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LIST OF ABBREVIATIONS:
1. AN-Acrylonitrile2.
AA-Acrylicacid
3. AAm-Acrylamide4. PAN-Polyacrylonitrile5. MA-Methylacrylate6. MMA-Methyl Methacrylate7. PEG-Polyethylene Glycol8. NCTB-N-Cetyl-Trimethyl Ammonium Bromide9. CTAB-Cetyl-Trimethyl Ammonium Bromide10.CAN-Ceric Ammonium Nitrate11.CAS-Ceric Ammonium Sulphate12.CA-Citric Acid13.CS-Ceric (IV) Sulphate14.LA-Lactic Acid15.CMC-Critical Micelle Concentration16.SDS-Sodium Dodecyl Sulphate17.[ ]Concentration18.I-Ionic Strength19.oC-Temperature In Degree Celcius20.K-Degrees of Kelvin21.Rp-Rate of Polymerisation22.Ri-Rate of Initiation
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CHAPTER-I
1.Introduction
Macromolecules or polymers are very high molar mass compounds
consisting of several structural units inter-connected by covalent bonds. The
molar mass of a polymer may vary from 5,000 to several millions.
Fundamentals research in polymer chemistry was done from 1920 to 1950 by
the German chemist,Hermann Staudinger who won the 1953 chemistry Nobel
prize. Karl Ziegler,Giulio Natta and Paul J.Flory also made signifigant
contributions to the polymer chemistry. Flory was awarded the 1974 chemistry
Nobel prize. P.G.de Gennes, the French physicist was awarded the 1991
physics Nobel Prize for studying polymer liquid crystals and developing the
scaling concept in polymer dynamics.
A polymer consists of a large number of simple monomeric structural
un which are repeated over and over again to form a giant molecule called a
macromolecule. The simple unit is called the repeat unit. In the polymers -A-A-A-A-A-A- and -A-B-A-B-A-B- for instance, the repeat units are A and A-B
respectively. A high polymer is one in which the number of repeating units is
in excess of about 1000. This number is termed as Degree of
polymerization.
Polymers find immense use in glass and ceramics industries. They
are also being employed for rocket constructions polymer engineering deals
with the splitting up of natural high molar mass compounds to produce
valuable food stuffs. The hydrolysis industry, for instance,produces ethyl
alcohol by hydrolysis of wood.
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2. Types of polymer and polymerization
One classification based on polymer structure and divides polymers into
condensation and addition polymers. The other classification is based on
polymerizations mechanism and divides polymerization into step and chain
polymerizations. The condensation addition classifications is based on the
composition or structure of polymers. The step-chain classification is based on
the mechanism of polymerization.
Vinyl monomers can be made to react with themselves to form polymers
by conversion of their double bonds into saturated linkages.
nCH2=CHY ( CH2CHY ) n
Where Y can be any substituent group such as hydrogen, alkyl, aryl,
nitrile, ester, acid, ketone, ether and halogen.
Condensation polymer and its synthesis involve the elimination of small
molecules, or it contains functional group as part of the polymer chain its
repeating units locks certain atoms. That is present in the monomer to which it
can be degraded.
2.1 Radical chain polymerization
It consisting of a sequence of three steps initiation, propagation, and
termination. The homolytic dissociation of an initiator species I to yield a pair
of radicals R.
KdI 2 R
Kd rate constants for catalytic dissociation. Then the addition of this
radical to the first monomer molecule to produce the chain initiating radicalM1.
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K1
R+ M M1
M-monomer molecule, k1- rate constant for initiation step. Propagation
consist of the growth M1
by successive additions of large number of monomer
molecules
Kp
M1+ M M2
Kp
M2+ M M3
etc.
Kp
Mn
+ M Mn+1
Kp rate constant for propagation. Termination occurs by a combination
of coupling and disproportionation.
Ktc
Mn+ Mm
Mn +
m
KtcMn
+ Mm
Mn
+Mm
Ktc & Ktd are the rate constant for termination by coupling and
disproportionation respectively.
2.2 Initiators
The initiation of the polymer chain growth is brought about by free
radicals produced by the decomposition of compounds called initiators. The
term chain growth represents a process involving a continuous and very rapid
addition of the monomer units to form polymer molecules or polymer chains.
As more and more monomer units are added, the length of the polymer chains
increases continuously and the chain growth rapidly.
A variety of initiators system can be used to bring about the
polymerization radicals can be produced by a variety of thermal,
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photochemical & redox methods. [Banford, 1998; Denisova et.al., 2003;
Eastmond., 1976 a, b, c; Moad et.al., 2002]1.
2.3 Thermal Decomposition of Initiators :
Types of Initiators :
The thermal, homolytic dissociation of initiator is the most widely used
mode of generating radicals to initiate polymerization. Polymerizations
initiated in this manner are often referred to as thermal initiated or thermal
catalyzed polymerizations.
The number of different types of compounds that can be used as thermal
initiators is rather limited one is usually limited to compounds with bound
dissociation energies in the range 100-170 KJ Mol-1
.
Compounds with higher or lower dissociation energies will dissociate
too slowly or too rapidly. Several different types of peroxy compounds are
widely used [Sheppard]2 these are peroxides such as acetyl and benzoyl
peroxides.
O O O
CH3-C-O-O-C-CH3 2CH3- C-O ----------------1
O O O
-C-O-O-C- 2-C-O ----------------2
The value of decomposition rate constant Kdvaries in the range 10-4
-10-9
S-1
, depending on the initiator temperature [East Mond, 1976, a,b,c]3. Most
initiators are used at temperature where Kdis usually 10-4
-10-6
S-1
.
Kd is larger for acetyl peroxides than for alkyl peroxides since the
RCOO radical is more stable than the RO
radical and for R-N=N-R, Kd
increases in the order R=allyl, benzyl > tertiary > secondary > primary
[Koenig, 1973]4.
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2.5 Types of Redox initiators:
Peroxides in combination with a reducing agent are a common source of
radicals; for example; The reaction of hydrogen peroxide with ferrous ion
H2O2+ Fe2+ HO+ HO+ Fe3+.
Ferrous ion also promotes the decomposition of a variety of other
compounds including various types of organic peroxides.
Fe2+
ROOR RO+ RO
----------------- 6
Fe2+
ROOH HO
+ RO
----------------- 7
O O
Fe2+ROOCR RCO
+ RO
----------------- 8
Other reductants such as Cr2+
, V2+
, Ti3+
, Co2+
and Cu2+
can be employed
in place of ferrous ion in many instances most of these redox systems are
aqueous or emulsion systems.
The combination of a variety of inorganic reductants and inorganic
oxidants initiates radical polymerization, for example,
-O3S-O-O-SO3+ Fe
2+ Fe
3+ + SO4
2 + SO4
-O3S-O-O-SO3+ S2O3
2 SO4
2 + SO4
+ S2O3
Other redox systems include reductants such as HSO3, SO3
2, S2O3
2in
combination with oxidants such as Ag+, Cu
2+, Fe
3+, ClO3
and H2O2.
OrganicInorganic redox pairs initiate polymerization, usually but notalways by oxidation of the organic component, for example for oxidation of an
alcohol by Ce4+
.
R-CH2-OH + Ce4+
Ce3+
+ H+ + R-
CH-OH (Or)
By V5+
, Cr6+
, Mn3+
[Fernandez and guzman 1989; Misra and Bajpai,
1982; Nayak and Lenka, 1980]6.
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There are some initiator systems in which the monomer itself acts as one
component of the redox pair. Examples are thiosulphate plus acrylamide or
methacrylic acid and N,N-dimethylaniline plus methyl methacrylate
[Manickam et.al., 1978; Tsuda et.al., 1984]7
.
2.6 Photochemical initiation:
Photochemical or photoinitiated polymerizations occurs when radicals
are produced by ultraviolet and visible light irradiation of a reaction system
[Oster and yang., 1968; pappas, 1988]8.
In general, light absorption results in radical production by either of two
pathways;
Some compound in the system undergoes excitation by energyabsorption and subsequent decomposition into radicals.
Some compound undergoes excitation and excited species interacts witha second compound to form radicals derived from the latter and / or
former compound.
2.7 Metal ion Oxidants in Redox Initiation:
Numerous reduction agents like alcohols, thiols, ketones, aldehydes,
acids, amines and amides have been used in combination with oxidizing metal
ions to participate in general singleelectron transfer reaction for free radical
polymerization, metal ion used mainly for this purpose are Mn(III) and
Mn(VII), Ce(IV), V(V), Co(III), Cr(VI) and Fe(III).
2.8 Cerium (IV) and electro induced polymerization
Cerium (IV) ion has been used for the oxidation of many organic
compounds, in the form of ceric(IV) ammonium nitrate (CAN), Ceric(IV)
ammonium sulphate (CAS), Ceric(IV) Sulphate (CS) and cericperchlorate and
the mechanism of such cericperchlorate and the mechanism of such reactions
has been well established.
Reducing agents, combined with Cerium(IV) and alcohols, aldehydes,
acids and amines. The rate of vinyl monomers were in the order of Ceric
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perchlorate > Ceric nitrate > Ceric sulphate. Which is in the order of oxidation
power of mentioned species.
Ceric ions forms complexes with amines such as sulfate, nitrate and
hydroxyl in aqueous solution whose relative concentrations have been found to
be function of hydrogen ion, respective anion concentration and ionic strength.
Increase of ligand concentration X = SO42
and NO3depress the rate of
polymerization due to formation of less reactive cerium (IV) species, CeXn
than Ce4+
and Ce(OH)n.
The mechanism and kinetics of polymerization involving ceric ion alone
[Ananthanarayan and santappa et.al]9 and also in combination with reducing
substrates such as alcohols10
, diols11
, polyols12
, aldehydes13
, ketones14
and
amines15
etc. with different monomers acrylonitrile, acrylamide and methyl
methacrylate etc.
2.9 Redox Polymerization:
The kinetics of redox polymerization in terms of the propagation and
termination steps. Termination is by biomolecular reaction of propagating
radicals; The initiation and polymerization rates will be given by the
expressions.
Ri= Kd[reductant] [Oxidant] -----------------9
Kd[Reductant] [Oxidant] 1/2
Rp= Kp[M] ----------10
2Kt
In the alcoholCe4+
system termination occurs according to
Mn+ Ce
4+ Ce
3++ H
+dead polymer ------------11
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At high ceric ion concentrations. the propagating radical losses a
hydrogen to form dead polymer with C=C and group.
Ri = Kd[Ce4+
] [alcohol] --------------12
Rt = Kt[Ce4+] [alcohol] ---------------13
Steady state assumption (Ri= Rt) one obtains the polymerization rate as
KdKp[M] [alcohol]
Rp= ----------14
Kt
Rpwill show a higher dependence on [M] in these cases then indicated
by the equation 2 and 5. The first dependence of Rion [M] results, in 3/2 and 2-
order dependence of Rp on [M] for biomolecular and monomolecular
terminations respectively. Organic inorganic redox pair initiate
polymerization, usually but not always by the oxidation of organic component.
For example : Ce4+
, V5+
, Cr6+
, Mn3+
, Ag+, Cu
2+ and Fe
3+ are used as the
initiator of the redox systems. There are some initiator systems in which
monomer itself act as a one component of redox pair. Examples, thiosulphate
plus acrylamide or metharylic acid and N, N- dimethylaniline plus methyl
methacrylate.
Initiation :
K1
M + R
M1
---------------15
Propagation :
Kp
M1+ M M2
----------------16
Kp
Mn-1
+ M Mn
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Termination
Kt
Mn + Ce(IV) Mn+ Ce (III) + H
+ ---------17
Oxidative Termination :
KpR
+ Ce(IV) oxidation product + Ce (III) + H
+ ---------18
In the methyl methacrylate polymerization by cerium(IV) (CAN)
primary alcohol in nitric acid under nitrogen, by the application of Tafts
correlation. It was suggested that the mechanism is free radical mechanism
(* =0, P= -0.2).
Kd
Ce(IV) + RCH2OH R-CH-OH+ Ce(III) + H
+ ----------19
In the polymerization of methyl methacrylate by Cerium(IV) [CAS]-
diol (propane 1, 2-diol16
and butane 1,4 diol17
) system in aqueous sulfuric
acid and under nitrogen, for the primary radical production step, complex
formation was not reported between cerium(IV)18
and diol.
In addition of kinetic results, the infrared spectrum of the isolated
polymers showed the presence of hydroxyl group along with those of the
homopolymer, indicating that the polymer contains the diol as an end-group
which envisages the initiation by primary radicals formed from the reaction of
Ceric ion with diol and termination by metal ions.
In the cases rate of polymerization was found to be directly proportional
to the concentration of diol and inversely proportional to the ceric ion
concentration but shows square dependence to the concentration of monomer.
The rate of ceric ion disappearance is directly proportional to the initial
concentration of ceric ion and diol.
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For the polymerization of methyl methacrylate with Cerium(IV) (CAS)-
glycerol ion aqueous sulfuric acid the termination step is postulated to mutual
at lower concentration of Ce(IV)0.5
where the rate of monomer disappearance
was found to be proportional to [Ce(IV)] and [Glycerol].
The termination step for the same system at high concentrations of
Ce(IV) termination step was proposed to be linear showing that the rate of
polymerization is proportional to [M]2[Glycerol].
The rate of ceric ion disappearance was found to decrease with increase
sulfuric acid concentration and increasing ionic strength by addition of
NaHSO4to constant sulfuric acid concentration.
Probably due to formation of neutral disulfate complexes of Ce(IV)
[Ce(SO4)2] according to following equilibrium.
Ce4+
+ HSO4
Ce(SO4)2+
+ H+
Ce(SO4)2+
+ HSO4
Ce(SO4)2+ H+
Ce(SO4)2+
+ HSO4
Ce(SO4)32
+ H+
In the polymerization methyl methacrylate (MMA) by Ce(IV) benzyl
alcohol [BA] system in nitric acid, the first order dependence of Rp on
(MMA) observed and the rate of Ce(IV) disappearance was proportional to first
powers of [Ce(IV)] and [BA]. The reaction of Ce(IV) benzyl alcohol
produces the free radical C6H5CH2OH which may partly be oxidized by
[Ce(IV)] to give benzaldehyde. The growing polymer chains get terminated by
the mutual annihilation of polymer radicals as evidenced by the dependence of
rate of polymerization over square roots of [Ce(IV)] and BA.
2.10 Dependence of polymerization rate on Initiator:
The polymerization rate to be dependent on the square root of the
initiator concentration. This dependence has been abundantly confirmed formany different monomer initiator concentrations over wide ranges of
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monomer and initiator concentrations. [East mond, 1976, a,b,c, : Kamatchi
et.a;., 1978 : Santee et.al., 1964; Schuez and Blaschke., 1942; V.Ranchan and
smets., 1959]19
The order of dependence of Rpon [I] may be observed to be less than
one-half at very high initiator concentrations.
The termination mode may change from the normal bimolecular
termination between propagating radicals to primary termination which
involves propagating radicals relating with primary radicals. [Perger et.al.,
1977; David et.al; 2001: Ito., 1980]20
.
Ktp
Mn
+ R
Mn-R ---------------21
This occurs if primary radicals are produces at too high a concentration
and / or in the presence of too low a monomer concentration to be completely
and rapidly scavenged by monomer.
If termination occurs exclusively by primary termination the
polymerization rate is given by
KpKi[M]2
RP= --------------------- ----------------22
Ktp
Lower than one-half order dependence of Rpon Ri is also expected if
one of the two primary radicals formed by initiator decomposition has low
reactivity for in initiation, but is still active in termination of propagating
radicals [Kaminsky et.al., 2002]21
2.11 Dependence of Polymerization Rate of Monomer :
The initiator rate can be monomer dependent in several ways. The
initiator efficiency may vary directly with the monomer concentration.
F = f [M]
Which would lead to firstorder dependence of Rion [M] and 3/2 order
dependence of Rpon [M], the equivalent result arises if the second step of the
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initiation reaction were to become the rate determining step. This occurs when
Kd> Kior when [M] is low.
The initiation reaction may be written as,
M + I M
+ R
And results in a 3/2 order dependence of Rp on [M]. This initiation is
probably best considered as an example of redox initiation.
2.12 Kinetics of Initiation and Polymerization :
The rate of producing primary radicals by thermal homolysis of an
initiator Rdand is given by
Rd = 2 fKd[I] -------------23
Where,
[I] is the concentration of initiators and f is the initiator efficiency. The
initiator efficiency is defined as the fraction of radicals produced in the
homolysis reaction that initiate polymer chains, the value of f is usually less
then unity due to wastage reactions, radicals that initiate polymer chains. The
value due to wastage reactions.
The normalizes of the initiator is the rate-determining step in the
initiation sequence, and the rate of initiation is then given by
Ri = 2 fKd[I] -------------24
Substitution of Eq 7 into Rp
fKd[I] 1/2
Rp = Kp[M] --------------------- ----------------25
Kt
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CHAPTER-II
3. REVIEW OF LITERATURE
Studies on kinetics of polymerization of methyl methacrylate initiate by
Ce(IV) redox systems are available in the literature. Some of them are as
follows.
C.M.Patra etal.,(1994)22
was investigated the influence of N-
acetylglycine on the kinetics of graft copolymerization of acrylonitrile (AN)
and methyl methacrylate (MMA) onto chemically modified jute fibers was
studied in the temperature range 40-600C. The optimum conditions for grafting
have been determined by the effects of concentrations of monomers, Ce(IV),
and N-acetylglycine on the rate of grafting. The effect of time, temperature, and
concentration of the acid, the amount of jute fibers and some organic solvents
and inorganic salts on the rate of grafting has been reported. On the basis of
experimental results findings out, a kinetic scheme has been proposed. Infrared
spectra of chemically modified jute and grafted jute have been investigated.
More than 185% graft yield could be achieved with the present system.
Grafting has improved the thermal stability of jute fibers.
M.Patra etal.,(1996)23
studying the polymerization of acrylonitrile
(AN) the Ce(IV) Citric Acid (CA) redox system as an initiator in aqueous
nitric acid solution, in the presence of an anionic surfactant, sodium dodecyl
sulfate (SDS) has been kinetically reported at a temperature range of 25-450C.
The rate of polymerization (Rp) and disappearance of Ce(IV) (-Rce) increase
with increasing concentration of SDS above its critical micelle concentration
(CMC) when the surfactant molecules are organized, Rp was found to be
proportional to [AN]1.5
and [CA]0.5
with other organic substrates Rp follows
the increasing order of sorbitol > mannitol > glycerol > CA. It was found to
decrease considerably in the presence of cationic surfaetant (CTAB), and
nonionic surfactant (Trition - X100) had no effect on the rate.Rce variouslinearly with [Ce(IV)] and [CA]. Both Rp and Rce increase with increasing
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temperature. The overall activation energy was found to be 18.31 and 13.72
k.cal mol in the absence and presence of 0.015 MSDS, respectively. The chain
length of the polyacrylonitrile has also increased with increasing SDS
concentration.
R.Chandragandhi etal.,(1997)24
was investigating the polymerizations,
of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in
aqueous nitric acid at 300C with the redox initiator system ammonium ceric
nitrateethyl cellulose (EC). A short induction period was observed as well as
the attainment of a limiting conversion for polymerization reactions. The
consumption of ceric ion was first order with respect to CE(IV) concentrationin the concentration range (0.20.4) x 10
-2M, and the points deviations from a
linear fit. The plots of the inverse of pseudo first order rate constant for ceric
ion consumption, (K1)-1
vs [EC]-1
gave straight lines for both the monomer
systems with non zero intercepts supporting complex formation between
Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)]
upto 0.003M, yielding an order of 0.41, then falls to 0.0055M and again shows
a rise at 0.00645M for MMA polymerization for AN polymerization Rp shows
a steep rise with [Ce(IV)] up to 0.001M and beyond this concentration Rp
shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the
presence of constant [NO3-] MMA and AN polymerization yield orders of 0.36
and 0.58 for [Ce(IV)] variation respectively. The rate of polymerization
increased with an increase in EC and monomer concentration, only at a higher
concentration of EC and [0.5M] was a steep fall in Rp observed for both
monomer systems. The orders with respect to EC and monomer for MMA
polymerization were 0.19 and 1.6 respectively. The orders with respect to EC
and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic
scheme involving oxidation of ECCe(IV) via complex formation, whose
decomposition gives rise to a primary radical initiation, propagation, and
termination of the polymeric radicals by biomolecular intervation the
polymeric radicals by biomolecular interaction is proposed. An oxidativetermination of primary radicals by Ce(IV) is also included.
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Novel block copolymers of poly (ethylene glycol) (PEG) with
various vinyl monomers namely acrylonitrile (AN), acrylamide (AAm), methyl
methacrylate(MMA) and methacrylic acid(MAA) were synthesized using Ce4+
-
PEG and Mn3+
-PEG redox system in aqueous acidic medium. The
polymerization proceeded via a macroradical generation, which was
substantiated by ESR spectroscopy. This macroradical acted as a redox
macroinitiator for the block copolymerization of vinyl monomers. The
formation of the block copolymers was confirmed by chemical test and
fractional precipitation, as well as by FT-IR,1H and
13C FT-NMR
spectroscopy. These polymerizations have been studied by S.Nagarajan etal.,
(1998)25.
C.Erbil etal.,(1998)26
was synthesized the polyacrylamides (PANMS)
polyacrylonitriles (PANS) and polymethyl methacrylates (PMMAS) by using
Ce(NH4)2 (NO3)6, Ce(SO4)2 4H2O and KMno4 in combination with
nitrilotriacetic acid (NTA) and diethylenetriamine penta acetic acid (DTPA)
which have strong chelating properties, as redox initiations, polymerizations,
were carried out in the aqueous acidic solutions at 250C and 550C in the
presence of air. The chain structures of the resulting products were studied by
fourier transform infrared (FTIR) spectroscopic measurements form the
comparison of the spectroscopic results with gravimetric and viscometric data
it was concluded that both the difference between he solubility behaviour in
aqueous solutions of MMA, AN, AAM, and their polymers and catalyst-
activator-monomer combinations were important parameters effecting the
polymerization mechanism, conversions and the structures of the polymers.
The FTIR and viscosity results indicated that PAAMS obtained in our
experimental conditions formed cross linked structures with sulphated
complexes of Ce (III) and Mnso4 produced by the redox reactions between
catalyst [Mno4
and Ce(IV)] NTA and AAM. The observed and PAN chains
were terminated by hydrated and sulphated complexes of Ce(III) while the
termination of PMMA radicals took place by primary radicals becausePMMAS were formed by emulsion polymerization kinetics.
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Nesrin Oz etal.,(2001)27
was investigating the Ethoxylated nonyl phenols,
ethoxylated fatty alcoholos, and ceric ammonium nitrate redox systems were
used for the polymerization of vinyl and acrylic monomers such as
acrylonitrile, styrene, and acrylic acid. The initiating radical was formed on
reducing organic compound which in turn initiated polymerization to give
polymers containing chain ends of ethoxylated nonyl phenols and ethoxylated
fatty alcohols that showed much higher water absorption. The effects of the
concentration of Ce4+
salt, ethoxylated nonyl phenols, and monomers on both
the yield and the molecular weight of corresponding polymers were studied.
V.S.Jamal Ahmed etal.,(2001)
28
studied the kinetics of radical freepolymerization of methyl methacrylate using potassium peroxomonosulfate as
initiator in the presence of benzyl tributylammonium chloride (BTBAC) as
phase transfer catalyst was studied. The polymerization reactions were carried
out under nitrogen atmosphere and unstirred conditions at a constant
temperature of 60oC in ethyl acetate /water bi-phase system. The rate of
concentrations of monomer, initiator, catalyst, temperature, acid and ionic
strength on the rate of polymerization (Rp) as certained. The orders with
respect to monomer, initiator and phase transfer catalyst were found to be 1.5,
0.5 and 0.5 respectively. The rate of polymerization (Rp) is independent of
ionic strength and PH.
Kavitha sankar etal.,(2002)29
investigated the kinetics and
mechanism of free radical polymerization of methyl methacrylate (MMA)
using water soluble initiator viz., potassium peroxydisulfate (PDS) in the
presence of newly synthesized 1,4-dihexadecylpyrazine-1,4-diium dibromide
as multi-site phase transfer catalyst(MPTC) has been investigated in ethyl
acetate/water two phase system at constant temperature 50+1oC under nitrogen
atmosphere. The effect of variation of [MMA],[PDS],[MPTC] ,and volume of
fraction of aqueous phase, solvent polarity and temperature on the rate of
polymerization (Rp) was ascertained. The order with respect to monomer,
initiator and multi-site phase transfer catalyst were found to be 1.0, 0.5 and 0.5
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respectively. The rate of polymerization of is independent of ionic strength and
PH.
A.K.Srivastava etal., (2003)30
investigated the homo polymerization of
methyl methacrylate(MMA) was carried out in the presence of triphenyl
stibonium 1,2,3,4- tetraphenyl- cyclopentadienylide as an initiator in dioxane at
65oC+0.1
oC. The system follows non-ideal radical kinetics (Rp [M]
1.4[I]
0.44)
due to primary radical termination as well as degradative chain-transfer
reaction. The overall activation energy and average value of Kp2/Ktwere 64 KJ
mol-1
and 0.173X10-3
/mol-1
S-1
respectively.
S.V.Subramanian etal.,(2004)31investigated the polymerization of
the monomer, methyl methacrylate (MMA) was carried out in sulfuric acid
medium at 15oC. With the redox initiator system, ceric ammonium sulfate-
malonic acid. There was no induction period, and a steady state was attained in
a short time. There was found to be no polymerization even after 1hr, in the
absence of the reducing agent R. The initiation was by the radical produced
from the Ce4+
-malonic acid reaction. The rate of monomer disappearance was
proportional to [M]1.5
, [R]0.5
and [Ce]0.3-0.5
, and the rate of ceric disappearance
was proportional to [R] and [Ce4+
]. Chain lengths of the polymers were directly
proportional to [M] and inversely to [R]1/2
and [Ce4+
]1/2
.
M.Dharmendira kumar etal.,(2004)32
studied the kinetics of free
radical polymerization of methyl methacrylate(MMA) using potassium
peroxydisulfafe as initiator in the presence of propiophenone benzyl
dimethylammonium chloride as phase transfer catalyst were studied. The
reactions were carried out under inert and unstirred conditions at constant
temperature of 60oC in cyclohexanone/water biphase media. The dependence
of the rate of polymerization on various experimental conditions, such as
different concentrations of monomer, initiator and phase transfer catalyst (PTC)
and different ionic strength, temperature and volume fraction of aqueous phase
was studied. The order with respect to monomer, initiator and phase transfercatalyst was found to be 1, 0.5 and 0.5 respectively. The rate of polymerization
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(Rp) is independent of ionic strength and PH. However, an increase in the
polarity of solvent and volume fraction of aqueous phase has slightly increased
the Rp value.Ye.S.Garina etal.,(2005)33
The kinetics of polymerization of methyl methacrylate initiated by
cerium (IV)-lactic acid redox system was studied in an aqueous medium in the
temperature range of 25-50oC. The rate of polymerization (Rp) and the rate of
Ce(IV) disappearance have been measured. The effects of some water-miscible
organic solvents, cationic, anionic, nonionic surfactants, and complexing
agents on the rate of polymerization were investigated. The temperature
dependence of the rate was studied, and the activation parameters werecomputed using the Arhenius and Eyring plots. The effects of inorganic and
organic solvents polymerization were also investigated by Mahadevaiah etal.,
(2006)34
.
The polymerization of methyl methacrylate initiated by the ceric
ammonium nitrateD-glucose redox system has been studied in aqueous nitric
acid under nitrogen in the temperature range 20.5 to 35oC.The initial rate of
polymerization was determined gravimetrically whereas the initial rate of ceric
ion disappearance was determined by titration of ceric ion. The relationships
between conversion and D-glucose, Ce(IV), and monomer concentrations were
determined. The dependence of the rates on D-glucose,
Ce(IV), and monomer concentrations was evaluated. The effect of temperature
was studied byM.D.Fernandez etal., (2007)35
.
M.D.Fernandez etal.,(2007)36
investigated the polymerization of
methyl methacrylate initiated by ceric ammonium nitrate-maltose has been
investigated in aqueous nitric acid under nitrogen in the temperature range
20.5-35Co.The dependence of the initial rate of polymerization and the initial
rate of ceric ion consumption on maltose, Ce(IV),and monomer concentrations
has been determined. The reaction orders were found to depend on ceric ion
concentration. At a moderately high Ce(IV) concentration (1X10
-3
mol litre
-1
)the orders were 1/2 and 3/2 with respect to maltose and monomer
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concentration, respectively and independent of Ce(IV) concentration. But a low
Ce(IV) concentration (4X10-4
mol litre-1
) the orders with respect to monomer
and Ce(IV) changed to 1 and 1/2 respectively.
Femeozturk etal.,(2007)37
was studying the comprehensive account on
the synthesis of block copolymers via redox initiating systems. Redox
polymerization systems for the synthesis of block copolymers have been
reported. The mechanism of initiation by a radox process is a method which is
used to obtain block copolymers by various transition metals, such as Ce(IV),
Mn(III), Cu(II), and Fe(III) redox polymerization has found wide applications
in initiating polymerization reactions in initiating polymerization reactions andhas been specifically of industrial importance. As it follows from the
Contents in addition to the above mentioned metals other redox
polymerization systems such as hydrogen peroxide and vanadium are described
as well.
The free radical terpolymerization of indene (In) methyl methacrylate
(MMA) and acrylonytrile (AN) has been investigated by Naguib, Hala.F
etal.,(2009)38
. The rate of polymerization of all the binary systems involved
dilatometrically for the homogeneous polymerization. The reactivity ratios of
the three binary systems were calculated and were found to be equal to 0.031
and 0.397 for In/AN copolymers and 0.02 and 3.82 for In/MMA copolymers
and finally 0.152 and 1.20 for AN/MMA copolymers. The rate of
terpolymerization in bulk has been measured as well as the relationship
between the monomer mixture composition and the obtained terpolymer in
order to construct the compositional triangle. Also the effect of initiator
concentration on the rate of terpolymerization was investigated.
Sunilkumar Banyal etal.,(2011)39
was studied the mulberry silk fibre
was graft copolymerized with binary mixtures of acrylic acid, methylacrylates
as the principal monomer in aqueous medium by using CAN as redox initiator.
The binary vinyl monomers were graft co polymerized by using the graftingconditions like reaction time, temperature, concentration of MMA and CAN as
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reported earlier for optimum percent grafting (74.40) of MMA alone onto the
same backbone. Graft copolymers were characterized by FTIR, SEM swelling
studies, moisture absorbance and chemical resistance in acidic and alkaline
medium. Dye uptake (Gention Violet) on graft copolymers were studied photo
calorimetrically at 420nm. The dying capabilities of the graft copolymers
with binary mixture is more that the reference graft copolymers of methyl
methacrylate.
P.L.Nayak etal.,(2011)40
was studying the grafting of acryonitrile onto
chitosan was studied using ceric ammonium nitrate as the redox initiation in
aqueous media. The percentage of grafting and the efficiency of the processwere calculated as function of the concentration of initiator and monomer the
reaction time and temperature. The percentage of grafting was found to depend
on the relative amount of monomer to chitosan, initiator and volume of the
aqueous phase as well as the reaction temperature. By using optimized
combinations of the reaction variables a grafting efficiency up 88% and a
percentage of grafting of nearly 20% were reached. Evidence of grafting was
obtained from comparison of SEM, XRP, and FTIR of the grafting and non-
grafted chitosan as well as solubility characteristics of the product. The
antibacterial and angifungal activities of the grafted polymer have also been
investigated.
M.Palanivelu etal., (2011)41
investigated the kinetics of polymerization
of methyl methacrylate initiated by Ce(IV)-Vanillin redox system in aqueous
solution of sulfuric acid at 40o
C. The rate of polymerization (Rp) and the
reaction orders with respect to monomer, initiator and ligand have been
determined and found to be 1.5, 0.5 and 0.5 respectively. The effect of
concentration of sulfuric acid on the polymerization was also studied. The rate
of polymerization was found to increase with increasing temperature 30-60o
C
and decreases at higher temperature (>600C). The overall activation energy
(Ea) was found to be 36.7 KJ/mol.
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4. SCOPE OF THE PRESENT WORK
Metal ions such as Cr6+
, V5+
, Fe3+
, Ce4+
, Co3+
, Mn3+
etc., coupled with
certain have been reported to be useful redox system for initiating vinyl
polymerization. For instance CE4+
have been found to be an active oxidant in
the vinyl polymerization, hence Ce4+
(Ceric ammonium sulphate) is chosen as
the oxidizing agent for the present investigation then also lactic acid
(CH3CHOHCOOH) reducing agent for the present work.
Detailed survey of literature reveals that an extensive study can be
carried out on methyl methacrylate, acrylamide, methyl acrylate, acrylic acid
and its derivatives with organic reducing agent like alcohols, aldehydes,
ketones, acids, amides, amines etc., which in combination with a oxidizing
agent constitute a redox pair to initiate the Vinyl polymerization.
Earlier, the redox polymerization of methyl methacryalate initiated by
various redox system has been investigated. Based on the kinetic studies of
polymerization of methyl methacrylate (MMA) initiated by ceric ammonium
sulphte (CAS) lactic acid (LA) redox system have been studied with a suitable
experimental methods. Hence the system is choosen for the present work.
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CHAPTER-III
5.EXPERIMENTAL PART
5.1 Polymerization Reaction Vessel
The reaction tubes used for the experiments were pyrex glass tubes
closed by B-24 cones in which nitrogen inlet and outlet tubes were fused. The
longer tube was used as inlet for puring nitrogen gas through the solution and
the shorter one was used as outlet for nitrogen. After passing nitrogen for the
specified time, the tubes were sealed with rubber gaskets to ensure maintenance
of an inert atmosphere.
5.2 Thermostat
The thermostat used was a rounded vessel with a heater, stirrer and
thermometer. The temperature range used for all the experiments reported were
300C and 35
0C controlled to an accuracy of 0.1
0C.
5.3 Deaeration Technique
The nitrogen gas used to deaerate the experimental system was free from
oxygen by passing through several columns of fisher solution. The gas after
passing through fisher solution was free from hydrogen sulphide, sulfur dioxide
etc, by passing it through a wash bottle containing saturated lead acetate
solution and then washed free of all vapours by passing it through a wash bottle
containing double distilled water. Before passing the purified nitrogen through
the reaction tube, it was passed through a wash bottle containing the same
concentration of monomer solution in order to avoid the loss of monomer
during deaeration. For all the experiments the deaeration time was 20 minutes.
5.4 Preparation of Fisher Solution
Fisher solution was prepared by dissolving 20g of sodium hydroxide in
100ml of water and adding 16g of sodium dithionate (N2S2O4) and 2g of
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anthroquinone sulphonate (silver salt) to the warm solution. The mixture
was stirred well until a clear blood red colour solution was obtained. It was
cooled of room temperature and then used. The fisher solution was changed for
every ten runs.
5.5 Reagents
All chemicals used were of the purest quality mostly BDH, E.Merck,
SDs fine (analar or G.R. Grade), SRL, products. Glasswares and the reaction
vessels were cleaned with warm solutions of chromic acid, rinsed frequently
with double distilled water and dried in air oven at 900C.
5.6 Water
Water was distilled in all glass cornery vessel, the second distillation
being from potassium permanganate and the double distilled water was used
throughout the study.
5.7 Monomer
CH3
Methyl Methacrylate [CH2 = C COOCH3] was recrystallised twice
from methanol and dried in vacuo.
5.8 Reducing Agent
The reducing Agent used in the present work is lactic acid
5.9 Acid
All experiments were conducted in sulphuric acid solution. Solution of
sulphuric acid were prepared by suitable dilution of concentrated acid with
double distilled water and standardized against sodium hydroxide solution.
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5.10 Purification of Reagents
To obtain reproducible results and to minimize experimental errors a
high degree of purity of the solvents and reagents were used. Therefore only a
analytical grade chemicals were used. Commercial sample and laboratory grade
reagents were carefully purified by standard procedure and then purity was
checked by melting point measurements.
5.2 Estimations
5.2.1 Initiator
Ceric ammonium sulphate was used as initiator. The Ce(IV) ion
concentration were determined by cerimetry. For this, an aliquot of Ce(IV)
stock solution was run into a known excess of standard ferrous ammonium
sulphate solution using ferroin indicator.
5.2.2 Ferroin Indicator
The ferroin indicator was prepared by dissolving 1.485g of 1,10-
phenantheroline monohydrate (C12H8N2H2O) in 100 ml of 0.025 ferrous
ammonium sulphate solution.
5.2.3 Rate of Polymerization (Rp)
The rate of polymerization (Rp) of methyl methacrylate was determined
by Iodimetry. The weight of polymer obtained in each experiment was
substituted in the equation given below to get Rp.
Rp = (1000 x W) / (V x T x M)
Where W = Weight of the polymer
T = Temperature
V = Total Volume of the reaction mixture.
M = Molecular weight of the monomer.
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R = Reaction time in seconds.
5.2.4 Rate of Ce(IV) Disappearance
Rate of Ce(IV) disappearance (-d[Ce(IV)]/dt) was determined asdescribed below. At the end of the reaction time, the reaction was arrested with
definite amount of ferrous ammonium sulphate on the excess ferrous ion was
determined by cerimetry. From the amount of unreacted ferrous ion, the Ce(IV)
consumed was evaluated and hence the rate of Ce (IV) disappearance was
computed.
5.2.5 Oxidation experiment
A typical oxidation experiment is described below. A reaction mixture
containing lactic acid, sulphuric acid, sodium bisulphate (to maintain the ionic
strength) and water (to maintain total volume constant) were taken in the
reaction tube. Nitrogen free from oxygen by passing through fisher solution by
bubbled through the solution for 20 minutes and the system was thermostated
at the desired temperature. The Ce(IV) stock solution was added and the tube
was sealed with rubber gaskets to ensure maintenance of an inert atmosphere.
The total volume of the reaction mixture was usually 20ml. At the end of the
reaction time (20 min), the reaction was arrested by the addition of a known
excess of ferrous ammonium sulphate solution, when the remaining Ce(IV)
was instantly reduced to Ce(III) state. The unreacted Fe(II) was estimated by
titrating with a standard ceric ammonium sulphate solution using ferroin
indicator. The rate of Ce(IV) disappearance was evaluated from the titre value.The rate of Ce(IV) disappearance was followed at different substrate
concentration, Ce(IV) concentration and sulphuric acid concentration keeping
the constant ionic strength.
5.2.6 Polymerization Experiment
In a typical kinetic run, a reaction mixture containing methyl
methacrylate, lactic acid, sulphuric acid, sodium bisulphate and water taken in
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the reaction tube was interposed between the nitrogen cylinder and the reaction
tube (to avoid loss of monomer during deaeration) nitrogen, free from oxygen
by passing through fisher solution, was bubbled through the solution for 20
minutes and the system was thermostated at the desired temperature. The
Ce(IV) stock solution was added and the tube was sealed with rubber gaskets to
ensure maintenance of an inert atmosphere. Polymerization started without any
induction period. At the end of the reaction time (20 min), the reaction tube
was opened and quenched with excess of ferrous ammonium sulphate
solution.The aliquot was done by iodimetry titration.From this titre value we
can determined the rate of polymerization (Rp)
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