPTITO S
Nylon Monomer Radiation Experimental Condition Result Reference
Such grafting resulted in increased wettability of the fibre at 1% w/w polystyrene and a decrea- 176 se at 2% w/w. The diff-erences with a greater proportion of the graft were relatively small.
Polycapro styrene lectern
(nylon 6)
.%1 Polystyrene was surface grafted on poly-capro-lactam fibres in ne gas phase by using CO initiation.
Irradiation of nylon Styrene and Me methacry-66 Me methacrylate, and late are grafted directly styrene in the presence onto the polyamide chain 177 of Me0H containing approxto produce fibres having 10% v/v water gives good tersile strength, graft copolymers. water resistance, radiat-
ion resistance, antistati' properties and dyeability
66 Me methac-rylate styrene
Nylon Monomer Radiation Experimental Conditions Results Reference
TABLE (3-11) PREPARATION OF NYLON GRAFT COPOLYMERS BY RADIATION METHODS
Nylon particles were ground and soaked in the monomer (I). This slurry was vacuum dried, irradiated and resoaked for 3 hours in an aqueous solution of (I)
(I) was grafted onto (2) fibres by U.V. irradia-
tion of the components in Me0H containing B.zZO2 or AIBN.
Radiation synthesis of graft polymers in the gas phase.
66 -vinylpyr-rolidone (I)
electrons
Kapron(2)
(Nylon 6)
styrene(I) U.V.
acrylonit-dose inte- nsity
styrene 50. rad/sec
Me metha-: crylate (The
source is not defin-ed.)
polyamide polyethy-lene polypoy-lene
Nylon 66 grafted with 24.4% w/w. (I) possessed a good distribution of 154 grafts from surface to core.
Polystyrene was isolated as a by-product. The tensile strength of the grafted product was lowe than that of unreacted Kapron due to partial radiation degradation which also occurs during grafting.
The grafting of vinyl-type monomers is of the radical type and that th velocity of the grafting reaction depends on the conc.of the monomer in the sorption layer on th surface of the polymer.
155
156
•
TABLE (3-12) PREPARATION OF GRA
Nylon Nonomer
6 styrene
6 styrene
Radiation
light of wavelength). 300nm
Hg lamp ( A) 300nm)
Experimental Condition
In the absence of solven ~rafting proceeded only ·slightly except at a temp
o 0 bove 60 C. At 25 Conly eOH has a marked accelrating effect on the rafting and the max.
effect occurs at w 30% 01. of the monomer. EtOH,
PrOH and BuOH also acc~l rate the grafting.
on-sensitized graft poly erization of styrene to ylon 6 fibres was 'carrie ut mainly at 2S
oC in the
resence of MeOH, using utual irradiation techique. In the case of a igh pressure Hg lamp, he presence of oxygen, 'f not excessive, accelrated the polymerization n the case of a W lamp, raft copolymerization nly occurred in the resence of limited
quantities of air.
Results
The alcohols are not responsible for the initiation of grafting, but are necessary for penetration of monomer into ,the inner regions of ,the nylon.
These results showed that oxygen both inhibi and initiates the graft copolymerization •.
Referenc
159
180
\.0 N
TABLE - PREPARATION OF NYLON GRAFT COPOLYMERS BY ELECTRIC DISCHARGE
Nylon Monomer Initiator Experimental Condition Result Reference I •
The graft copolymeris-ation of acrylonitrile vapour on cotton and nylon 6 fibre after activation on the fibre by an electric discharge in Ar gave good results
The amount of homopoly-merized acrylonitrile obtained in the reaction was small compared with other grafting methods.
6 acrylonit- electric rile discharga
161
94
(b) Chemical Methods
Besides grafting initiated by high energy
radiation, chemical methods include the use of
persulphates and ceric salts as initiators. Grafting
onto nylon peroxidised by ozone192,193
is also
successful, whilst in irradiation - grafting conducted
in the presence of air - peroxide groups formed on the
nylon are, at least, partly responsible for initiation.
Although there is little published information on the
oxidation of Nylon 66 by a free radical mechanism, it
seems quite reasonable that the mechanism be similar
to simple N-alkylamides.
The reaction of potassium persulphate with
several amides of varying substitution in an oxygen
free system has been studied. Aqueous solutions of
persulphates decompose to yield sulphate and hydroxyl
free radicals.194
Attack of N-methyl in N,N 195-197
dimethylamides by free radicals also has been observed.
This suggests that the dealkylations proceed via radical
attack on the carbon on to the amide nitrogen. Initiation
and transfer steps can be shown as follows:198
•
-2 - 2S50
4
+ OH
0 HSO4 -I - R-C- - N-CH
2
(3-4)
. (3-5)
(3-6)
5208
SO4, + H2O
0
So° + R-C-N 4
'
-CH3
HSO4
CH3
CH3
0 _ H2O R-C-N-CH OSO 2 3 H'
CH
0 11 R-CNHCH3 +
3 (3-9)
95
0 0 OH + R-C-N-CH3 -----* 2 H20 + R-C-N-CHe (3-7)
CH3 CH3
0 0 u o -2 11 _
R-C-N-CH2 + S208 ----)•-R-C-N-CH 0 + SO'
4 (3-8) , 1 CH3 CH3
(1)
The anion (1) decomposes as follows:
0 11
H-C-H + HSO 4
So it appears that primary attack occurs principally at
the methylene group adjacent to the amide nitrogen with
potassium sulphate. Although there is not much
information of amides being oxidised by ceric salts by
analogy with oxidation by persulphate attack at the
methylene group adjacent to amide nitrogen is probably
favoured. The radical thus formed would thep initiate
polymerisation or undergo further oxidation to an enamide,
followed by hydrolytic chain-fission to primary amide
and aldehyde end groups. Oxidation of the aldehyde, again
by a free radical mechanism, would finally yield carboxyl
end groups.199
96
CH2-CO-NH-CH2-CH2 Ce+4 (3-10)
CH2 Ce+4
-CO-NH-CH-CH 2 (3-11)
CH2-CO-NH-CH=CH H2O H+
(3-12)
CH2CONH2 + OHC-CH2 (3-13)
+4 CH2CHO 2ce CH2COOH (3-14)
97
In Tables (3-14) to (3-17) some typical
examples of grafting nylons initiated by chemically
produced radicals are briefly described.
3.1.5. (C) Ionic Synthesis
Polyamides have been largely neglected as
substrates for the ionically-initiated grafting of
vinyl and epoxy polymers. However, in Table (3-18)
the previous ionic grafting of nylons i5 described.
Reference Nylon Monomer Initiator
66 styrene (NH4)2S20 A grafted taffeta was
prepared but few details 163 are available
Nylon 6 taffeta after heating in H20 was treated with a (NH
4 )2 S2 08 a 0 aueous
solution at 50 C. After drying the taffeta was heated with excess styrene.
Experimental Condition
179 6 acrylonitr(NH4)2S20 ile
Translucent strong fibres were prepared.
Acrylonitrile was grafte onto nylon 6 in HNO3 in the presence of (NH
4)25208,.FeS0
4 and
acetylacetone.
Results
TABLE (3-14) - PREPARATION OF NYLON. GRAFT COPOLYMERS BY CHEMICAL METHODS (RADICALS
TABLE (3-15) -.PREPARATION OF NYLON COPOLYMERS BY CHEMICAL METHODS (RADICALS)
Nylon Monomer Initiator Experimental Condition Result Reference
66 acrylic acid I Ce (iv)
11 acrylamide
-6 Nylon films 4-6 X 10 m thick were prepared from solutions of nylon in a mixture of HCO0H, H00 and concentrated Htl. The nylon 66 films were cast on glass, washed with H 0 and then
2 treated with a 10% v/v solution of acrylic acid and 0.01M (NH4)4 Ce(SO4 - 0.2N HoS0A. Poly-acrylamide was grafteid onto nylon film by treating the film with a 10% w/v solution of acrylamide in a solution of 0.01M (NH
4')2 Ce(NO
3)6
in 0.6N
HNO3.
An infrared deuteration study of the grafting reaction showed that it occurred in all the regions of the nylon 66 accessible to D
20.
173
TABLE (3-16) - PREPARATION OF NYLON GRAFT COPOLYMERS BY CHEMICAL METHODS (RADICALS)
Nylon Monomer nitiator Experimental Condition Result Reference
6
6 Ce (iv)
Acrylamide Acrylonit-rile
Acrylonit rile Styrene. Acrylic Acid
Graft copolymerisation of acrylamide and acryl-onitrile onto nylon 6 swollen in formic acid was performed using Ce (iv) ions as initiator at 60
oC.
Nylon 6 fibres were soaked in a K
2S208
solution. After dissol-ving in HCOOH the nylon was precipitat ed,centrifuged and exposed 1 hour to CH2 = CHCN vapour
The physical properties of the grafted nylon 6 were studied.
Weight increase of treat ed nylon 6 fibres were 61.7 - 137% w/w. •
168
172
TABLE (3-17) - pREPARATION OF NYT,ON GRAFT COPOTWMPRS RV CHRMTCAT. MPTHODS (RADTCALS)
Polymer Monomer Initiator Experimental Condition Result Reference
N-halo-genated amide Nylon 66
Metal carbonyls mercury lamp
methyl methacryl-ate methacryl-ic acid acryloni-trile styrene vinyl ace tate
The carbonyls differ widely in their initiat-ing activity; thus, Mo_(C0)6 is effective at 80
o' C, while C64 (CO )12
initiates at 0 C. Tie nature of the halide component of the initia-ting system also has an important influence on the rate of polymeriz-ation.
First, all the compounds form active initiating systems with molybdenum carbonyl at 80 C. Second, some, of the N-halogenated derivatives, when used in sufficiently high concen-tration, may be quite active initiators in the absence of the carbonyl.
164
TABLE (3-18) - PREPARATION OF NYLON GRAFT COPOLYMER BY IONIC REACTIONS
Nylon Metalatior
Monomer Agent Experiment Result Reference
6 acrylonitr alkali The grafting was done i The grafting of acrylo- ile methoxide T.H.F. nitrile on the metalated
e.g. lith fibres increased with ium meth- the monomer conc. in oxide THE but gave a max. at
40-60% v/v monomer in Me2 SO. The metalation
reactions were endother-mic and heats of reacti decreased in the order:
• ILi>Na)Ko
8 ethylene NyNH3 The reaction was done Nylon grafted with oxide in a high pressure ethylene oxide was
glass tube fitted with prepared a valve.
165
182
1
103
4. EXPERIMENTAL
4.1. Apparatus
4.1.1. The High Vacuum Line
The sensitivity of ionic polymerization to
air and water necessitate the use of a high vacuum
apparatus. Figure (4-1) shows the high vacuum line
which was used in this work. The apparatus was made
of Pyrex glass and stopcocks in the main pumping
system were lubricated with Apiezon "N" high
vacuum grease and the others with silicone grease
(Edwards). Silicone grease can be affected by
solvent vapour, so exposure of silicone grease
to solvent vapours was minimized as much as
possible. Chloroform was used to clean the taps
and frequent regreasing was necessary. Splash-
heads were used in the purification system.
4.1.2. Metalation Vessel
A metalation vessel, Figure (4-2) was
formed from two separate parts, I and II, which
could be joined by a cone and socket.
Part I
Part I was made of Pyrex tubing and H was
a 3mm high vacuum tap. Initially, F was a sintered
glass disc with porosity 2, but later it was found
104
that during cooling and warming, cracking of the
apparatus occurred. Hence, finally, the sintered
glass disc was satisfactorily replaced by another
disc which contained fewer holes, Figure (4-3).
D was a long tip cone.
Part II
A was made of 4mm thick high pressure glass
tubing which could tolerate a pressure of up to
1; 3-:xio+Nm
2 and was joined to a capillary with
an inside diameter of 3mm. B and D are 824 sockets
which are joined to the copillary tube.
For injection of DMF after metalation
had been performed, an additional part, Figure
(4-4) was joined to part B of the vessel.
4.1.3. Thermal Analyser
Thermal analysis was performed by a Du
Pont Thermal Analyser with a DSC cell attachment.
Instructions were followed according to the manual
and analysis was carried out in air and an empty
pan was used as reference. Recorded temperatures
were corrected according to the manual.
4.1.4. IR Spectrophotometer
Infrared (IR) spectra of all samples were
recorded with a Perkin-Elmer Model 15'./G Grating
Infrared Spectrophotometer. A film of polymer
or a KBr disc of polymer was used.
105
4.1.5. Centrifuge
A MSE High Speed 18 Refrigerator Centrifuge
at 30oC was used for all experiments.
4.1.6. Apparatus for the Determination of Polyethylene Oxide
An apparatus for the analysis is shown in
the scale diagram Figure (4-5). It consists in
part of the reaction flask, condenser and first
absorption tube of a Clark alkoxy apparatus.203
These are followed by an absorption tube, D, made
from a section of a spiral from a Widmer distilation
column. The detailed dimensions of the apparatus
are described elsewhere.201,203
4.1.7. Viscometer
Limiting viscosity numbers were determined
using an Ubbelohde viscometer fitted with a
pumping device as shown in Figure (4-6). All
the solvents and solutions were filtered directly
into the viscometer under pressure of nitrogen.
4.2. Purification and Preparation of Reagents
4.2.1. Nylon 66
log of nylon 66 (Maranyl A100 Natural
035 I.C.I. Plastic Division - Welwyn Garden City,
Herts.) was dissolved in 60cm3 Analar formic
acid. For precipitation the solution was poured
106
in 250cm3 methanol and finally 250cm
3 distilled water
was added after 2 hours. It was then filtered by
means of a sintered glass funnel (porosity 3) and
the solid was wahsed three times with distilled water.
Benzene was added to a round bottomed flask containing
solid nylon and the flask was then heated. The benzene/
water azeotrope was distilled off through a distilling
column until the distillete was clear. The flask was
connected to the vacuum line and the residue benzene
was condensed into another flask. The the flask
containing the nylon sample was warmed by means of an
IR lamp for 2 hours. The nylon sample became lumpy,
which meant that trace of water or solvent could be
trapped. To.avoid this, the previously dried nylon
was ground, passed through a fine sieve and subsequently
dried in vacuo for about 2 hours while being irradiated
with an IR lamp.
4.2.2. Tetrahydrofuran
THE (Kock-Light, puriss grade) was stirred
over powdered calcium hydride for at least 24 hours
before being fractionally distilled. The middle
fraction was collected and about 50cm3 of the solvent
was left in the distillation flask to avoid a build-
up in the concentration of peroxide in the residue.
The solvent was degassed on the vacuum line over some
powdered calcium hydride and theldistilled into another flask
containing sodium-potassium alloy. It was stirred over the
107
alloy for 3 hours at room temperature. After
degassing again, the THE was distilled into the
reaction vessels for further experiments, or it
was stored in a sealed vessel in the dark.
4.2.3. Ethylene Oxide
The ethylene oxide gas (Cambrian Chemicals
99% w/w pure) was passed through the tube filled
with B D H molecular sieves type 4A Figure (4-1).
The ethylene oxide was collected over a sodium
mirror in a flask cooled in liquid nitrogen, which
was connected to the vacuum line. The ethylene
oxide was stirred over the sodium mirror at 0oC
for about half an hour before it could be used for
any reaction. Quantities of ethylene oxide were
measured by distillation into a calibrated tube
Figure (4-7) maintained at 0°C.
4.2.4. Sodium
A piece of freshly cut commercial sodium
was immersed into two beakers containing petroleum
ether of b.p. 80-100°C and 50-60°C respectively,
in order to remove the protective layer of liquid
parrafin covering the metal. For preparation of
Na /NH3 all of the above operations were done in
a glove box' under nitrogen. The cleaned sodium
was transferred under nitrogen to a pre-weighed
tube equipped with a Suba-seal. The tube containing
sodium was weighed and then again was transferred
to the glove box for further use.
108
4.2.5. Cumyl Potassium
The cumyl potassium (Orgmet. Inc. Hampstead,
N.H., U.S.A.) was supplied as a suspension in n-heptane
in the presence of an excess of metallic potassium.
Cumyl potassium must be handled in a glove box since
it is very sensitive to air and moisture. 10m1 of
commercial K+- Cum was poured in a beaker containing
50cm3 pure THF. Then it was filtered through a
porosity 3 sintered glass funnel to leave behind
the metallic potassium. The solution of K+Cum in THF
was then stored in a suitable container - under
argon Figure (4-8).
• 4.2.6. Styrene
Styrene (B.D.H.) is stabilized by 0.001 to
0.002% w/w t-butyl catechol. It was washed three
times with 10% w/v aqueous solution of sodium
hydroxide and six times with distilled water. It
was kept for 10 minutes over anhydrous calcium
sulphate. Then gradually powdered calcium hydride
was added and the mixture was stirred overnight
before fractional distilation at low pressure.
The middle fraction was collected over some
fresh powdered calcium hydride in a flask. The
flask was then connected quickly to the vacuum
line through a splashhead and the mixture was
degassed. The mixture was stirred,with a magnetic
stirrer, over calcium hydride after again degassed
for about 1 hour. The styrene could then be
109
distilled to any other reaction vessel attached to
the vacuum line.
4.2.7. Ammonia
Ammonia (I.C.I. 99% w/w pure) was condensed
through the vacuum line from a cylinder into a flask
containing a small piece of cleaned sodium which was
immersed in liquid nitrogen. It was degassed twice
by placing the flask gradually and carefully in
methylated spirit. The temperature was controlled
so that the pressure of ammonia never exceeded
1 atm., and as a safety precaution tap (F) was left
open Figure (4-1). Purified ammonia could be
condensed from this flask into the reaction vessel
through the vacuum line.
4.2.8. Potassium Bromide
Finely ground Analar KBr was dried in a vacuum
oven for 24 hours and stored in a vacuum desicator
until required.
4.2.9. Acrylonitrile
Acrylonitrile (B.D.H. 99% w/w pure stabilized
with 0.005% w/w P-methoxyphenol) was purified by
successive washing with dilute sulphuric acid, (5% v/v),
dilute sodium carbonate (10% w/v) solution and
several times with distilled water. After drying
110
over anhydrous calcium chloride, it was then
filtered and stirred over powdered calcium hydride
for 24 hours. The monomer was fractionally distilled
at low pressure shortly before it was needed and the
middle fraction was collected in a flask containing
some fresh calcium hydride. Then the flask was
connected to the vacuum line and the acrylonitrile
was degassed.
4.2.10. Dimethyl Acetamide (DMA)
DMA (B.D.H. 99.5% w/w pure) was stirred
over calcium hydride for 24 hours before low
pressure fractional distillation. This distillation
was performed shortly before the DNA was used. The
middle fraction was collected in a two-necked flask,
one neck of which was equipped with a Suba-seal.
The flask was then connected to the vacuum line and
the DMA was degassed.
4.2.11. N-Methyl Pyrrolidone (NMP)
N-methyl pyrrolidone (B.D.H. 99.5% w/w
pure) was purified by stirring over excess molecular
sieve 4A for 24 hours followed by low pressure
distillation shortly before using. The middle
fraction was collected in a two-necked flask,
one neck of which was equipped with a Suba-seal.
The flask was rapidly connected to the vacuum
line and the NMP degassed.
111
4.2.12. Hydriodic Acid
Pure hydriodic acid (126-7°C b.p.) was
prepared by distilling Analar grade acid (B.D.H.)
over red phosphorus in an atmosphere of carbon
dioxide shortly before using. The presence of CO2
prevented the possibility of violent explosions
of mixtures of air and phosphorus hydrides in the
receiver. This purification procedure removed
sulphur compounds, phosphine and hypophosphorous
acid from the hydriodic acid.
4.2.13. Silver Nitrate Solution
SilVer nitrate (15g) was dissolved in 50cm
of water and then added to 400cm3 of absolute ethanol.
Several drops of concentrated nitric acid were added.
This solution was standardized against 0.05N ammonium
thiocyanate by the Volhard method.202
The solution
was very stable and the concentration remained
unaltered over several weeks.
4.2.14. Bromine Solution
A methanolic solution of bromine and potassium
bromide was used. Absolute methanol (500cm3) was
saturated with dry potassium bromide (about 10g) and
1.8cm3 of bromine was added. This solution was
stored in a dark bottle and kept in a dark cupboard.
It was standardized against sodium thiosulphate
immediately before using. The following solutions
were also prepared.
3
112
4.2.15. Potassium Iodide
10% w/w aqueous solution.
4.2.16. Sulphuric Acid
10% w/v aqueous solution.
4.2.17. Sodium thiosulphate
0.05 N standard solution.
4.2.18. Ammonium Thiocyanate
0.05 N standard solution.
4.2.19. Starch Indicator
1% w/v aqueous solution.
4.2.20. Ferric Ammonium Sulphate Indicator
Saturated aqueous solution (filtered).
4.2.21. Polyacrylamide
A finely powdered sample of commercial grade
of polyacrylamide (Allied Colloid Ltd.) which has
been prepared by a gel process using the KBr03/Na2S03
redox system was used. The sample had previously
been isolated by slurrying in methanol. The main
impurities present were water, methanol and traces
of initiator. For purification the commercial
sample was dried on a vacuum line using an IR lamp
113
for 5 hours, as previously described for nylon.
4.2.22. Nomex
A sample of pure powdered nomex (Du Pont)
was repurified by washing with distilled water in
aWaring blender three times, followed by filteration.
Finally, it was washed three times with methanol and
dried for 5 hours using an IR lamp on a vacuum line,
as previously described for nylon 66.
4.3. Synthesis
4.3.1. Tert-Butyl Hypochlorite204
(CH3)3COH+C1
2+NaOH ---÷ (CH
3)3COC1+ClNa+H
20
A solution of 80g (2 moles) of sodium hydroxide
in about 500cm3
of water was prepared ina 2 dm3 three-
necked round-bottomed flask equipped with a gas inlet
tubing reaching nearly to the bottom of the flask,
a gas outlet tube, a thermometer and a magnetic stirrer.
The flask was placed in a water bath at 15-20°C.
Since tert-butyl hypochlorite reacts violently with
rubber, PVC tubing was used for inlet and outlet
tubes. After the contents were cooled to this
temperature, 74g of tert-butylalcohol was added
together with enough water to form a homogeneous
solution. With constant stirring, chlorine was
passed into the mixture for about 1 hour. The upper
oily layer was then separated with the aid of a
separating funnel. It was washed with 50cm3 portions
of 10% w/w sodium carbonate solution until the
liquid attained a pH of about 5. It was finally
114
washed four times with an equal volume of water and
dried over anhydrous calcium chloride. The yield
was 78-107g tert-butyl hypochiorite. The product
was stored in a refrigerator inside a flask which
had been previously sealed off under vacuum. It
was strongly advised that the reaction vessel be
fitted with a thermometer which dipped into the
reaction mixture and that the flow - rate of
chlorine be regulated so that the temperature of
the reaction mixture never exceeded 20oC.
4.3.2. Aqueous Solution of Hvpochlorous Acid
To 150cm3 sodium hypochlorite (10-14% w/v
available chlorine) 40g MgSO4, 7H20 dissolved in
150cm3 distilled water was added. The flask,after
placing in a bath at 40-50°C, was connected to a
low pressure distilation apparatus. The acid was
distilled and collected in a flask immersed in a
methanol-"Cardice" mixture. The whole of the
apparatus was covered with aluminium foil to avoid
decomposition of the acid by light. The product
consisted of a solution of about 200cm3 HO C1 with
a concentration of about 0.2mol dm-3. The
concentration of HO C1 could be determined by
iodometric titration.
4.3.3. The o(- Form of Poly (meta7phenylene iso-phthalamide) (Nomex) 20b
A solution of 10.3g of isophthaloyl chloride
(98% w/w pure Aldrich Chemical Company Inc.) in 175cm3
115
THF containing one drop of concentrated sulphuric
acid was added to a rapidly stirred solution of
5.4g m-phenylene diamine (previously vacuum
sublimated) in 150cm3 water containing 10.6g
anhydrous Na2CO3
in a Waring blender at about 15°C.
The Waring blender was equipped with a specially
designed water bath for keeping the temperature low
and the motor was flushed with nitrogen-free oxygen
(to avoid explosion of THF) during the reaction.
After a reaction time of 5 minutes, the polymer
formed was collected on a sintered glass funnel
and was washed in the Waring blender three times
with water and twice with acetone. Thereafter, it
was dried at room temperature in a vacuum dessicator.
4.3.4. Preparation of N-Chloro Nylon 66183, 184
(a) With Tert-BuoC1
1.13g ground nylon 66 and 10cm31,1,2,2
tetrachloroethane were placed in a flask equipped
with a magnetic stirrer. 2.16g Tert-BuoC1 was
added to the flask and after 3 hours at 15°C, with
stirring, the mixture became homogeneous. The
chlorinated nylon was percipitated by addition of
100cm3 ether and was then filtered on a sintered
glass funnel. The product was purified by
dissolving in benzene at 50°C and percipitating
into ether. The polymer was dried in a vacuum
dessicator at room temperature.
116
(b) With HOC1 Solution
In a 500cm3 flask, 2.55g of nylon 66
particles of about 0.3mm diameter were covered with
220cm3
of 0.11mol dm-3
HOC1 solution and stirred in
the dark at room temperature. After 40 hours, the
product was filtered and washed several times with
. water. The polymer was purified as described in
4.3.4. (a).
4.3.5. N-Chloro Nomex
To a flask containing 2.38g Nomex and 30cm3
1,1,2,2 tetrachloroethane, 4,32g t-BuOC1 was added
and the mixture was stirred for 3 hours at room
temperature. The reaction was heterogeneous and
the polymer was filtered and purified by dissolving
in N-methyl pyrrolidone and precipitating into
ether. The product was dried in a vacuum oven at
room temperature. The reaction was also made
homogeneous when N-methyl pyrrolidone was used as
a solvent instead of tetrachloroethane.
4.3.6. Reaction of Living Poly(ethylene Oxide) and N-Methyl Pyrrolidone
(a) Preparation of Living Poly (ethylene-oxide)
The reaction vessel Figure (4-9) was
connected to the vacuum line through socket A.
The flask was evacuated and filled with high pure
argon for three times in order to create an inert
atmosphere. The pressure of argon was kept at
117
2cm Hg below the atmospheric pressure. 10cm3
cumyl potassium in THE solution with approximate
concentration 0.05mol dm-3
from the vessel
Figure (4-8) was introduced to the reaction vessel
Figure (4-9) by syringing through the Suba-seal
and high vacuum tap. The reaction vessel was
immersed in liquid nitrogen and evacuated.
40cm3 purified THE was distilled into reaction
vessel. Some ethylene oxide which was kept over
a sodium mirror was distilled into the calibrated
tube Figure (4-7). The calibrated tube was
immersed in an ice bath for measuring the volume
of EO at a constant temperature. Finally, 10cm3
of EO from the calibrated tube was distilled into
the reaction vessel. The flask was sealed off from
part B and stirred for 12 hours at room temperature.
(b) Introduction of N-Methyl Pyrrolidone to Living PEO
Argon was allowed to fill the space between
the Suba-seal and the break seal of the vessel
containing living PEO Figure (4-9) and, air was thus
displaced. Then the break seal was broken and argon
was introduced into the vessel. 5cm3 of pure N-
Methyl Purrolidone, previously stored under argon
in a two-necked flask connected to the vacuum line,
was transferred by means of a syringe through the
Suba-seal to the vessel containing living PEO. A
violet colour appeared, and after 5 hours stirring
under argon, 2cm3 ethanol was injected. There was
118
no colour change, but the colour finally disappeared
on injection of a few drops of dilute aqueous nitric
acid. The polymer was percipitated by pouring into
ether and after drying the IR spectrum of polymer
was recorded.
4.3.7. Metalation
Part I of the metalation vessel Figure (4-2),
a stopper, a sealed-off socket, a piece of sodium
in a beaker cover by a layer of paraffin, a pre-
weighed weighing bottle equipped with a tight
Suba-seal and the flasks containing cleaning solvents
(petroleum ether b.p. 80oC and petroleum ether b.p.
60oC) were placed in a glove box. Oxygen-free
nitrogen was passed through the glove box for 12
hours and then the cylinder was closed. A few
grams of P205
over a watch glass was then introduced
into the box to reduce the humidity of the atmosphere
and argon was then allowed to flow continuously
through the glove box. The argon (BOC highly
pure) was purified by passage through traps
containing concentrated H2SO4
and NaOH pellets,
respectively, before entering the glove box. Other
workers in the group have, however, shown that the
argon purification with H2SO4 and NaOH is unnecessary.
A suitable piece of freshly cut cleaned sodium was
transferred to the weighing bottle in the argon
atmosphere. The bottle was weighed quickly outside
the box and transferred again into the glove box.
Finally, the piece of sodium of known weight was
transferred from the weighing bottle into section
G of metalation vessel. The metalation vessel was
blocked by sealed-off socket and the stopper. 6g
119
purified ground nylon 66 was passed through a suitable
sieve and poured into section A Figure (4-2). Part
I was transferred from the glove box, connected to
the vacuum line through socket I and also joined to
Part II through the cone and socket D. The whole of
the reaction vessel (Parts I and II) were then
evacuated. A piece of cleaned sodium was dropped into
a 500cm3 flask, K, equipped with a magnetic follower,
which was connected to an adjacent cone on the vacuum
line. The rubber tubing between the ammonia cylinder
and the vacuum line was evacuated. The 500cm3
flask
K was immersed in liquid nitrogen and ammonia was
condensed from the cylinder into flask K while tap F
Figure (4-1) was open to control the pressure inside the
vacuum line. The ammonia was liquified by immersing the
flask in methylated spirit and finally it was degassed
using liquid nitrogen and the usual freeze-thaw cycle.
Sections A and E of the metalation vessel Figure (4-2)
were immersed in liquid nitrogen while tap H was closed.
Purified ammonia from the flask K was condensed into
section G using liquid nitrogen around sections E, F
and G. Then tap J was closed and the trapped ammonia
in section G was liquified by immersing section G
(also F and E) in methylated spirit while reaction
tube A was simultaneously cooled in liquid nitrogen.
Thus the liquid ammonia, under pressure, was forced
to section A dissolving some sodium on disc F during
this dissolving action. The process was repeated until
all traces of sodium on disc F had vanished. Thus when
120
section A was warmed and section E cooled with tap
H open and tap J closed, ammonia condensed from section
A to section G and dissolved some more sodium. Finally,
the vessel was sealed off at the capillary in section C.
After liquifying the contents of the tube, the tube was
rotated in an ice bath until the blue colour of sodium
in ammonia disappeared.
4.3.8. Preparation of Graft Copolymers of Nylon 66 and PEO rpoly(hexamethylene adipamide-g-ethylene oxide)]
As soon as the blue colour (4.3.7.) had
disappeared, the reaction vessel A was immersed in
liquid nitrogen. The previously sealed off capillary
at C was opened using a glass knife and hot glass
rod while the contents of the vessel were maintained
frozen. The vessel was connected quickly to the
vacuum line through socket B and the air was pumped
off. The whole of the ammonia in the reaction
vessel was then distilled into another empty 500cm3
flask through the vacuum line. During this distillation
the tap F Figure (4-1) was open. The 500cm3
flask
containing the ammonia was disconnected from the line
and left in a fume cupboard. In order to remove
traces of ammonia, the metalated nylon was left
under vacuum for 3 hours at room temperature. Then
75cm3 purified THE from a graduated vessel was
distilled into the reaction vessel A. Finally,
24cm3 purified ethylene oxide at 0
oC was distilled
121
from the graduated vessel Figure (4-7) into the
reaction vessel.A. Then the vessel A was sealed off
again using capillary below socket B. The tube was
rotated in a water bath at 60oC for 3 hours. The
polymer gradually became swollen during the grafting
reaction. The living polymer was terminated after
breaking the capillary at the top of the A by
adding a solution of 10cm3 THE containing 3cm
3
90% w/w formic acid.
4.3.9. Determination of Ethylene Oxide Volumetrically201
Trap B Figure (4-5) was filled with a
suspension of a small amount of red phosphorus
in enough water to cover the inlet tube. 10cm3
of silver nitrate solution was pipetted into
absorption tube C. 15cm3
of bromine solution in
methanol was pipetted into the spiral absorption tube
D. 10cm3
of 10% w/w KI solution was placed in the
last tube E. 0.1g of the nylon-g-PEO was placed
in the reaction flask A with a glass ball and 10cm3
of hydriodic acid, A mixture of lcm3 of slightly
warmed phenol and 2cm3 of propionic anhydride was
added to the reaction flask,in order to increase
the solubility of the graft sample in the acid.
The flask A was connected to the main apparatus
Figure (4-5) and a slow stream of carbon dioxide
from a cylinder was passed through, while the flask
was heated slowly in an oil bath until a temperature
122
of 140oC-145
oC had been reached. The flask was
maintained at about 140oC for approximately 1 hour.
Two indications of the completion of the decomposition
reaction were the absence of any cloudy reflux in
the condenser above the reaction flask A and the
nearly complete clarifications of the supernatant
liquid in the silver nitrate trap C. Five minutes
before the completion of the reaction the silver
nitrate trap was heated to 50°C-60°C with a hot air
blower to drive out any dissolved olefin.
At the completion of the decomposition, tubes
D and C were disconnected cautiously in that order.
The carbon dioxide source then was disconnected and
the oil bath removed from flask A. The spiral
absorption tube D was then connected by its lower
adaptor to a 500cm3 iodine titrationflask containing
10cm3 of 10% w/v aqueous KI solution and 150cm3
water. The potassium iodide tube E was removed and
the side arm from D was rinsed with water into tube
E. The bromine solution was allowed to run into the
titrationflask through the appropriate stopcocks
and the tube D and spiral were rinsed with water
which was added to the titration flask. The
contents of the potassium iodide tube E was added
to the titration flask, which was then stoppered
and allow to stand 5 minutes at room temperature.
5cm3
of 10% w/v sulphuric acid was added and the
solution was titrated at once with 0.05N sodium
thiosulphate using 2cm3
of starch indicator solution.
The contents of the silver nitrate trap were
rinsed into a separate flask, diluted to 150cm3 with
water, heated to boiling point, cooled to room
123
temperature and titrated at once with 0.05N ammonium
thiocyanate, using 3cm3 of ferric ammonium sulphate
solution as an indicator.
4.3.10. Viscosity
Limiting viscosity numbers of nylon 66,
regenerated nylon 66 and nylon-g-PEO were measured
in formic acid (90% w/w) at 25°C. A plot of
viscosity number and logarithmic viscosity number
against concentration for nylon 66 is shown in
Figure (4-11). The limiting viscosity number [1]
is given by ] = lim Isp = lim( In Y1 r)
C-40 C C-40
nsp specific viscosity 1r relative viscosity
C concentration
and [1] can be used for the calculation of a
viscosity average molecular weight M from:the
Mark-Houwink equation!
4 [1 ] = KM where M = My and K and o<
are values for fractionated samples.
In mixed solvents, the solutions were made
by dissolving a weighed amount of polymer directly
in the solvent mixture measured out volumetrically.
4.3.11. Determination of Molecular Weight of Nylon 66 and Regenerated Nylon 66
The molecular weight of purified nylon
66 (I.C.I.) was determined by the viscometric method
o i at 25C in formic acid (90% w/w). A sample of the
124 .
nylon was 30%(based on numbers)metalated and
regenerated as soon as the blue colour disappeared
by washing with a dilute aqueous solution of
nitric acid. Finally, it was washed several times
with distilled water followed by ethanol and dried
in a vacuum oven at 60oC for 24 hours. Then •
molecular weight of regenerated nylon 66 was
determined as described above.
4.3.12. Preparation of Nylon 66 Poly acrylonitrile Graft Copolymers [Poly(hexamethylene adipamide -q- acrylonitrile)]
A sample of nylon 66 (4.42g) was metalated
30% (based on numbers) as described previously. The
sealed off capillary was broken and the additional
part Figure (4-4) was joined to the vessel A by means
of the cone and socket and quickly connected to the
vacuum line. Ammonia was condensed from the reaction
vessel to another flask as was done for grafting
ethylene oxide to nylon. The metalated nylon was
left under vacuum for 3 hours at room temperature.
The air which was trapped between the Suba-seal and
vacuum tap Figure (4-4) was pushed out by injection
of argon. The pressure of the reaction vessel and
the vacuum line was kept at 2cm Hg less than
atmospheric pressure by introducing argon to the
line. 80cm3
of purified DMF, which was kept under
argon, was injected into the reaction vessel by a
syringe. Finally, the line was evacuated and the
125
necessary amount of purified acrylonitrile was
distilled into the reaction vessel through the
vacuum line. The vessel was sealed off as
described previously. The reaction of acrylonitrile
with metalated nylon 66 was found to be very fast,
so the contents of the tube were liquified while
keeping the temperature as low as possible. Finally,
the tube was shaken for 11/2 hours in a horizontal
position while immersed in a mixture of Card-ice
and methanol. The living polymer had a pale
yellow colour and the particles floated and were
swollen in DMF. The living polymer was terminated
by a 3% solution v/v of conc. H2SO4 in DMF which was
added until the pH of the liquid phase was 7. The
mixture was poured into a beaker containing distilled
water, and washed several times with distilled
water. Finally, it was dried for 24 hours in a
vacuum oven at 60oC.
4.3.13. Fractionation of Nylon 66 Poly acrylonitrile Graft Copolymer
A sample of the graft (30% metalated,
containing 64.5% w/w acrylonitrile) was mixed with
DMF and stirred at about 35oC. The liquid phase
was separated from the solid one by centrifuging
and filtration. The solid phase was washed with
DMF. The polymer was separated from the liquid
phase by pouring the solution into a 2% w/w aqueous
solution of Na2SO4. The fraction which was
126
insoluble in DMF was dried in a vacuum oven at 60oC.
This fraction was almost soluble in HCOOH (90% w/w)
but the insoluble particles were highly swollen and
thus in a jelly form. The fraction soluble in DMF
was split into three fractions by adding HCOOH as
non solvent. The IR spectrum of each fraction was
obtained by casting a film from DMF solution. The
colour of the DMF soluble fraction rapidly turned
yellow when dissolved in the solvent (DMF).
4.3.14. Anionic Polymerization of Acrylonitrile207
A 250cm3, three necked, round-bottomed flask
was fitted with a stirrer, an inlet tube for the
introduction of oxygen free-nitrogen and an outlet
tube. The nitrogen was dried by passing it through
silica gel and the equipment was flamed out under
nitrogen immediately prior to use. In the flask
was placed 60cm3
of freshly distilled DMF and 10cm3
of purified acrylonitrile. The flask, with its
contents, was immersed in a cooling bath consisting
of Card-ice and alcohol and the final temperature
was about -50oC. The initiator, 2cm
3 of a saturated
solution of anhydrous sodium cyanide in dry DMF
was rapidly introduced by means of a syringe. Sodium
cyanide was dried by storing in a vacuum desicator
over silica gel for several days prior to use. A
saturated solution of this salt in DMF contains less
than lg of cyanide in 100g of DMF. Within a few
seconds of adding the initiator, the temperature of
the reaction mixture increased and the solution
became viscous. The contents of the flask were
stirred for about 30 minutes in the cooling bath.
127
Then 5cm3 of T% v/v concentrated sulphuric acid in
DMF was added to terminate the polymer and to adjust
the acidity of the mixture to a pH of 7 or less.
The polymer was isolated by precipitation in water
and was dried in a vacuum oven at 60oC. The yield
was quantitative.
4.3.15. Unsuccessful Attempt to Prepare Graft Copolymer of Nylon 66 Styrene
The procedure which was followed for preparation
of this graft copolymer was similar to the preparation
of graft copolymer of nylon 66 poly(ethylene-oxide).
Instead of ethylene oxide, purified styrene was
distilled into the reaction vessel and THF was used
as solvent. The temperature of the reaction was
raised to 75oC and rotation continued for 8 hours.
There was no indication of grafting (colour-IR
spectroscopy).
4.3.16. Preparation of Sodium Naphthalene.
A two necked flask was flamed and under
nitrogen. Then the flask was equipped with a Suba-
seal and a magnetic stirred. It was connected to
the vacuum line and evacuated. Under argon 15g
of sublimated naphthalene and about 1.5g sodium
were added to the flask. The flask was evacuated
and 50cm3
of THF, which had been kept over Na/K
alloy was distilled into the flask. The reaction
128
started almost at once, as evidenced by the appearance
of the dark green colour of sodium naphthalene.
The exothermic reaction proceeded rapidly and after
2 hours of stirring, the reaction was considered to
be complete. A 3cm3 aliquot was withdrawn at this
point and quenched in methanol. The concentration
of NaNp was determined with standard hydrochloric
acid.
4.3. 17. Metalation of Nomex with Na/NH3
A sample of Nomex was placed in the reaction
vessel which had been used previously for the metalation
of nylon 66. The procedure followed was similar to
that for the metalation of nylon 66. Nomex could
be metalated up to 90% (based on numbers) and the
reaction time was only about 2 hours. The end of
reaction was determined by the disappearance of the
colour of the Na/NH3 solution. The metalated Nomex
had a red colour.
Metalation of Nomex with Sodium Naphthalene
A known amount of Nomex was placed in a reaction
vessel equipped with a magnetic stirred Figure (4-10).
The necessary amount of sodium naphthalene in THE
was injected under argon to the reaction vessel
through neck A. Finally the reaction vessel was
sealed off through necks A and B. The basis of the
calculation for 100% metalation of Nomex (based on
numbers) is:
+ _ 0
N Na N_
O c-N- -c-
129
0
0
C -NH -
2Na -C-
2 x 23g sodium metalation> 238g Nomex
A sample of Nomex was metalated easily to
11% with sodium naphthalene at room temperature.
The end of reaction was determined by the disappearance
of the greenish-blue colour of the sodium naphthalene
and the appearance' of the red colour of metalated
Nomex. An attempt was made to metalate a sample of
Nomex to 30% (based on numbers) using sodium
naphthalene at room temperature. After two days the
greenish-blue colour had not disappeared. Then
reaction was tried at 50°C and the greenish blue
colour disappeared. The reaction vessel could be
connected to the vacuum line through the socket C
for further experiments.
4.3.19. Unsuccessful Attempt to Prepare Graft Copolymer of Nomex Poly (ethylene-oxide)
A sample of Nomex was metalated 30% (based
on numbers) with Na/NH3. The procedure followed
for grafting Nomex ethylene oxide was quite similar
to grafting nylon 66 with ethylene oxide. THE was
used as solvent and the mixture was rotated in a
bath at 60°C for 8 hours. There was no evidence of
130
grafting. Finally, the reaction was performed at
80oC for 4 hours, but again there was no change in
the colour. The polymer was terminated by a dilute
aqueous solution of nitric acid and the IR spectrum
was obtained. The spectrum indicated that no
grafting had occurred.
4.3.20. Preparation of Nomex Poly acrylonitrile Graft Copolymers Poly (meta-phenylene iso-phthalamide-q-acrylonitrile)
A sample of Nomex (3.2g) was metalated 90%
(based on numbers) with Na/NH3. The procedure followed
for preparation of this graft copolymer was quite
similar to the preparation of the graft copolymer
of nylon 66 poly acrylonitrile. 80cm3
purified DMF
was used as solvent and 6cm3
purified acrylonitrile
was distilled in the vessel. The contents of the
vessel were warmed cautiously until they liquified
but the temperature was maintained as low as possible.
The reaction vessel was shaken in a bath of methanol
Card-ice for 2 hours. The solution became viscous
and the particles became swollen. Finally, the
polymer was terminated by a solution of DMF which
contained 3cm3 concentrated sulphuric acid. The
mixture was poured into water and the polymer after
filtration and washing several times with distilled
water, was dried in a vacuum oven at 60°C for 24
hours. The percentage of grafting w/w was checked
both by measuring the increase in weight and also by
nitrogen microanalysis. Again the grafting reaction
was heterogeneous.
131
4.3.21. Proof of the Absence of the Homopolymer, Polyacrylonitrile, in the Preparation of Nomex - Poly(acrylonitrile) Graft Copolymer
A sample of the graft containing 60% w/w PAN
(metalation 90% based on numbers) was split into two
fractions, soluble (X) and insoluble (Y) in DMF. A
solution of 1.5% w/w of the soluble fraction (X) in
DMF was prepared. Methanol was chosen as non solvent
and the standard method for fractional precipitation
was used at 30oC. The polymer (X) was thus split
into eight fractions of approximately equal weights.
The IR spectrum of each fraction was obtained by
casting a film on a sodium chloride disc and drying
for 24 hours in a vacuum oven at 60oC. Three small
samples from each of the eight fractions were sent
for nitrogen microanalysis and a sample of (Y) was
also microanalysed.
4.3.22. Preparation of N-Derivative of Nomex (N-Benzyl Nomex)
A sample of Nomex (7.450g) was metalated
75% (based on numbers) by Na/NH3. The further
experimental procedure was similar to that involved
in the preparation of the graft copolymer of Nomex
polyacrylonitrile. 100cm3 purified DMF was
injected into the reaction vessel through the
Suba-seal and the vacuum tap, all apparatus being
under argon. Finally, an excess of benzyl bromide
was injected into the reaction vessel and the
vessel was sealed off after degassing. The reaction
tube was warmed up to 35oC and the red colour
132
gradually disappeared while Nomex particles acquired
a jelly-like appearance. After shaking the vessel
for about 11/2 hours, there was no evidence of any
remaining red colour. The viscous solution was
poured into distilled water and filtered. The
polymer was wahsed several times with methanol
and dried in a vacuum oven at 65oC for 30 hours.
The IR spectrum was obtained by casting a film
from a viscous solution in DMF on a sodium
chloride disc and drying in a vacuum oven at
60oC for 24 hours. A sample was sent for nitrogen
microanalysed.
4.3.23. An Unsuccessful Attempt at the Metalation of Polyacrylamide
An attempt was made to metalate polyacryla-
mide on to extent of 30% (based on numbers) with
Na/NH3. However, even after stirring for two days
at room temperature, there was no decrease in the
intensity of the blue colour of Na/NH3. It was
assumed that the attempted metalation had been
unsuccessful.
Figure (4-1) - The Vacuum Line
134
vtzaztvm L
H e
A
1•
Figure(4-2) - Metalation Vessel
Figure (L-3) - Pyrex glass disc
Figure (,4-- .4)
/35
0
10
20
30
40
50
60
Figure ( 4-5- )
•
•
4."
I
nitrogen or air
•
111. ISO
•••
••• •
•
Gas Filter
•
• •
•
•
••■
•
• •
Nitrogen •
•
•
•
•
• •
•
.
136
Figure (4-6) - Viscosity Pumping Device
137
Figure (4-7) Figure (4-8)
Figure(4 -9) Figure(4-10)
1.6
t2
0.8
0.4
c/legcm-3
Figure(4-11) - Viscosity Number and Logarithmic Visocisty Number against Concentration of Nylon 66
138
5. RESULT AND DISCUSSION
5.1. Nomex, N-chloro Nylons and N-Methyl Pyrrolidon as solvent
5.1.1. Nomex.. The preparation and characterization of aromatic
nylons have been investigated by several authors.208,215
In this work, Nomex was prepared by miscible interfacial
polycondensation. The rate of polymerization in an
interfacial system decreases rapidly as soon as the
polymer precipitates. A polar solvent, miscible with
water, is employed to dissolve the diacid chloride and
water is with added polar organic solvent, the solvent
for the aromatic diamine, when necessary. The polar
solvent will increase the rate of polymerization and
also increases the solubility of the polymer. The use
of the miscible interfacial technique216
yields high
molecular weight aromatic polyamide under suitable
experimental conditions.
Textile fibres from synthetic polymers are
conventionally prepared by extrusion of a melt or a
solution of the polymer. Thus relatively low melting
point polymers or polymers of high solubility are from
an economic point of view, most favourable for fibre
formation. However, the low melting point and high
solubility of a textile material are highly undesirable.
Nomex is capable of existing in two structural forms.
139
One form is called "alpha" ( c4) having high solubility
and the other is called "beta" (/3) possessing low
solubility. In both the of form and the A form, the
polymer may exist in the amorphous or the crystalline
state. The oc form is soluble in solvents such as DMF
and DMA, N-methyl pyrrolidone, whether in the amorphous
or the crystalline state. The form is insoluble in
such solvents whether in the amorphous or crystalline
state. Sweey 206believes that a network of interchain
hydrogen bonding, which may be ordered enough to be
crystalline, between the carbonyl oxygen and weakly
acidic -NH groups of adjacent chains is characteristic
of the beta form Figure (5-2). The o< form of the polymer
is largely free of such interchain bonding but there
exist ihterachain hydrogen bonding between carbonyl oxygen
and weakly acidic -NH groups of another recurring unit in
the same chain Figure (5-1). The of form can be converted
to the /3 form by:-
(a) increasing the chain mobility with heat,
suitable plasticizers or solvents, so that
the chains can rearrange to the more
thermodynamically stable /3 structure;
(b) by ordering the chain molecules by some
process of orientation. The Cie form in
solution is converted to the /3 form slowly
at room temperature but more rapidly at
higher temperature. Thus the Xform of
the polymer must be prepared by a low
temperature technique.
0 0 11 11
-C -N-R-N-C -R
H H C=° O 0 H-N
0 H 0 11 1 11
-N-C-R-C-N-R-N-C-
1 11
H 0 O H 0
140
u u Ii I II
-N-R-N-C-R-C-N-R -N-C-R-C-N-R-N-C-R-
1 1 1 I u I
H H H H 0 H
Figure (5-1) (X Form
Figure (5-2) /3 Form
5.1.2. N-Chloro Nylon 66 and N-Chloro Nomex
All N-chloro nylon 66 samples were in the form
of a white powder regardless of the degree of chlorination.
The extent of N-chlorination increased the solubility in
benzene, 1,1,2,2 tetrachloroethane and chloroform. N-
chloro polyamides can oxidize potassium iodide easily.217
Thus N-chloroamide groups may be determined quantitively
by treating the polymer with a KI solution and then by
titration of the librated iodine. A sample of highly
chlorinated nylon 66 after purification was microanalysed
for chlorine and showed that 96% of the original -NH- has
been converted to -NC1-. The IR spectrum of N-chloro nylon
66 was obtained by casting a film onto a NaC1 plate. The
spectrum showed the -NH band was missing at 3300cm-1
and the amide band II at 1530cm1
was also absent Figure (5-3).
Occasionally N-chloro nylon 66, prepared using t-BuOC1 was
not soluble in benzene. This might be due to the high
reactivity of the N-chloro nylon 66 which could crosslink
in the homogeneous reaction system. When HOC1 was used
141
as the chlorinating agent, the reaction was heterogeneous.
The product was readily soluble in benzene and the former
insolubility problem was not observed.
The c< form of Nomex is not soluble in DMF or DMA
at room temperature, since it is continuously converted
to the /3 form of the polymer. A highly chlorinated
sample of Nomex starting from the oC or /3 forms was
soluble in DMF and DMA at room temperature. The increased
solubility of the N-chloro Nomex samples is presumably due
to the destruction of H-bonding. Microanalysis of highly
chloronated Nomex:
A: The sample which was prepared heterogeneously
C = 53.86% H = 2.92% N = 8.72% Cl = 21.18%
B: The sample which was prepared homogeneously
C = 53.60% H = 2.98% N = 8.51% Cl = 23.00%
Theoretically if Nomex was chlorinated 100% the
results should be:
C = 54.72% H = 2.60% N = 9.12% Cl = 23.12%
The N-chloro polyamides were prepared as potential
intermediates for the preparation of graft copolymers, but
their use was unsuccessful.
142
A
lo.
go
So
40
Lb
4N• 760° loco, 2Coo 2000
16 0° loon 62-5
B
Figure (5-3)
A - IR Spectrum of N-Chloro Nylon 66 cast a film from Benzene
B - IR Spectrum of Nylon 66 cast a film from HCOOH
e 7
143
5.1.3. Use of N-methyl pyrrolidone as solvent in the preparation of Nomex graft copolymers
N-methyl pyrrolidone, NMP, has been successfully 218,219
used as a solvent for a wide variety of ionic reactions,
involving attack by nucleophilic groups, such as EN.
The high solubility of Nomex in NMP prompted the
use of NMP as a solvent in the preparation of Nomex graft
copolymers. Preliminary experiments were therefore carried
out to check the possibility of a direct reaction between
living PEO and NMP, but a violet colour was produced
(4.3.6 (b)), indicating a direct reaction had occurred.
The polymeric product, after isolation, was shown to be
dead PEO by IR spectroscopy.
The most likely reaction scheme would appear to
be:
Me
C6 H5
-C-(CH2 -CH
2 0) n -CH
2 -CH
2 OK Me
Me
C6 H5
-C-(CH2-CH
20)
n-CH
2-CH
2OH
Me
CH3
-K+
0 (violet)
CH3
(5-1)
EHK-F
L 0 Nr
CH3
H+ NO3 > ( + K+No3
(5-2)
-
Termination N/-
CH3
144
which indicates that there is initial nucleophilic attack
on the -CH2- group adjacent to the %F=0 in NMP by ^~^CH2-CH25,
with termination of the polymeric anion. This is consistent
with the result of Gassman et a1220
using NMP.
L L■ N
= 0 + 2NaNH2 + 2MeI -- -> — 2NaI +
(excess) N
CH3 CH3
0
+ 2NH3
Me
(5-3)
which again suggests initial nucleophilic attack by NH2 on
the -CH2- group adjacent to the ;C=0 in NMP.
Me
The result showed that NMP was not likely to be a
suitable solvent for ionic grafting reactions due to its
high termination potential.
145 4
5.2. Graft Copolymers of Nylons
5.2.1. Introduction
The preparation of graft copolymers of nylon has
been attempted by several authors. Most of the work, so
far, has been based on different radical techniques.
Initial attach in most cases takes place at the methylene
group attached to nitrogen to give a free radical.
Alkoxyalkylated nylon 66221
has been made by acidic
catalyzed addition of formaldehyde to nylon 66 in the
presence of alcohol.
-NHCO- + CH2O + ROH -N-CO + H2O ( CH
2OR
(5-4)
(alkoxyalkylated nylon)
Reaction of nylon with ethylene oxide lead to a
product with poly(ethylene oxide) side chains attached to
the amide nitrogen atom. However, in all of these reactions,
the number of monomer units per branch is unknown and the
exact number of branches cannot be predicted.
In an ideal ionic polymerization, initiation must
be rapid compared to propagation, so that all the growing:
chains become available at approximately the same time.
Each polymer chain will have an equal chance to add monomer
and all of the chains should have an equal size. So, ionic
polymerization techniques offer the possibility of preparing
graft copolymers with an exactly known number of branches and
a defined number of monomer units per branch.
146
However, according to the literature, there has
been little attention paid to the preparation of graft
copolymensof nylors ionically. The reason may be due to
the problem of finding a suitable solvent for the metalation
of nylons.
It is well known that the anion of acetamide
reacts as a strong nucleophilic reagent.
CH3CONHK
+ + C
2H5Br > CH
3CONHC
2H5 + KBr (5-5)
This reaction prompted some of the work reported
in this thesis whereby nylons were modified by ionic
reactions.
The preparation and characterisation of Nylon 66
and Nomex graft copolymers will be discussed in the first
part of this chapter. The influence of the heterogeneity
of the reaction system on the graft length distribution and
on the properties of the graft copolymers will be discussed
in the second part of this chapter.
5.2.2. Metalated Nylon 66
Metalated Nylon 66 is a white compound and is
widely dispersed in liquid ammonia on shaking. The end
of the metalation reaction was denoted by the disappearance
of the blue colour of Na/NH3. The following relation was
used for the calculation of the percentage of metalation:
9 9I 4 [-C-(CH
2)4-C-N-(CH
2)6N-J
-4 2Na 100% metalation (based on numbers)
(5-6)
1 repeat unit (2/6g) nylon - 2 moles sodium
(2 x 23g) -4 100% metalation (based on numbers)
147
The percentage of metalation was determined by
the amount of sodium and nylon which were used. The time
of metalation reaction depended on different factors such
as reactant concentrations and the porosity of the nylon
particles. In Table (5-1) very approximate times of
metalation are given
No. of Sample % metalation (based on numbers)
ApprOximate time of metalation (hour)
I 10.0 xi
II 22.0 11/2
III 28.0 2
IV 40.4 211
V 56.7 7
[about 4g nylon used, reaction temperature 0oC,
NH3
80-100cm3 at room temperature, under pressure
amount of Na used = 4 x 46 x % metalation g 216 100
Table (5-1) metalation time for complete consumption of
sodium.
The metalation is a heterogeneous reaction and the
following scheme can be considered for the structure of the
anion 141
148
0 H Na/NH3 II
-C-N-
0 u _
[-C-N-]Na (5-7)
A sample of 30% metalated nylon 66 was regenerated
by washing with 20cm3
distilled water containing 2cm3
nitric acid. An IR spectrum was obtained by casting a
film from HCOOH on a NaC1 disc and this was compared
with the spectrum of the origin nylon. There was no
change in the IR spectrum, however.
0 0 H
[-C-N1Na+ + H2O -C-N- + NaOH (5-8)
5.2.3. Degradation of Nylon 66 in the Metalation Reaction
Miller et a1222
reported that proteins were
partially ammonolyzed by ammono bases and ammono acids
in liquid ammonia. The extent of ammonolysis depends
upon the nature of the base and the temperature. There
was evidence that ammonolysis by potassium amide proceeds
more rapidly than sodamide at about 40°C. They found
ammonolysis of a peptide link would give a free amino
group and a free amide group.
In order to limit the ammonolysis of nylon 66,
ammonia was distilled off from the reaction vessel as
soon as the blue colour disappeared and the reaction was
performed at 0°C. The limiting viscosity number of a
sample of the original nylon 66 was measured in formic
acid at 30°C and compared to limiting viscosity number
of a regenerated sample after 30% metalation. The
results are:
149
[Y) 140.0cm3g- 1 at 30°C for nylon 66
[I] = 138.5cm3g-1 at 30°C for regenerated nylon 66
Taylor223
reported the following equation for
the relation between limiting viscosity number and the
molecular weight of nylon 66:
[ 11 = 0.11 x Mn 0.72 cm3g_1
SO
Mn = 20500
For origin nylon 66
Mn = 20200
For regenerated nylon 66
It was concluded that degradation of the nylon
66 after 30% metalation (based on numbers), distilling
ammonia from the reaction vessel as soon as the blue
colour disappeared, was negligible. The following equation
-could be suggested for ammonolysis of nylon:
0 0 Na Na0 0 H H n n _ n n
[-C-(CH2)4-C-N-(CH
2)6-R-C(CH
2)4-C-N-(CH
2)6-N-] + NH3
0 0 11 II
[-C-(CH2)4-C-N-(CH
2 )6 N-1Na
+ + H
2 NC(CH
2 )4 C-
1 , „ " Na H 0 0
(5-9)
The solution of nylon in formic acid was shaken
for 12 hours before viscosity measurements, in order to
obtain a true solution, since otherwise jelly-like
particles were formed in the solution.
5.2.4. The Grafting of Nylon 66 with Poly(ethylene-oxide)
5.2.4.1. Extraction of Homopolymer and IR Spectra
Nylon 66-g-PEO was insoluble in THF. The
homopolymer of ethylene oxide was separated from the
Percentage of ethylene oxide grafted (grafting
weight increase due to grafting (q)
°A) weight of the graft
150
graft copolymer by extraction three times with THF. The
product, after precipitation and centrifuging was a
viscous liquid of about lcm3 volume. In this system there
was no formation of PEO with a molecular weight of> 440.
The small amount of by-product might be PEO formed by
initiation by traces of residual ammonia. To limit the
traces of the homopolymer PEO, mixed with the graft
copolymer, a sample of the purified graft copolymer after
the extraction with THF was dissolved in HCOOH and
precipitated by water. IR spectra of nylon 66 and the graft
copolymer was obtained by casting films from HCOOH on NaCl
discs and drying in a vacuum oven at 60oC Figure (5-4). The
graft copolymer showed a strong absorption band at about
1100cm1 which confirmed the presence of aliphatic ether
linkages. The intensity of this band was in proportion
to the amount of ethylene oxide in the graft.
Values of the percentage of grafting w/w used in
this work were defined by the following relation:
x 100
copolymer (g)
(5-10)
The percentages of grafting were determined by
three main methods involving the increase of weight,
nitrogen microanalysis and use of a volumetric technique.
cces ;Otte 269. 4toe
toe.
t5o.' j 12 10S• I I ; i 26 I g
—1 611%
0.0•
Se
41..
0-
151
(5-4)(A)- The IR Spectrum of Ny1:-.)n.66-g-PEO (PEO 28% w/w matalation 30%) cast a film from HCOOH
k I POI 15°0
1110. ; 625 0, ; Vfor
C,177
`figure (5-4)(B) - The IR Spectrum of Nylon 66-g-PEO (PEO 57% w/w metalation 30%) cast a film from HCOOH
Jiro
152
5.2.4.2. Determination of Ethylene Oxide Quantitatively by the Morgan Titration Method 201
When an ethylene glycol ether or polymeric ether
is decomposed by boiling hydriodic acid, a complex series
of substitution and degradation reaction occurs leading
to the formation of alkyl iodides and olefins. The
following equation summarizes the different reactions
which occur for the mono ether:
ROCH2CH2OH + (3 + x)HI RI+(x)CH
3 CH2 I +
(1-x)CH2 = CH
2 + I
2 + H2O
(5-11)
where x is a variable number less than 1. The ratio of
ethyle iodide and ethylene obtained varies with reaction
conditions. The standard bromine solution reacts with both
the alkyl iodide and olefin produced from glycol derivatives
but not in an equivalent manner:
RI + Br2
RBr + IBr
IBr + 3H20 + 2Br
2 HI0
3 + 5HBr
CH2 = CH
2 + Br
2 CH2BrCH
2Br
The final single trap in the apparatus (4.3.9.)
containing potassium iodide solution was added to the system
to collect any bromine swept out by the flow of carbon
dioxide.
153
After the titration of the bromine and the silver
nitrate traps the results were substracted from the
corresponding blank titration. The following calculation
holds for ethylene oxide:
Difference in cm3 of Na2S203
x N x 2.203 = %C
2H40(as C
2H4)
Weight of sample (g)
Difference in cm3 of NH4SCN x N x 4.405
= %C2H40(as C
2. H5 I)
Weight of sample (g)
where N is the normality of the Na2S203 solution.
The total percentage of C2H40 as C2H4 and C2H5I
represents grafting percentage as defined in equation (5-10).
Cohen et al181
synthesized a low molecular weight
analogue of N-hydroxy ethyl nylon:
0
CH3 CH2 N-C-CH
2-CH
3 CH 2
CH2
OH
The compound was analysed by the Morgan method and a
satisfactory null value was reported. The nitrogen carbon
bond and the combined ethylene oxide group attached directly
to the nitrogen of the nylon backbone were not destroyed.
Therefore only that portion of the combined ethylene oxide
154
of hydroxyethyl nylon which is enclosed in parentheses
in the following equation was determined:
NH NCH -CH 0(CHCH0)H + (n+1)C2H40 --a• 2 2 2 2 n
C=0 C=0 1 1
(5-15) • HI
N-CH2 -CH
2 I
C=0 + xC2H4
+ (n-x)C2H5I
5.2.4.3. Relation of Metalation and Grafting
Five samples of Nylon 66 (each four grams) was
metalated with different percentages of metalation. To
each sample was added 15cm3 ethylene oxide in 0
oC, 50cm
3
THE and the reaction time was 3 hours at 60oC. So the
reaction conditions were identical and only the
percentages of metalation were different. The percentage
of grafting for each sample was measured, after
purification by increase in weight, nitrogen microanalysis
and titration. The results are shown in Table (5-2).
In Figure (5-5) the percentage of metalation is plotted
against the percentage of grafting. There in a linear
relation between the percentage of metalation and
grafting up to about 30% metalation. Afterwards there
was curkbre which was thought to be due to the
heterogeneity of the system. This will be discussed in
a later section.
155
To a sample of nylon 66 4g, 15cm3 ethylene oxide
(at 0°C) and 50cm3 THE was added. After rotating the tube
at 60oC for 6 hours (as was done for nylon 66-g-PEO), the
IR spectrum and nitrogbn microanalysis showed'that no
reaction occurred between the ethylene oxide and the nylon
in the absence of metalation.
In order to optimize the grafting efficiency while
minimizing degradation, 30% metalated nylon 66 was chosen
for further studies.
TABLE (5-2) - Relation of % Metalation and % Grafting
Metalation % (based on numbers)
N % w/w Grafting by N microanalysis % w/w
Grafting by titration % w/w
Grafting by increasing weight % w/w
Grafting average w/w
56.70 5.26 52.00 47.00 43.00 47.30
40.40 5.80 47.50. 46.00 44.00 45.80
27.90 5.13 53.70 41.00 40.00 44.90
22.30 7.30 37.70 39.00 30.00 35.60
10.60 9.90 27.80 22.010 18.00 22.60
(Nylon 66 4g THE 50cm3 E0 15cm3 at 0°C. Reaction time 3 hours at 60°C. 4 % metalation 16 Amount of Na - x 46 x 100
%
157
5.2.4.4. Solubility
The graft copolymer of nylon 66 poly(ethylene oxide)
was partially soluble in methanol. The graft copolymer was
split into three factions:
(I) Soluble fraction in cold methanol (at
room temperature)
(II) Soluble fraction in hot methanol (at
about 45°C)
(III) Insoluble in methanol but soluble in
nylon solvents such as formic acid.
A solution of the graft copolymer in methanol was
precipitated by the addition of diethyl ether.
A sample of graft copolymer containing 57% w/w PEO
(3a% metalation) was split into two fractions, one soluble
in methanol and the other insoluble in methanol. The
fractions were microanalyzed and the following results were
obtained:
Insoluble Fraction Soluble Fraction
C 61.42% 52.13%
H 10.02% 8.81%
N 10.98% 3.89%
The insoluble fraction contained 25.0% w/w PEO,
while the soluble fraction contained 70.8% w/w PEO. The
IR spectrum of each fraction was obtained by casting a
158
film on a NaC1 disc and both of the spectra showed -NH and
etheric absorption. Thus both fractions contained PEO.
Four samples of the graft copolymer(4g nylon,
15cm3 EO at 0°C, 50cm
3 THE and reaction times 3 hours at
60°C) were prepared for which the only difference was the
percentage of metalation. Each sample was split into two
fractions, one soluble in methanol and the other insoluble
in methanol. The relationship between the percentage of
solubility and metalation was studied. The -results are
shown in Table (5-3) and plotted in Figures (5-6,7). In
order to avoid degradation of nylon 66, metalation was not
carried greater than 40%. There was a linear relation
between increasing metalation and solubility in methanol
up to 30% metalation. Afterwards curvature occurred which
was thought to be due to the heterogeneity of the reaction.
Sample No. % Metalation % Polymer
% Polymer soluble in
insoluble in Me0H w/w Me0H w/w
I 10.0 26.2 73.7
II 22.0 46.3 53.6
III 28.0 67.1 32.9
IV 40.4 74.9 25.1
TABLE (5-3) Relation of Metalation and Solubility for Nylon 66-q-PEO
[Nylon 66 4g THE 50cm3
EO 15cm3 at 0°C. Reaction time
3 hours at 60°C] Na -4- x 46 x % metalation 216 100
lo go % metalation 3° 40 ro eo I0 .10
159
6o
4J 4-1 rt
4
›ifQ
"4 'X*
r-I 0 40
co.
40,
2.o .
I o
o LD 30 4o co ifo
% metalation 10 20 7' 4o c o
% metalation
Figure (5-5) - relation of % metalation and _ % grafting for Nylon 66-g-PEO
Figure (5-6) - relation of Figure (5-7) - relation of % metalation and % % metalation and % insolubility solubility in Me0H for in Me0H for Nylon 66-g-PEO Nylon 66-g-PEO
160
5.2.4.5. Phase Separation of Homopolymers and the Glass Transition of Copolymers
A - phase Separation: Mixing in a binary system
will occur when the Gibbs free energy,AG, is negative,
as defined by:
AG = AH - T. AS (5-16)
where AH and AS are the heat and entropy of mixing
respectively, and T is the absolute temperature. The
heat of mixing for a pair of homopolymers is generally
endothermic.
The interaction between chemically different
homopolymers, A and B, is characterised by an interaction
parameter, XAB, which takes higher values as A and B
become more incompatible. In the solid state, phase
separation occurs when )(AB reaches, a critical value,
()CAB) cr224
, where
(AB)cr = 1.1[(1--)1/2 + (-1' )1/2]2 andAG = 0 (5-17) nA nB
nA and nB are the degrees of polymerisation of the
homopolymers A and B. ).AB depends on the heat of mixing
of the two homopolymers (M). When a mixture is composed
of two non-polar homopolymers, the heat of mixing can be
predicted from:225
= V.(6A-6.B)2 .vA.vB (5-18)
where V is the molar volume of the system and vA and vB
are volume fractions. SA and B are solubility parameters
for homopolymers A and B. The solubility parameter is
related to cohesive energy density. Equation (5-18) is most
reliable for non-polar systems. Two dissimilar homopolymers
161
are therefore incompatible except for several rare
exceptions in which compatibility is due to favourable
interaction between polar groups:
B - Glass Transition of Copolymers: Gordon
and Taylor226
derived the equation:
W2 = (Tg -Tg1)/1K(Tg2-Tg) +
K = (2nr-24G)/(29R-18G) _ (5-19) -
for predicting Tg of a random copolymer in terms of
copolymer composition from the glass transition of the
homopolymers. In this equation Tgi and Tg2 are glass
transitions of component 1 and 2 and W2
is the weight
fraction of component 2. IS is the difference between
the thermal expansion coefficicnts of a homopolymer above
and below the transition temperature. Equation (5-19)
is adequate for most random copolymers. A single glass
transition was found when blocks are long for ABA
poly(styrene-b-methyl styrene).227
Bohn228
suggested that the best evidence for a
two phase system is when the melting points of crystalline
components, or the glass transition temperatures of
individual components, in a polymer mixture were observed.
Tg of a sample of the graft copolymer containing
28% w/w PEO (30% metalation) was measured Figure (5-8) and
compared with the homopolymers Nylon 66 and PEO Table (5-4)
162
Compound TgC
Nylon 66 +53
Polyethylene oxide -54
The Graft -581+55
Table (5-4) Glass transition temperatures of
Nylon 66, PEO, Nylon 66-g-PEO.
The graft showed two glass transitions correspond-
ing to the homOpolymer PEO and Nylon 66 respectively. So,
firstly, phase separation occureed in the grafted material.
Since the sample was metalated 30% and contained 28% w/w
PEO, there must have been on average about two units of
ethylene oxide per branch. One cannot expect a Tg for
such short branches, so there must be some longer branches
of PEO in the graft copolymer.
The glass transition temperature for a graft
copolymer, containing a higher content of ethylene oxide
57% w/w, and with 30% metalation, as before, were also
measured Figure (5-9). As well as the Tg corresponding
to the PEO, an additional peak was observed, while the
signal peak corresponding to the Tg of nylon was weaker
than that for the lower PEO graft copolymer. The graft
copolymer was split into two fractions, soluble and
insoluble, in methanol. Glass transition temperatures
of both fractions were measured and are shown in Figure
(5-10). The fraction containing 70% w/w PEO, which was
soluble in methanol, behaved thermally in a manner
similar to that of the complete graft copolymer. An
additional peak was again observed and the Tg for nylon
was not noticed. But the thermal character of the
insoluble fraction was similar to the graft copolymer
containing 28% w/w PEO. For the latter material the
163
additional peak was not observed. The additional peak
observed in the thermoanalyser trace, for the graft
copolymer containing a relatively high PEO content
was attributed to the crystallinity of the PEO grafts.
This is discussed further in the next section.
.1.46 -76 -t• -415 -70 I; 0 i5 r. 45 60 14 oC
164
-7o -6D .45 -T• -45- 0 16 7• AC r• x5 C
Figure (5-8) - Thermogram of Nylon 66-g-PEO (PEO 28% w/w metalation 30%)
Figure Thermogram of Nylon 66-g-PEO (PEO 57% metalation 30%)
165/
I
-/o -14" .4 -45 -30 .t6 0 tc 30 46
Figure (5-10)A - Thermogram for the soluble fraction in Me0H (Nylon 66-g-PEO)
-1 - L. .45 -To -If 0 I 3e 45 6O 75
Figure (5-10)B - Thermogram for the insoluble fraction in Me0H (Nylon 66-g-PEO)
166
5.2.4.6. Crystallinity
Most nylons are partially crystalline. They
are different from many other crystalline polymers, such
as polyethylene, in that the degree of crystallinity of
a given nylon can be controlled over a wide range. High
crystallinity requires both parallel alignment of the
chains and uniformity in the manner in which hydrogen
bonds are formed. The simplest classical concept of
morphology is a nearly perfect crystalline phase embeded
in an amorphous entanglement of chains with many chains
joining the two phases. The actual morphology is more
complicated than this simple concept. However, the
concept provides a simple quantitative description of
morphology from which the percentage of crystallinity
can be derived.
Since, in the second part of this research,
the influence of heterogeneous media is likely to influence
the structure of the reaction product, attempts were made
to determine the percentage of crystallinity of the starting
materials by density measurements and the use of X-ray
diffraction techniques.
During purification nylon samples were dissolved
in formic acid and then precipitated from methanol-water,
as described in the experimental section. It was important,
therefore, to check if there had been any change in the
degree of crystallinity due to this procedure. The
percentage of crystallinity of a nylon sample is dependent
on the thermal history of that sample. To determine the
167
degree of crystallinty by IR spectroscopy229 a film
must be prepared carefully. Preparation of a film
from the precipitated nylon powder involves the melting
or dissolving of the sample. IR spectroscopy is thus
not a good method for the determination of the percentage
crystallinity of the precipitated sample.
Generally the polymer diffraction patterns
obtained by X-rays are of poor quality compared with
those obtained from low molecular weight crystalline
materials. The Nylon 66 diffraction pattern is of
very poor quality and the resolution of the few diffraction
spots is not good.230
The polymer diffraction patterns are
also variable. Thus the positions and sharpness of the
diffraction patterns may vary. These variations are a
function of the history of the sample.230
. Hence X-ray
diffraction is not a good method for the determination
of the percentage crystallinity of nylons. In Figure
(5-11), the X-ray diffraction pattern of a series of
Nylon 66 samples, treated in different ways, are shown.
No attempt was made to determine the percentage
crystallinity of the samples from the X-ray data. The X-
ray pattern showed a shift in position after precipitation
of the sample [patterns A and C, Figure (5-11)]. This
type of transformation had been reported when the thermal
history of Nylon 66 was altered. For example, when oriented
Nylon 66 fibres were heated to a high temperature under zero
tension, some of the molecules changed from the elongated to
the folded conformation.231
Comparison of patterns A and B
in Figure (5-11) showed that the supplied nylon was not
drawn. The observed shift after precipitation could not be
explained.
168
Figure (5-11) - X-ray Diffraction Patterns 4mm = 109
A is the X-ray diffraction pattern of a sample of Nylon 66(ICI) prepared by slicing with a sharp knife
B is the pattern for a sample of Nylon 66 which melted and cooled slowly
C is the pattern for Nylon 66 dissolved in HCOOH precipitated from methanol-water and dried as described before
D is the diffraction pattern of sample C after melting and cooling slowly
E is the pattern for sellotape
Guinier-de Wolf focussing camera was used.
169
The density measurement method is not an absolute
one for the determination of the percentage crystallinity
of a polymer. An unsuccessful attempt was made to determine
density of precipitated nylon 66. Due to the difficulty of
wetting individual powdered polymer particles and their small
size, a wide range of density was obtained and this experimental
method was not continued.
The thermograms shown in Figure (5-12) illustrating
the behaviour of nylon 66 on melting and cooling from the melt
have been reported.186
Fast cooling from the melt gave the
result shown in Figure (5-12)(a), indicating complete absence
of crystallization. Slow reheating gave the thermogram shown
in Figure (5-12)(b). Exothermic crystallization followed by
endothermic melting occurred. On the other hand, slower
cooling from the melt resulted in normal freezing, Figure
(5-12)(c), and the freezing point depression was slightly
dependent upon the cooling rate.
A sliced sample of I.C.I. nylon 66 was used for the
determination of the melting point by DSC. The melting point
of the same sample was measured after dissolving it in formic
acid, precipitating it from Me0H- water and drying. The
results are shown in Figure (5-13). By comparison with
Figure (5-12), the exothermic peak in Figure (5-13)(b)
must be due to crystallization of nylon 66. Thus precipitated
nylon 66 has a lower crystallinity than unprecipitated nylon.
In Figure (5-14), Tg of a sample of nylon 66 before and after
O
COOLING. 10°C /MINUTE
HEATING, 10°C/ MINUTE
COOLING. 1°C/MINUTE
170
TEMPERATURE .'C s
100 200 300 400
Figure (5-12) - Thermogram of crystallisation of Nylon 66
171
precipitation is shown. The cells used in the DSC machine
attachment were of equal weight. The polymer samples were
also of equal weight. Both samples were dried at 60°C for
24 hours before measurements. Since Tg is a characteristic
of the amorphous part of a polymer, one would expect a
sharper transition at Tg, the lower the percentage crystall-
inity. The unprecipitated nylon sample did not show any
glass transition Figure (5-14) but Tg is notoriously
difficult to measure for partially crystalline Nylon 66
samples. A melting point was observed, as expected
Figure (5-13). However, thermal analysis of the precipitated
sample indicated a glass transition temperature Figure (5-14)
and a melting point Figure (5-13). This shows that
the precipitated nylon sample had a lower percentage
crystallinity than the unprecipitated nylon. The
manufacturer believed that the degree of crystallinity of
the nylon supplied was 30-40%. Thus the precipitated nylon
had a degree of crystallinity lower than 30-40%.
The existence of three differently shaped
spherulites has been reported for Nylon 66.232 A slice of . -2
unprecipitated Nylon 66 about-U/0mm thick was used for the polarizing microscope study. The resultant photograph is
shown in Figure (5-15). In the unprecipitated nylon,
numerous small spherulites were observed.
A sample of Nylon 66-g-PEO containing 57% w/w PEO
° (metalation 30%) was cooled to -90C and examined by DSC.
(co VW"
172
(a- )
b.
CC)
ie I.. 120 !ea Lo 220 34o 20. 2A, 300 LW
Figure (5-13) - Thermogram of Nylon 66 (a) a slice sample of ICI Nylon 66
(b) a precipitated sample of Nylon 66
(c) is sample (b) after slow cooling and reheating.
ID0 10 Po 40 (o 6. 76 . 0 fp 1.90
Figure (5-14) - Thermogram of Nylon 66 (a) an unprecipitated sample
(b) a precipitated sample
173
The PEO started to crystallize at about -35°C and then
melted at about 0°C Figure (5-9). The methanol soluble
fraction of the graft copolymer containing 70.8% w/w PEO
showed the same type of thermal behaviour. However, the
PEO in mem insoluble fraction did not crystallize and
then melt at the higher temperature Figure (5-10). When
the percentage of PEO was increased in the unfractionated
graft polymer, with constant metalation, the PEO
crystallized. For the unfractionated graft samples with
a lower percentage PEO but with the same percentage
metalation, crystallization and subsequent melting of PEO
did not occur. Unsuccessful attempts were made to observe
the spherulites of PEO in the graft copolymer using a
polarizing microscope and films cast from a solvent.
Penetration of water into the film on cooling in liquid
nitrogen prevented optical success being made.
The melting points of a sample of the graft
copolymer containing 57% w/w PEO (metalation 30%) could
not be measured by DSC, since the PEO started to decompose
at about 170°C Figure (5-16).
5.2.4.7. Solution Properties of the Graft Copolymer
115P In Figure (5-17), and the logarithmic .
jiAscosity number (lnflr)/C are plotted against concentration
for pure Nylon 66, Nylon 66-g-PEO (PEO 28% w/w), Nylon 66-
g-PEO (PEO 57% w/w) and low molecular weight PEO (molecular
weight less than 5000), in HCOOH at 25°C. Since backbone
degradation during the preparation of the graft copolymer
was minimal, one might predict an increase in [fl ] for the graft copolymers with increase in molecular weight
relative to the backbone polymer, Nylon,66. However,
174
Figure (5-15) - A. photogral:.11 of Nylon 66 by a Polarizing Microscope
""T
Cl Jo 4c, go go )417 120 Ito f)
I 46 116 Boa
Figure (5-161 - Thermogram of Nylon 66 -PO (metalation 30% PEO 57% w/w)
175
•
Lgt
1.3 , •
oas
1.2
• •
•
•
0.9 o-
os. 'Ss
*Gs ss.
a- So.
g
• 0.4 0
• a
C
03 •
• 0-2,
- d
0.1
C/102gcm-3
o 0.1 0.4 04 al
Figure (5-17) - A,A' Nylon 66, B,B' Nylon 66-g-PEO (28% w/w PEO) C,C' Nylon 66-g-PEO (57% w/w PEO) D, D' low molecular weight PEO solvent formic acid at 25 C
Isp/c
lnlr/c
176
relative to Nylon 66 itself, increasing the molecular
weight of the graft copolymer caused a decrease in 01
Hence the grafted molecules were in a collapsed state in
HCOOH. The degree to which this collapsing occured
increased as the percentage of PEO was increased. The
degree of metalation for both of the grafted samples was
30%. The limiting viscosity number of poly(2-vinyl mnrridine) grafted with polystyrene has been studied233 in a mixture of
(toluene-ethanol) at 30°C. The limiting viscosity number
of the graft copolymer fell consistently below that of the
poly(2-vinyl pyrridine) backbone.
In Table (5-5)K', the Huggins constant, defined by
the equation: 234
Isp - [I] + iv[q]2C (5-20)
is shown for Nylon 66, PEO, unfractionated Nylon 66-g-PEO
and two fractions obtained from the graft copolymer.
Usually, but not always, K' has been reported to be in the
range 0.35 to 0.40.236
For this system K' was in the range
0.08 to 0.58. As the percentage of PEO w/w in the graft
copolymer was increased, the value of K' approached that
of K' for PEO. In the Huggins equation, K' depends on the
size, shape and cohesional properties of both solvent and
solute molecules and temperature. A satisfactory explanation
for the values of K' for a given system has not been given.235
In Figure (5-18)l_s lnIr _f
and are plotted against
concentration for nylon and the graft copolymer containing
57% w/w PEO (metalation 30%) in HCOOH at 25°C. Plots are also
Polymer [1)/g lcm+3 Slope/g -2cm+6 k
* Nylon 66 136.5 1596.6 0.085
Nylon 66-g-PEO (28% w/w PEO) 101.5 1759.2 0.170
Nylon 66-g-PEO (5? w/w PEO) 58.5 747.6 0.218
Insoluble Fraction 120.0 1384.8 0.096
Soluble Fraction 50.5 833.3 0.326
PEO 28.0 461.5 0.588
Table (5-5) - k , the Huggins Constant for Nylon 66, PEO and the Graft Copolymers. Metalation for the Graft Copolymers was 305.
* average
178
6
•
*N.
- - # - - — — — —
8
C. 0
0.7
e.2
6
c/lo2gcm-3 0 0.2 0.4 0.4 0.1 o.9
Figure (5-18) - A. Nylon 66 C. Nylon 66-g-PEO (PEO 57% w/w) B,B' the insoluble fraction of th: graft copolymer. DI D' the soluble fraction of the graft copolymer
nsp/c In solvent HCOOH at 2593'
179
shown for the fraction of the graft copolymer containing
70% w/w PEO (soluble in Me0H) and the fraction of the
graft copolymer containing 25% w/w PEO (insoluble in
methanol). As the percentage of PEO in the graft fractions
increased, [1] tended toward [ 1] of PEO. As one might
expect, [lei] of the graft copolymer was between the [1 ] values of the graft copolymer fractions.
The limiting viscosity number of a polymer
molecule in solution is proportional to the effective
hydrodyamic volume of the molecule in the solution divided
by its molecular weight. The effective volume is
proportional to the cube of a linear dimension of the
randomly coiled polymer.236 If (r2)1/2 is the dimension
chosen
01 = (I) (1-) 3/
(5-21)
2 2 . Replacing
(r2 1/2 1/2 r R ) by o((r.) and supposing that -- is a
function of chain structure, independent of surroundings or
molecular weight, it follows that
[1] =(p(r/M)3/2
K = () (r/m) 3/2
M 1/2 3 3 = KM1/2 cc (5-22)
(5-23)
where r. is the mean square end to end distance of a
molecule in the unpreturbed state,
2 i r is the mean square end to end distance of a polymer
in solution
M is the molecular weight of the polymer
Xis the expansion factor
and (I) is, to a good approximation, a universal constant.
180
Deis given by:
e 0(5 - 3 = 2Cm tg (1- 7i)M1/2 (5-24)
where M is molecular weight
O is the theta temperature
T is the absolute temperature
is the entropy parameter
and CM is a variable dependent on several
factors involving the nature of the
polymer in the solvent.
In Figure (5-19) the limiting viscosity number of
a formic acid solution of the graft copolymer containing
57% w/w PEO (metalation 30%) is plotted against temperature.
The limiting viscosity number of a methanol soluble
fraction of the graft copolymer is also plotted in Figure
(5-19) against temperature using Me0H as the solvent. As
the temperature is increased, the limiting viscosity number
falls. Since both K and cZ in equaticn (5-22) are
temperature dependent, separation of these factors using
available information for the system is complicated. The
differences in concentration at different temperatures,
due to solvent density changes, were allowed for by
considering the density variation of the solvent.
In Figure (5-20) the [n] of the graft copolymers containing 28% w/w and 57% w/w (both with metalation of 30%)
are plotted against the composition of the mixed liquids
181
o. g
(I) 0.7
0.6 •
0 5 .
Nl 040 E U
I to
_"""` 0.1
N O H 0.2
0.1
0 10 Io 7D 4• fo fo 7o go
Figure (5-19) - Limiting viscosity number against temperature. A. Nylon 66-g-PEO (PEO 57% w/w) solvent HCOOH B. The Me0H soluble fraction of the graft copolymer solvent Me0H
cu
182
v/v. Water was employed as a non-solvent and formic acid
as the solvent at 25oC. Above 15% v/v water, the graft
copolymer was not soluble in the mixed liquids. However,
progressive addition of water, which is a non solvent for
the backbone, caused a collapse of the graft molecules and
a consequent rapid reduction on limiting viscosity numbers.
The effect of addition of water to a solution of PEO in
HCOOH produced a smaller lowering of [1]. This is
expected since water is a much better solvent for PEO than
it is for the graft copolymers.
5.2.5. The Graft Copolymer of Nylon 66 Polyacrylonitrile (Nylon 66-g-PAN)
5.2.5.1. Solubility
The graft copolymer was split into two main
fractions. One fraction was soluble in DMF and the other
was insoluble in DMF. A sample containing 64.5% w/w PAN
(metalation 30%) was fractionated 59.8% w/w; of the sample
soluble in DMF, 40.2% w/w was insoluble in DMF but was
soluble in HCOOH. Some particles in the latter solution
appeared to be jelly-like. The fraction soluble in DMF
was dissolved in this solvent and split into three sub-
fractions by the addition of HCOOH as non-solvent. The
IR spectrum of each sub-fraction was obtained by casting
a film from a DMF solution onto a NaC1 disc and drying for
24 hours in a vacuum oven at 60oC. The IR spectra of the
above sub-fractions were identical. Each sub-fraction
showed a‘CO absorption band which confirmed the presence
of the nylon backbone. Homopolymcr formation in this
type of metalation is generally negligible and the above
IR results are in agreement with this.
183
(11
14.)
U 1.0
ea
1.-"A 6.9
CU
0 H 0.7
0.4
0.3
0.2
04
0
so 36 composition of mixed solvent vrviS
Figure (5-20) _411 against the compositiOn of mixed solvent A. Nylon 66-g-PEO (PEO 28% w/w) B. Nylon 66-g-PEO (P10 57% w/w) C. low molecular weight PEO HCOOH as solvent, H2O as the non-solvent.
184
5.2.5.2. IR Spectra
The IR spectrum of the graft copolymer (containing
64.5% w/w PAN metalation 30%) shown in Figure (5-21), was
obtained using a KBr disc. The spectrum showed an absorption
band at 2250cm-1
corresponding to -CmN absorption. In the
IR spectrum of the fraction of this material soluble in DMF,
the -N-H absorption band at 3300cm1 was absent, indicating
that the backbone was fully metalated Figure (5-22). In the
IR spectrum of the fraction which was insoluble in DMF,
-CmN absorption was not observed and the IR spectrum was thus
similar to that of Nylon 66.
5.2.5.3. Thermal Degradation of Nylon 66-q-PAN -Complete Conversion of Acrylonitrile
The Nylon 66 PAN graft copolymer was a white powder.
The grafting reaction was exothermic and in each experiment,
all monomeric acrylonitrile was consumed. The percentage of
grafting (w/w) was determined by nitrogen microanalysis and
also by the increase in weight. The colour of the graft
copolymer in DMF changed to a yellow-orange colour faster
than the acrylonitrile homopolymer, both at room temperature
and at about 50oC. It is known that the colour of PAN may
be changed if it is heated over 140°C. Various authors
have studied the structure of discoloured PAN and have
suggested different structures. Structure (5-25) was
proposed by Houtz.237
4•
,1.85
114
80
61)
t o
I 1 I I 1 35o. ;Doi 25•s logo 'coo lo.e 67.5
—1
Figur'e(5-21) — The IR Spectrum of Nylon 66-g-PAN (metalation 30% PAN 64.5% w/w) KBr disc:
4000 3 600 3ao• 2.5o Zoos If o. 100*
4.20 lac
Figure (5-22) - The IR Spectrum of the DMF soluble fraction of Nylon 66-g-PAN - Cast a film from DMF
186
H H H
\cl-'c ■c .,...-
c ,....
c .\ .
C C 1 If ' 1 (5-25)
C . C \I\T - N NI.
Schurz et al238,239 suggested the structure (5-26)
-CH-CH -CH-CH -CH-
2 , 2 1 CN C=NH CN
-CH-CH2-C-CH2-CH- 1 1 CN CN CN
(5-26)
A partially hydrogenated ring structure has been proposed
by McCartney:240
CH H CH CH 2‘e
" C
I\T"*.
(5-27)
Fester241
assumed'a structure of the type:
-CH=C-CH=C-CH=C-CH=
CN CN CN (5-28)
It is difficult to explain the accelerating influence of
the nylon backbone on the PAN discolouration reaction,
in view of the present controversy concerning the
structure of the degraded PAN.
5.2.5.4. Thermal Analysis of a Sample of Nylon 66-q-PAN
The graft copolymer of Nylon 66 PAN (containing
64.5% w/w PAN, metalation 30%) had a Tg corresponding to
the Nylon 66 backbone at about 45°C, but PAN in the graft
copolymer started to discolour about 100°C, Figure (5-23),
before its Tg could be observed.
5.2.6. Metalated Nomex
In Nomex, the hydrogen atoms in the amide groups
are more reactive than the hydrogen atom in the amide of
Nylon 66. Thus, the amide hydrogen atom in Nomex is
more acidic than that in Nylon 66, since the electrons of
the nitrogen atom in Nomex can take part in the resonance
of the aromatic ring.
187
188
-N H 0 1 It
H 0 7 u
= N-C
0
0 11
C - H -N E) H 0
N-C
H
0 II
C-
0 C-,
H
(5-29)
Nomex was metalated up to 95% (based on numbers) by Na/NH3
solution and 30% by sodium naphthalene. However, metalation
of nylon 66 by sodium naphthalene to this extent was not
possible. Metalated Nomex is a relatively stable red compound
and under normal conditions such as storage in a specimen tube
equipped with a cork, no significant colour change was
observed for several days. The stability of metalated Nomex
is due to the following resonance forms:
9H Q. -C N- -C. 0 N-
-C-N- 9 ...
-C-N- 0
0-c
0
H (5-30)
0 -C-N=
-C O
-C-N=
Metalated Nomex was insoluble in DMF and the parent compound,
Nomex,could be regenerated by the addition of dilute aqueous
acid solutions.
189
Degradation of Nylon 66 during metalation under
appropriate conditions was negligible. Metalation of
Nomex up to 75% took only about 1 hour, the reaction being
much faster than that for Nylon 66. Du Pont, the
manufacturers, claimed that Nomex was unaffected by
treatment with a 10% w/w solution of sodium hydroxide
for 100 hours. The degradation of Nomex could not be
studied due to the lack of a suitable solvent. However,
one would not expect a great deal of degradation of Nomex
below about 80% metalation, since the Nomex during the
metalation reaction was not in contact with ammonia for
a long period. Again traces of sodium hydroxide would not
be expected to cause much degradation.
5.2.6.1. Nomex-g-Polyacrylonitrile
The IR spectra of Nomex-g-PAN (metalation 90%, 60%
w/w PAN) and pure Nomex are shown in Figures (5-24,25).
The graft showed absorption bands at 2250cm-1 (for -CmN)
and at 2950cm-1 (for -CH2-9 • The reaction of
acrylonitrile with metalated Nomex was quantitative, the
percentage of grafting being determined both by the increase
in weight and by nitrogen microanalysis. A sample of the
graft containing 60% w/w PAN (metalation 90%) was split into
two main fractions, one soluble and one insoluble in wet
nitromethane (about 5% water w/w). 51% w/w of the graft
was soluble in wet nitromethane, which is a solvent for
polyacrylonitrile and a non-solvent for Nomex. The
nitrogen microanalysis showed the insoluble fraction
190
contained 17.7% w/w acrylonitrile grafted onto the Nomex.
Another sample of the graft was split into two fractions,
one soluble and the other insoluble in DMF. The fraction
of the graft soluble in DMF was split by partial
precipitation at 300C into eight sub-fractions of
approximately equal weight. Methanol was chosen as the
non-solvent. The IR spectrum of each fraction showed
absorption bands for -C=N groups, aromatic rings and 9 -C- groups. Thus homopolymeric PAN was not present in this
system. Nitrogen microanalysis was carried out on each of
the eight sub-fractions and the following results
No. of Sub-Fraction Nitrogen %
obtained:
Grouping of Sub-Fractions
I
II
III
IV
V
VI
VII
VIII
23.80)
24.00)
25.16)
25.65)
24.14)
24.18)
24.42)
23.90)
23.90
25.40
24.16
(I)
(II)
(III)
The eight sub-fractions were combined to form
three groups, I-III, containing on average 23.90%, 25.40%
and 24.16% nitrogen. DMF is a poor solvent for Nomex but
is a good solvent for PAN. Using previous results, the
following comments may be made about the three groups of
sub-fractions, I-III:
191
I
0 15 1s 4. 4- t. ZS /.6 loc 126 (74'
Figure (5-23) - Thermogram of Nylon 66-g-PAN (PAN 65% w/w metalation 30%)
406o
3Cop 3000 240 • 2400 4o. loos doe
Figure (5-24) - The IR S-rectrum of Nomex-g-PAN KBr disc ( metalation 90% pAN 600Aw/w)
(5-31) H N- I
0 --C -N
CH2
192
The first group, I, contains high molecular
weight Nomex and the extent of grafting is
relatively small.
(B) The second group of combined sub-fractions,
II, contains high molecular weight Nomex
which has been grafted to a greater extent
than I.
(C) The third group of combined sub-fractions
contains low molecular weight Nomex which
has been grafted to a greater extent than
II.
Pure Nomex showed a glass transition at 85oC, but
the graft copolymer showed a glass transition at 66°C, and
degradation of PAN occurred at 110°C. A solution of this
graft copolymer in DMF at room temperature acquired a
yellow colour due to degradation of PAN faster than a
solution of the homopolymeric PAN under similar conditions.
5.2.6.2. N-Benzyl Nomex
N-benzyl Nomex was prepared according to the
reaction:
9 H
-C N-
I 0 Na
-C-N o + C6H5CH2Br
0 11
-C
NaBr +
193
The end of the reaction was determined by
observing the disappearance of the red colour. The IR
spectrum of the product showed absorption bands at 2950cm-1
for —CH2- Figure (5-27). Nitrogen microanalysis gave the
following results:
C 66.40%
H 5.38%
N 6.50%
The percentage of nitrogen present indicated 65%
benzylation (on a numbers basis). Only 10% of the metalated
centres were destroyed by impurities in the benzyl bromide. Thus
since handling benzyl bromide needs special care, it was
used without further purification. The reaction showed that
all the metalated centres were available for benzylation.
N-benzyl Nomex showed a glass transition at 80°C.
5.2.6.3. Unsuccessful Attempts to Prepare Nomex-q- Poly(ethylene-oxide), Nylon 66-q-Polystyrene; The Metalation of Poly acrylamide
Since the electrons on the nitrogen atom in
metalated Nomex may take part in the resonance of the
aromatic ring Equation (5-30), these electrons are
more delocalized than in metalated Nylon 66. Thus
metalated Nomex is not a strong enough nucleophile to
attack ethylene-oxide.
The ease with which the monomers undergo anionic
polymerization increases in the order:242
Mv„ 1 too
.go
6o
40
1F.
194
to•
'a
110
245
Irmo 36•• 3000 2400 •
ZNo.
11%
1500
Figure (5-25) - The IR Spectrum of Nomex, KBr disc
4ov° 30e* 30D• 2.5oo gas► Qat) ' ,too Ioo• VD _1
Figure (5-26) - The IR Spectrum of N-Benzyl Nomex, cast a film
195
butadiene <isoprene styrene methacrylate
vinyl chloride 4(acrylonitrile
The attempt to prepare Nylon 66-9-Polystyrene was unsuccess-
ful because styrene is less reactive than acrylonitrile
and is not reactive enough to react with metalated Nylon
66 under the conditions employed.
Since metalation of simple primary amides has been
reported,243
one might expect metalation of polyacrylamide
to occur. However, an attempt to achieve 30% metalation of
polyacrylamide under the conditions previously described
failed and no evidence of metalation was found.
5.3. Influence of Heterogeneous Media on the Nature of the Reaction Products
5.3.1. Introduction
Styrene has been grafted onto Nylon 66 using
radiation and it was reported that the grafting occurred on
the surface of the nylon fibre.176
Several vinyl polymers have been grafted onto Nylon
66 using ceric salts as initiators in heterogeneous media.
Apparently polymerization was restricted to the surface
regions due to slow diffusion of the initiator into the
fibre. Staining with a solution of aniline in dilute
hydrochloric acid showed that penetration of the ceric
salt into the fibres was only superficial when the latter
196
were soaked in a 0.5N ceric ammonium sulphate solution.
A solution of ceric ammonium nitrate in nitric acid
penetrated the nylon more rapidly and was distributed,
though not uniformly, throughout the fibres.199
A graft copolymer of poly(methyl methacrylate-g-
styrene) has been prepared by the addition of living
polystyrene in THE to a solution of poly(methyl-methacry-
late).81
Only a small percentage of the ester groups
reacted. This was probably due to the collapse of the
partially grafted copolymer to form an inner shell of
poly(methyl-methacrylate) and an outer shell of polystyrene.
This meant that only those ester groups on the surface of
the collapsed structure were available for grafting.
However, it was claimed84
that the grafting of living
polystyrene to poly(methyl-methacrylate) is not a random
process, but occurs preferentially on molecules of
poly(methyl-methacrylate) that-have already reacted. Since
poly(methyl methacrylate) molecules may be uncoiled as a
result of the grafting process, the ester groups of the
partially grafted molecules are more accessible and further
grafting may then occur more readily.
5.3.2. Influence of Heterogeneous Media on Nylon Systems
In an ideal ionic polymerization initiation must
be rapid compared to propagation, so that all the growing
chains become available at approximately the same time.
Each polymer chain will have an equal chance to add
monomer, so that all of the resultant chains should
197
have an equal size. However, the following results
show that the graft copolymers of nylons which were
prepared on the heterogeneous media contained grafted
chains of different lengths and, in some cases, not
all of the metalated centres were able to act as
initiators.
(1) There was a linear relation between the
percentage of metalation (based on
numbers) and the percentage of grafting
(w/w) up to about 30% metalation. Above
30% metalation, curVere was observed
Figure (5-5). This provides evidence
that the metalated sites at the centre
of the nylon particles are not as
accessible as the ones at the surface.
(2) A sample of Nylon 66-g-PEO (28% w/w PEO,
metalation 30%) showed a glass transition
for PEO Figure (5-8). Ideally, all the
metalated centres would react with PEO
at the same rate so that there would be
about two units of EO per branch. One
would not expect a glass transition for
such short branches of ethylene oxide.
So there must be some longer chains.
(3) A sample of the graft copolymer of Nylon 66
poly(ethylene-oxide) containing 57% w/w PEO
(metalation 30%) was split into two fractions,
one soluble and one insoluble in NeOH.
198,
Nitrogen microanalysis showed the soluble
fraction to contain 70.8% w/w PEO and the
insoluble fraction 25% w/w PEO.
(4) In the IR spectrum of the soluble fraction
of the graft copolymer of Nylon 66-PAN
(64.5% w/w PAN 30% Me) the _n_ absorption
band at 3300cm-1 was missing whilst the
IR spectrum of the insoluble fraction was
similar to that of original Nylon 66
Figure (5-22).
As the original Nylon 66 had a lower crystallinity
after precipitation from Me°H/water, the effects due to
crystallinity are probably very small. The following scheme
may be suggested in order to explain the above results:
(1) In the IR spectrum of the soluble fraction
of Nylon 66-g-PAN the _n_ absorption band at
3300cm-1
was missing, so the rate of metalation
at the surface of the particles was greater
than the rate of metalation inside the particles.
(II) In the preparation of N-benzyl Nomex, it was
shown that all the metalated centres were able
to react with benzyl bromide under the
experimental conditions. Since the graft
copolymer contained grafted chains of different
lengths, the rate of reaction of the metalated
centres with the monomer was greater at the
surface of the particles than inside the
particles.
199_
(III) A metalated centre of a nylon is generally
insoluble in the reaction medium. However,
when this metalated centre has reacted with
one or more monomer molecules, the new centre
becomes soluble in the surrounding liquid
media. Therefore, it may be assumed that
the new anionic centre will react more
readily with other molecules of monomer
than the unreacted metalated centre.
(IV) In the case of acrylonitrile, (AN), the
monomer is much more reactive in anionic
polymerization than in the case of ethylene
oxide (EO). Therefore the polymerization
of AN was carried out in a methanol solid
CO2 bath at about -30
oC while the preparation
of Nylon 66-g-PEO was performed at 60°C. As
a result of this difference in the temperature,
the rate of diffusion of monomer to both the
anionic centres on the surface of the nylon
particles and to the anionic centres inside
these particles, is expected to be lower in
the case of AN than EO. PAN is insoluble in
its own monomer, so PAN chains may act as a
shield against further diffusion of AN into
the nylon particles.
(V) Although the AN monomer is much more reactive
towards anionic polymerization than EO the
possibility of reaction of AN with a metalated
200
site in the interior of the nylon particles
is less than for EO due to the shielding
effects and temperature differences. In
other words, AN may more easily react with
a growing centre on the nylon surface than
EO under these conditions. This also implies
that the EO molecules may penetrate the nylon
particles to a greater extent than AN.
201
6. CONCLUSIONS
Although ammonia is frequently used as a solvent
in both inorganic and organic chemistry, its application
in the study of ionic polymerizations has been limited.
In the present work, solutions of sodium in
liquid ammonia have been successfully used to metalate
nylons and then to synthesize various graft copolymers.
One of the advantages of this newly developed metalation
procedure is that the end of the metalation reaction may
be precisely determined by the disappearance of the blue
colour characteristic of the sodium/ammonia solutions.
A specially designed pressure vessel has been developed
to facilitate the handling of the reagents used in
metalation studies. There are no metalation by-products,
so that formation of homopolymer is negligible. Using
this metalation procedure, Nylon 66, Poly(hexamethylene
adipamide) has been successfully grafted with both
Poly(ethylene-oxide) and polyacrylonitrile. The aromatic
nylon, Nomex, has been used to synthesize the graft
copolymer with polyacrylonitrile. The N-benzyl derivative
of Nomex was also prepared. Some physical properties
of these graft copolymers have been studied, although
fractionation was sometimes necessary.
Grafting in this system occurs to a large extent
on the surface of the particles so that this method could
202
be used industrially, for example, for the preparation
of fibres with antistatic properties. Unfortunately,
the lengths of the graft chains formed by this
technique are different, so the graft copolymers may
not be considered as model macromolecules in
characterization studies.
Some of the mechanical properties and the
insolubility of nylons are due, in part, to hydrogen
bonding. In the previous free radical methods of
preparing graft copolymers of nylons, the hydrogen
atoms of the amide groups were unsubstituted. Using
the metalation method reported in this study, the
hydrogen atom of the amide groups may be readily
replaced by a variety of substituents, including
polymeric chains.
Further work involving other monomers and
nylon systems is both possible and worthwhile. Also
metalation of polymers, such as polyurethane, would
enable other graft copolymers to be synthesized and
studied. X-ray crystallographic studies of N-derivatives
of nylons and graft copolymers would be of interest. The
heavy N-substituted derivatives of nylons are of
particular importance in this area.
203
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