A SYNTHESIS OF A NEW LIQUID CRYSTAL POLYESTER

A THESIS Presented to

The Academic Faculty

by

Takashi Namba

In Partial Fulfillment of the Requirements for the Degree

Master of Science in Polymers

Georgia Institute of Technology June 1992

I I

A SYNTHESIS OF A NEW LIQUID CRYSTAL POLYESTER

APPROVED:

Malcolm B. Polk, Chairman

Fred Cook

Satish Kumar

Date Approved by Chairman ^/^if^z

11

ACKNOWLEDGEMENTS

* I sincerely thank Dr. Malcolm B. Polk for his unending patience

and guidance during the course of this research. I also thank Dr. Fred

Cook and Dr. Satish Kumar for serving on my reading committee.

Secondly, I would like to show my special thanks to Nippon

Shokubai Co., Inc. for giving me an opportunity to study in the

Georgia Institute of Technology and supporting me during my

residence in the program for the M.S. in polymers.

I am also grateful to Mrs. Lynn Boyd, the director of the

Corporate Liaison Program, for helping me any time I faced

problems, even trivial ones.

Finally, I thank my wife, Yuka, and my son, Kazuyuki, for

supporting me physically and mentally. I believe I could not have

finished my master's work if they had not been with me.

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT i i i

LIST OF TABLES v i

LIST OF FIGURES v i i

SUMIVIARY X

CHAPTER

I. INTRODUCTION AND BACKGROUND 1

History and Definition of Liquid Crystals Classes of Liquid Crystals Classes of Order Structures, Pathways, and Properties of LCP's Method of Mesophase Identification

Differential Scanning Calorimetry and Differential Thermal Analysis Miscibility Studies X-ray Diffraction Polarized Optical Microscopy

Objectives

II. EXPERIMENTAL DETAILS 32

Measurements and Instrumentation Chemicals Synthesis of Poly[oxy(2-acetyl-1,4-phenylene)-oxy-terephthaloyl-co-oxy(2-acetyl-1,4-phenylene)oxyisophthaloyl]

Asymmetric Reduction of Poly[oxy(2-acetyl-1,4-phenylene)oxyterephthaloyl-co-oxy(2-acetyl-1,4-phenylene)oxyisophthaloyl]

III. RESULTS AND DISCUSSION 3 9

General Comments on Synthetic Method Solubility Dilute Solution Viscosity Spectroscopic Analysis

Fourier Transform Infrared Spectroscopy Proton Nuclear Magnetic Resonance Spectroscopy Carbon-13 Nuclear Magnetic Resonance Spectroscopy Conclusions From Spectroscopic Analysis

Thermal Analyses Differential Scanning Calorimetry Thermogravimetric Analysis

IV. CONCLUSIONS AND RECOMMENDATIONS 5 7

APPENDIX 63

REFERENCES 66

V

LIST OF TABLES

Tabig PaqQ

1. Structures of Commercial Thermotropic Liquid Crystalline Polymers 3

2. Monomers Used in the Synthesis of Liquid Crystal Polyesters 1 4

3. Absorption Peaks and Assignments for the Polymer Before the Reduction 4 2

4. Absorption Peaks and Assignments for the Polymer After the Reduction 4 5

V

LIST OF FIGURES

Figure Page

1. The Viscosity Behavior of the PPTA-Sulfuric Acid System 5

2. Schematic Representation of the Different Types of Mesophases 8

3. Schematic Representation of the Structures of Liquid Crystal Polymers 1 0

4. Schematic Diagram of the Structure of a Main-chain Liquid Crystal Polymer 1 3

5. Methods to Lower Melting Point 1 5

6. Melting Point vs. Structure 1 7

7. Schemes for Syntheses of Side-chain Liquid Crystal Polymers 1 8

8. Examples of the Applications of Main-chain Liquid Crystal Polymers 2 0

9. Thermal Behavior of Liquid Crystal Polymers 2 3

10. X-ray Diffraction Patterns for Unoriented (a) Nematic and (b) Smectic Phases 27

11. Textures of Liquid Crystals in POM 2 9

12. Synthesis of Poly[oxy(2-acetyl-1,4-phenylene)oxyterephthaloyl-co-oxy(2-acetyl-1 ,4-phenylene)oxyisophthaloyl] 35

V

Figure Page

13. Asymmetric Reduction of Poly[oxy(2-acetyl-1,4-phenylene)oxyterephthaloyl-co-oxy(2-acetyl-1,4-phenylene)oxyisophthaloyl] 37

14. FTIR Spectrum of the Polymer Before the Reduction 41

15. FTIR Spectrum of the Polymer After the Reduction 4 4

16. Proton NMR Spectrum of the Polymer Before the Reduction 4 6

17. Proton NMR Spectrum of the Polymer After the Reduction 4 7

18. Carbon-13 NMR Spectrum of the Polymer Before the Reduction 4 9

19. Carbon-13 NMR Spectrum of the Polymer After the Reduction 50

20. Differential Scanning Calohmetry Thermogram of the Polymer Before the Reduction 5 2

21. Thermogravimetric Analysis Thermogram of the Polymer Before the Reduction 53

22. Differential Scanning Calorimetry Thermogram of the Polymer After the Reduction 55

23. Thermogravimetric Analysis Thermogram of the Polymer After the Reduction 56

24-1. Scheme for the Organic Synthetic Route 6 0

24-2. Scheme for the Organic Synthetic Route 61

IX

Figure Page

25. Proton NMR Spectrum of valinol 64

V'^' 26. Carbon-13 NMR Spectrum of valinol 6 5

SUMMARY

The importance of main-chain liquid crystal polymers(LCP's)

as structural materials is continuously increasing. Generally

speaking, there are currently two major interests in main-chain LCP

research. The first is the reduction of the cost in LCP manufacture,

and the second is the improvement of their mechanical or thermal

properties.

In order to improve the mechanical properties, LCP's should

have as highly rigid and linear a structure as possible. However, an

LCP which has a more rigid structure is more difficult to process

since it has a higher softening temperature. Thus, thermotropic

LCP's in the current market are usually co-polymerized with rigid

monomers (sometimes with less rigid monomers) in order to reduce

the rigidity or linearity of the structures and in order to depress the

processing temperature. Another drawback of current LCP's is their

poor transverse mechanical properties compared to their mechanical

properties along the molecular direction. This problem is the result

of their highly oriented structure in only one direction. Currently,

the solution to this problem is glass fiber filling. Glass fibers are

dispersed in LCP's randomly to relieve the anisotropy of LCP's.

However, these fibers also increase the density of composites, and

this would be a problem when they are used for an application in

which the density of the material is the main concern. Another

possible solution to the poor transverse properties is the change or

modification of the mesophase of LCP's from nematic/smectic to

cholesteric, and this may be accomplished by introducing a chiral

center in their structure.

In this thesis, a new main-chain LCP, poly[oxy(2-acetyl-1,4-

phenylene)oxyterephthaloyl-co-oxy(2-acetyl-1 ,4-phenylene)oxyiso-

phthaloyl] was synthesized by applying a method described by

Onwunaka. An asymmetric reduction was also performed on

poly[oxy(2-acetyl-1,4-phenylene)oxyterephthaloyl-co-oxy(2-acetyl-

1,4-phenylene)oxyisophthaloyl]. The structure of the polymer before

reduction was confirmed by nuclear magnetic resonance

spectroscopy (NMR) and Fourier transform infrared spectroscopy

(FTIR). The reduction of poly[oxy(2-acetyl-1,4-phenylene)oxytere-

phthaloyl-co-oxy(2-acetyl-1,4-phenylene)oxyiso-phthaloyl] was

successful since the disappearance of the keto carbonyl carbon was

confirmed by FTIR and carbon-13 NMR. However, the structure of the

polymer after reduction could not be determined by those

spectroscopic techniques because the polymer contained (s)-(+)-2-

amino-3-methyl-butan-1-ol as an impurity which was not

separated. The inherent viscosity of the polymer after reduction

was 0.11 dL/g which was much less than that of the polymer before

reduction (0.42 dL/g).

CHAPTER I

^^ INTRODUCTION

Historv and Definition of Liquid Crystals

Liquid crystal behavior was discovered by F. Reinitzer during

his study of cholesteryl benzoate in ISSSJ He noticed that this

material changes from the solid crystalline state to the turbid

anisotropic liquid at 149°C, and becomes a transparent isotropic

liquid at 179°C. Materials which have such a behavior as cholesteryl

benzoate were successively called "flowing crystals" or "crystalline

liquids" until O. Z. Lehmann et al. called them "liquid crystals."2

Almost fifty years after the discovery of low molar mass

liquid crystals, F. C. Bawden et al. reported the first polymeric

liquid crystal.3 They observed that a solution of tobacco mosaic

virus formed two phases, one of which was birefringent, above a

critical concentration. After this, other basic studies on polymeric

liquid crystals were done by A. Elliot et al.'^ and C. Robinson et al.^

in the 1950's. Even after those pioneering workers investigated

polymeric liquid crystals, it took twenty more years before

polymeric liquid crystals were recognized as important structural

materials.

In the 1970's, E. I. DuPont de Nemours and Co. developed and

commercial ized high-strength f ibers (Kevlar®) from po ly (p-

phenylene terephthalamide)(PPTA).6

" _ / =

- " - \ J n

This was the first commercialized LCP product, and it has led to

numerous developments in both new materials and applications, as

well as in the underlying science. Although Kevlar® has

extraordinarily high strength, it can be processed from only special

solutions and is not melt processible because its melting point is so

high that it degrades before melting.

Following the invention of Kevlar®, the first melt processible

LCP was reported by W. J. Jackson et al .^ , and commercialized

immediately by Dart Industries and other U. S. and European

companies. Table 1 shows structures of common thermotropic LCP's

commercially available with the brand name and the suppliers.

The liquid crystalline state has been defined in several

different ways. In the chemical dictionary, it is defined as an

intermediate or mesomorphic ("middle" phase) state between solid

and liquid.8 From this definition, the liquid crystalline phase is

sometimes referred to as a mesophase. Blumstein states that the

Table 1. Structures of Commercial Themotropic Liquid Crystalline Polymers

1. X7G (Eastman Kodak), Novaculate (Mitsubishi Kasei), Rodmn (Unitika), Idemitsu LCP (Idemitsu Petro Chem.)

V / C-O—CHsCHsO-

n \ //

-im

2. Xydar (Amoco), Econol (Sumitomo Chemical)

- - 0 \ / ^ /r\ //

0 ^

H 3. Vectra (Hoechst-Celanese, Polyplastics)

" ^ / °<^i

liquid crystalline state is a state of matter which simultaneously

has certain properties of a liquid and certain properties of a

crystal.9 Still another definition is available in which the liquid

crystalline state is described as a melt or solution which shows

some type of anisotropic order in the fluid state. This final

definition is probably most important because it clearly

distinguishes the liquid crystalline state either from both isotropic

melts and solutions and crystals which have three dimensional

order.

Classes of Liquid Crystals

Liquid crystals can be broadly classified into two groups:

lyotropic and thermotropic^'IO"''"^

Lyotropic liquid crystals are materials which show liquid

crystallinity in solutions above the critical concentration and in a

particular temperature range, and most LCP's investigated in early

researches like PPTA are classified as lyotropic liquid crystals. Fig.

1 shows the schematic relationships between the viscosity of the

solution and the concentration or temperature in the PPTA-sulfuric

acid solution system. The viscosity increases rapidly until a

critical concentration is reached. At the critical concentration, the

number of molecules in the solution is so high that the molecules

begin to align in order to remain in the solution and the lyotropic

V) o u

>

Concentration

Temperature

Fig. 1. The Viscosity Behavior of PPTA-Sulfuric Acid System

mesophase is formed. Above the critical concentration, the

viscosity decreases sharply by the formation of the lyotropic

mesophase up to a particular concentration. In this region, the

solution is a mixture of the isotropic liquid phase and the lyotropic

mesophase. As the concentration increases further, the solution

becomes fully lyotropic, and the viscosity increases again.

Lyotropic LCP's do not usually show LC behavior in bulk, primarily

because their melting points are generally so high that they degrade

before they melt.

Thermotropic liquid crystals are materials which show liquid

crystallinity when they melt. Thermotropic LC's are classified into

two subclasses, enantiotropic and monotropic. In enantiotropic LC's,

the LC state is thermodynamically stable and is observed both upon

heating from a solid phase and upon supercooling from an isotropic

liquid phase to below the clearing temperature. In monotropic LC's,

on the other hand, the LC state is metastable with respect to the

solid, and is observed only upon supercooling.

Classes of Order

The liquid crystalline state is characterized by long range

orientationally ordered mesogens which are responsible for the

liquid crystallinity of molecules. LC phases are classified into four

classes by their degree of order. The schematic images of these

four phases are shown in Fig. 2.^^ The ovals In the figure represent

the mesogens.

The first class of LC phases is called the smectic state. This

is the most ordered state of all of the four phases. In this state, the

mesogens are arranged in ordered (Fig. 2(a)) or unordered (Fig. 2(a'))

layers, and their centers of gravity are mobile in two dimensions (in

the smectic plane). Smectic phases are further classified with

respect both to the order of the arrangement of the mesogens in each

smectic plane and to the angle, called the tilt angle, made between

the long axes of the mesogens and the plane. For example, smectic A

(SA) is characterized by no order in mesogen arrangement in the

smectic plane and 0° in the tilt angle, and smectic C (Sc) is

characterized by no order in mesogen arrangement in the plane like

SA and non 0° in the tilt angle. In the case of low molar mass LC's,

11 smectic states from smectic A (SA) to smectic K(SK) have been

discovered''3 ^ but in the case of LCP's, only a few smectic states

have been observed.

Normal SA SB SE

Tilted SC S I—SF —SJ—SG—SH—SK

The order of the phases increases from left to right and lines

indicate which transitions can occur upon heating or cooling.

a'

y IV W Y

Fig. 2. Schematic Representation of the Different

Types of Mesophases. Smectic with ordered

(a) and unordered (a') arrangement of the molecules

in layers; b) nematic; c) cholesteric; and d)

discotic. " 2

The second phase, called the nematic state, is characterized by

the orientation of the long axes of mesogens along a certain

direction with an unordered arrangement of centers of gravity of

the mesogens (Fig. 2(b)). Generally speaking, the materials in the

nematic phase have lower viscosity than those in the smectic phase

since the nematic state allows for translational mobility of

constituent mesogens.

The third phase is called the cholesteric state. This phase is

formed by derivatives of cholesterol or optically active chiral

nematic LC's. The cholesteric state is characterized by the

mesogens assembled in layers, a similar arrangement to that in the

nematic phase, but each layer is rotated by a certain angle with

respect to the preceding layer so that some helical twisting of the

mesogens occurs on the whole, describing a helix with pitch p (Fig.

2(c)).

The last LC phase is called the discotic phase. This phase

consists of plate-like mesogens, instead of rod-like mesogens as in

the other three phases. The mesogens lie in the plane of the layers,

forming close hexagonal packings (Fig. 2(d)).

Structures. Pathways, and Properties of LCP's

Fig. 3 shows the schematic representation of the structures of

LCP's. The structures of LCP's are generally classified into three

10

1 • Main Chain LCP's

(a)

(b)

J ] ] I

] I I r (c)

(d)

2_Side_CliainJ_CE!s

3. 1. and 2. mmhinficl

s^—

Fig. 3. Schematic Representation of the Sturctures of LCP's

11

groups: main chain LCP's, side chain LCP's, and the type in which both

main chain and side chain are combined.

In main chain LCP's, mesogenic groups are incorporated into

the polymer backbone. Main chain LCP's are further classified into

four types. The first type is the all-rigid LCP, in which the polymer

backbone consists of only the mesogenic group. The second type is

the semi-rigid LCP's in which mesogenic groups are connected by

some soft segment like an alkylene group. The third type is

characterized by soft branches on the mesogenic groups. The last

type consists of mesogenic groups with more than two

functionalities. These mesogenic groups are connected to each other

with/without soft segments and have soft branches.

In side chain LCP's, the mesogen is hung like a pendant on the

polymer backbone through a short or long flexible spacer. The spacer

preserves the delicate interactions between pendant mesogens by

decoupling the main chain motion from that of the pendant group.

The last type of LCP has a structure which has both main chain

and side chain LCP features.

The factors required to make a polymer have LC behavior are

basically similar to those for low molecular weight LC's suggested

by Gray et al.14 ,

1. Mesogenic groups should have rod-like or disk-like

structures.

12

2. Mesogenic groups should have sufficient permanent dipoles

to stabilize the liquid crystalline state.

Fig. 4 shows the most common structures exhibiting LC

behavior and a variety of chemical structural units that are

available for the synthesis of main chain LCP's.15-16 Most main-

chain LCP's are synthesized through condensation polymerization,

and several kinds of monomers commonly used for thermotropic

LCP's are listed in Table 2.''^ Although the combinations of these

monomers give all rigid (all aromatic) liquid crystal polymers, they

are often not melt processible because of their extremely high

melting points.

In order to lower the melting point of LCP's, several

techniques to interrupt the crystalline order are available, as

summarized in Fig. 5.18

1. Copolymerization of several mesogenic monomers such

as p-hydroxy-benzoic acid (PHB) or 2-hydroxy-6-

naphthoic acid produces random copolymeric structures

with depressed melting points.

2. Use of monomers with bulky side groups, such as

phenylhydroquinone, prevents close packing in the

polymer crystals.

1 3

B Lateral substituent on aromatic

rings such as CI, Br, CH3,

OCH3, phenyl, n-alkyl

Various types 0 f end groups

-OR -R -COOR - C O R

-OOCR - O O C O / i CH coo;i - C N - C I - N O 7 - H - F - B r - J -R' - N = C = 0 - O i l -OR' -OCOR' - N H , -COOR' -CR=CR-COOR -SR - N H / ?

- N H C P f i - N K , - N = C = S

- 0 ( C H j ) „ O f t - O C F 3

D

A Various types of r i g i d core

and r i n g systems

• ^ 0 ^ - ^ ^ ^ {{ 34 K^ -Qi] ®-

^0^ X CI, Dr. \, on, OR, OOCR R is C„H,„.,

CHj. CN. NO,

-^Q:P—^^

- ^

N;=^ N - N

-<Q—0- -13-N - N

-<o>-oy OI J^ N-N

C Various types c >f b r i d g i n g groups

J^ ^C^^ i

0

- c = c -CH

H

r~ H 0 0

CM CU Cll ctr'^N-™-

-Hg— —N=C=N— - ( C H , ) , -

d Si^ N

CH, CH,

-NH(CH,),- -0(CH,)„O-

-COO(CH,)„OOC— —(CH,),COO —

Fig. 4. Schematic Diagram of the Structure of a Main

Chain Liquid Crystal Polymer 15-16

1 4

Table 2. Monomers Used in the Synthesis of Liquid Crystal

Polyesters ^^

Aromatic diol Aromatic dicarboxylic acid Hydroxyacid

MO-

X \

-OH

MO-

Y

-OH

O O

HOC—{(J\-COH

O O

HOC-/Q/-<^OH

H0--(j3Vc0H

X

0 11 COH

(X, Y - halogen or alkyl) (X » halogen, alkyl) (X - halogen, alkyl)

MO, O

oTo OH

<oc-/Q V-/O/-COM

H 0 - < 0 } - { 0 ) - 0 H o H

HOC

HO—( ( ) > - 0 H oTo

COM II

o O

MO.

^ ^ ^ ^ COH

HO-('Q\-CH=CHCOH

oc ^ Cj \-o^ (^ V-c oi!

(X = H, halogen, alkyl)

1 !>

1) Copolymerization

H0-< O >-C-OH HO

0 II C-OH

2) Bulky Side Group

3) Bent Comonomer

HoYoVoH

R=CH3. C I , H

0 0 1 I

»0^,,^^W H O C . ^ - \ COH HO-rOrCOH

Ol ' TOT ' lO HO-/c\o !2^°"

4) FTexible Spacer

4CH2)-n ; 40-CH2-CH2>„

CH

; -(O-Sih I ' CH

Fig. 5. Methods to Lower Melting Point ^^

16

3. Use of bent comonomers which contain the 1,3-

disubstituted phenylene structure, such as isophthalic

acid, (which are not inherently liquid crystalline

precursors) interrupts crystalline order.

4. Flexible spaces, such as alkylene groups, decrease

polymer rigidity. Polymers with the mesogenic groups in

the side chain are included in this class.

The effects of these melting point depressing technique are also

shown in Fig. 6.

Side chain LCP's are usually synthesized through radical

polymerization. There are two radical synthetic routes to introduce

mesogenic groups in a polymer.''^ Those routes are shown in Fig. 7.

In scheme I, the mesogenic group is attached to the monomer before

polymerization. In scheme II, on the other hand, the mesogenic

groups are attached after the backbone polymer is synthesized.

Scheme I is more common because it is easier to synthesize a side-

chain LCP and introduces mesogenic group more completely.

LCP's have several superior properties over conventional

plastics. Almost all features of LCP's are caused by the combination

of the polymer specific properties such as the ease of processing

and the anisotropic properties of the liquid crystalline state.'' ^

Positive and negative features of main chain LCP's are listed below.

I /

Bulky Side Group T (Melting) °C

u w

> 600

-c-ZoVc-o/oVo-

o

340

Bent Monomer

0 0 0

(o<o>o)(?<o>!|(E O O i l 0.5

T (Mel t ing) °C

400

°<o>!)("<o>')(2 0.5

" "oTo--' )('1ojk = 350

Flexible Group

0 0

- C - < ^ O ) ^ C - O H ( ^ O -

T (Melt ing) °C

> 400

r - c / o Vo-(CH^)^-o/o\c-o-/o\o- 210

CH.

Fig. 6. Melting Points vs. Structure 18

-^ - .J .— M.

ScbemeJ

18

Attaching

Mesogens

Polymerization

SchemeJl

Polymerize

Attaching mesogens

Fig. 7. Schemes for Side-chain Liquid Crystalline Polymers

19

Positive

(1) Exceptionally high mechanical properties (high

modulus, high strength, good wear resistance,

etc.)

(2) High dimensional stability (thermal expansion

coefficients are as low as 2 x 10-^ °C-'')

(3) High thermal stability

(4) High chemical stability

(5) Lower density compared with that of metals

Negative

(1) High cost

(2) Poor properties transverse to the machine

direction

(3) Weak weld lines

Fig. 8 shows some examples of the applications of main chain

LCP's .

The applications of side-chain LCP's are still under

investigation. However, the high mobility of mesogens in side-chain

LCP's gives quick response as fast as low molar mass LC's to

external stimuli, and side-chain LCP's have great potential as

optical memory storage, and holographic imaging, or nonlinear

optics.

20

Fig. 8. Examples of the Applications of Main-chain LCP's 1) connectors, coil bobbins, and gears; 2) coil bobbins; 3) speakers; 4) surface mount connectors; 5) multifilament yarns; 6) plastic storage containers

21

Methods of Mesophase Identification

There are several techniques for lower mass LC's to verify

that a mesophase exists and to classify it as nematic, cholesteric,

or smectic A-K. Noel lists some of these developments as the

following:20

(1) Differential scanning calorimetry (DSC) or differential

thermal analysis (DTA) to examine enthalpy changes.

(2) Miscibility studies to compare the behavior of unknown

liquid crystal phases with those of known origin.

(3) X-ray diffraction to study differences in molecular order.

(4) Polarized light microscopy to examine textures and

optical patterns.

In the case of LCP's, a combination of these methods is often

necessary to identify the mesophase types because of their broad

molecular weight distributions, high viscosities, and features as

mixtures of polycrystalline and amorphous material.21

An additional complication for polymer systems is that more

than one type of mesophase may be present, depending on the

22

temperature. Such materials, which are termed polymorphic,

complicate the identification procedure.22

Differential Scanning Calorimetrv (DSC) and Differential Thermal

Analysis fPTA)

DSC and DTA are popular and convenient methods for

determining the thermal behavior of materials. Transition

temperatures and transition enthalpies are easily measured by these

methods, and transition entropies can be conveniently calculated.

Fig. 9 shows a typical DSC scan of thermotropic LCP's with

descriptions of the transitions and interpretations of the structural

arrangements in the different phases.23 Below the glass transition

temperature (Tg), no long range molecular motion is allowed and the

material behaves like semicrystalline plastics. At Tg, the

amorphous region starts to undergo liquid-like motions and the slope

of the curve suddenly changes. Above Tg, the amorphous region

becomes liquid-like, but the crystalline region maintain the

structure. In some LCP's, the transition at TKI-K2 is observed

indicating a crystal lattice change. At the melting point (Tm), the

crystalline region undergoes melting and three-dimensional order is

lost. Above Tm, the system becomes a fluid, but continues to have a

loose, two-dimensional order which can be characterized as a

smectic phase (LCi). As the temperatureincreases, more order is

-^- INCREASING TEMPERATURE

MOLECULAR

ARRANGEMENT

TRANSITION:

FROM:

TO:

TKI K2 TM - ''"K2 LCI

Glass/Crystalline Crystalline-1 Cry3talline-2

Crystalline-1

TLC1-LC2 TIJC2-I

Liquid Crystal-l Liquid Crystalline Melt-2

Cry3talline-2 Liquid Crystal-l Liquid Crystal-2 Isotropic Melt (i.e., Smectic) (i.e., Nematic)

Fig. 9. Thermal Behavior of Liquid Crystal Polymers 23

24

increases, more order is lost and the other transitions to less

ordered liquid crystalline phases, i.e., the nematic state, can

sometimes be observed before the final transition temperature is

reached. At the last transition temperature, all liquid crystalline

order is lost, and the system finally becomes an isotropic fluid.

This temperature is often referred to as the clearing temperature.24

Since only two transitions, the glass transition at Tg and melting at

Tm, are observed in the case of conventional semicrystalline

plastics, the multiple transitions are clear evidence of the

existence of liquid crystallinity.

DSC and DTA not only reveal information about the transition

temperature, but sometimes make it possible to classify liquid

crystalline phases from their enthalpy data. Krigbaum states rough

guidelines about the isotropization enthalpies for nematics (0.30 -

0.85 kcal/mol of repeating unit) and smectics (1.5 - 5.0 kcal/mol of

repeating unit).'' ^

Miscibilitv Studies

Mutual miscibility is the method developed by Sackmann and

Demus according to the rule of selective miscibility.25 in this

method, a liquid crystal whose mesophase is unknown is mixed with

a reference liquid crystal whose mesophase is known. If the mixture

shows liquid crystallinity at any composition, the unknown and the

25

reference have the same type of the mesophase. However, the

converse is not necessarily true^O , and in this case, further

analysis by a different technique is required. Mutual miscibility has

been successfully applied to nematic26-27 ^ smectic A 2 8 and

smectic C^^ phases.

For the quick determination of mesophases by mutual

miscibility, the contact method can be conveniently used.29 In this

method, a small amount of the unknown liquid crystal in the

isotropic state is placed between a glass slide and a cover slip.

Then the reference liquid crystal is introduced from one end of the

cover slip by capillary flow. As the reference liquid crystal

diffuses into the unknown liquid crystal, a continuous composition

gradient is produced from one end to the other. After cooling, the

sample is examined under a polarizing microscope equipped with a

heating stage in order to observe the miscibility.

X-rav Diffraction

X-ray diffraction gives information about the arrangement and

mode of the packing of molecules and the types of order present in

the mesophase."13 X-ray diffraction studies can be performed using

either unoriented or oriented samples. Unoriented samples are

easier to prepare, but oriented samples are more informative for

structural analysis. Oriented liquid crystalline samples can be

26

prepared either by cooling them in a strong magnetic field from the

isotropic melt to the mesophase or by melting a single crystal or an

oriented fiber very carefully.

Fig. 10 shows X-ray diffraction patterns of the unoriented

nematic phase and the unoriented smectic phase.

A diffractogram of the unoriented nematic mesophase is

characterized by a weak, diffuse outer ring and a strong diffuse

inner ring.30 The outer ring and the inner ring indicate the average

distance between neighboring molecules and the length of the unit

cell, respectively. The diffuse rings indicate that only short range

positional order exists in the nematic phase. Cholesterics give very

similar diffraction patterns to these of the nematic phase. If the

nematic phase is oriented, splitting of those two rings is observed.

The diffractogram of unoriented smectic A or C mesophases is

characterized by one or more sharp inner reflections and a diffuse

outer ring. The sharper inner reflections indicate smectic layering

and the diffuse outer ring shows short range order within the layers.

In the case of oriented SA or Sc samples, the inner rings degenerate

to reflections which lie along the meridian, but the outer ring shows

different reflections between SA and Sc mesophases. For SA, the

outer reflection degenerates to a broad ark-like reflection lying on

the equator. For Sc, the outer reflection splits into doublets

positioned around the equator.

A diffractogram of the smectic B mesophase is characterized

by sharp inner and outer reflections. These sharp reflections are due

L /

(a)

(b)

Fig. 10. X-ray Diffraction Patterns for Unoriented (a)

Nematic and (b) Snnectic Phases 30

28

to the higher ordered mesophase characteristic of SB in which

smectic layers are no longer two dimensional fluids but seem to be

two dimensional solids.

The other smectic mesophases are less strongly characterized

with respect to their molecular structure.

Polarizing Optical Microscopy

Polarizing optical microscopy (POM) is a very useful technique

for a preliminary characterization of the mesophases. In POM, a

picture of a thin layer of a liquid crystal is observed by means of a

microscope usually in linearly polarized light. The features of the

picture, termed "texture" by Friede|31-32 ^ are caused by the

existence of different kinds of defects, and mesophases (nematic,

smectic, and cholesteric) are identified based on this postulate.

Several textures observed in POM are shown in Fig. 11.

Nematic LCP's generally show a threaded texture or a schlieren

texture. Semi-rigid and side-chain nematic LCP's usually show

similar textures to lower mass LC's, but not all aromatic LC

polyesters show these typical textures.

Smectic LCP's show several kinds of textures: schlieren, fan-

shaped batonnets, and mosaic, etc. The schlieren texture is observed

both in the smectic phase and in the nematic phase, but in the case

of nematic LCP's, the image can be brightened by applying shear to

29

30

the sample placed between two glass plates. This is caused by the

lower viscosity of nematic LCP's compared with that of smectic

LCP's.

Cholesteric LCP's also show several kinds of textures: fan-

shaped, planer, and Grandjean textures, etc. In order to identify a

mesophase which shows a fan-shaped texture, the sample is placed

between two glass plates and then one of the glass plates is shifted

after the fan-shaped texture is observed. The mesophase is

identified as smectic if the texture remains fan-shaped. It is

identified as cholesteric if the texture changes to a planar or

Grandjean texture.

ObiQCtivg?

There were two main objectives to this research. The first

one was to synthesize the nematic liquid crystalline copolymer,

poly[oxy(2-acetyl-1,4-phenylene)oxyterephthaloyl-co-oxy(2-acetyl-

1,4-phenylene)oxyisophthaloyl], by applying the procedure

established by Onwunaka^^ Since a homogeneous system is

preferred to accomplish the reduction, the polymer being reduced

should be soluble in a solvent which will not destroy the reducing

system. Unfortunately, the nematic liquid crystalline homopolymer,

poly[oxy(2-acetyl-1,4-phenylene)oxyterephthaloyl], synthesized by

Onwunaka was only partially soluble in solvents suitable for

31

reduction, e.g. 1,1,2,2-tetrachloroethane or chloroform. Thus, in

this research, a third monomer, isophthaloyi dichloride, was used to

make the polymer structure less linear, to loosen the packing of

molecules, and consequently to enhance the solubility of the polymer

in those solvents.

The second objective of this research was to produce a

cholesteric liquid crystalline polymer through asymmetric

reduction. It was believed that the introduction of optically active

groups would change the starting nematic liquid crystalline polymer

to a cholesteric one. In consideration of safety, cleanliness, and

high optical yield of the reducing system as discussed by Haley34^

the borane/aminoalcohol reducing system developed by Itsuno et

al.35 was adopted for this research.

The goal of this project is the synthesis of a cholesteric liquid

crystalline polymer in order to improve nematic liquid crystalline

polymers' poor transverse mechanical properties, which are the

result of the high molecular orientation of nematic liquid

crystalline polymers in only one direction. Since the molecular

direction of cholesteric liquid crystalline polymers is twisted plane

by plane, uniform mechanical properties in all directions would be

expected.

32

CHAPTER II

EXPERIMENTAL DETAILS

Measurements and Instrumentation

Intrinsic viscosities were measured at 30°C with an Ubbelohde

type viscometer in 2-chlorophenol.

Proton NMR spectra and carbon-13 NMR spectra were obtained

with a Varian XL-400 NMR. All of the NMR spectra were obtained on

polymer solutions in trifluoroacetic acid. Fourier Transform

infrared (FTIR) spectra were obtained with a Perkin Elmer 1600

Series FTIR spectrometer and all samples were prepared as

potassium bromide pellets.

Differential scanning calorimetry (DSC) was performed on a

Seiko Instruments DSC 220C under nitrogen atmosphere. All of the

DSC scans were baseline corrected. A temperature range of -50°C to

300°C was used in each scan with a scan rate of 20°C per minute.

Thermogravimetric analysis (TGA) was performed on a Perkin Elmer

TGA 7 Series under nitrogen atmosphere. A temperature range of

50°C to 500°C was used in each scan with a scan rate of 20°C per

minute.

33

Chemicals

TerephthaloyI chloride and isophthaloyi dichloride obtained

from Aldrich Chemical Company, Inc. were recrystallized from

hexane. 2',5'-Dihydroxyacetophenone obtained from Aldrich Chemical

Company, Inc. was also recrystallized from a 3:1 volume/volume

mixture of deionized water and ethanol. 1M-Borane/tetrahydrofuran

(THF) complex and (s)-(+)-2-amino-3-methyl-butan-1-ol {(s)-(+)-

valinol) obtained from Aldrich Chemical Company, Inc. were used as

obtained. 1,1,2,2-Tetrachloroethane (TCE) obtained from Aldrich

Chemical Company, Inc. was distilled and stored over molecular

sieves 4X. 1,2-Dichlorobenzene, HPLC grade, obtained from Aldrich

Chemical Company, Inc. was used as obtained. Chloroform obtained

from Fisher Scientific was dried over calcium chloride overnight

before use. THF obtained from Fisher Scientific was dried over

calcium hydride overnight and distilled before used. Pyridine

obtained from Fisher Scientific was distilled and stored over

molecular sieves 4X under nitrogen pressure. Other solvents, e.g.,

acetone, methanol, ethanol, hexane, and petroleum ether were used

with no further purification.

34

Synthesis of Poly[oxv(2-acetvl-1 •4-phenvlene)oxvterephthalovl-co-

oxy(2-acetyl-1 •4-phenvlene)oxyisophthaloyl]

The procedure for the polycondensation reaction was also

taken directly from the process developed by Onwunaka^S, A

schematic for this process can be found in Fig. 12.

2',5'-Dihydroxyacetophenone (4.565 g, 0.0300 mole) was

dissolved into a mixture of 35 mL of dry TCE and 8 mL of dry

pyridine in a 250 mL three necked flask equipped with a mechanical

stirrer, a condenser, a nitrogen inlet and sodium hydroxide moisture

trap. TerephthaloyI chloride (3.66 g, 0.0180 mole) and isophthaloyi

chloride (2.44 g, 0.0120 mole) were dissolved in 35 mL of dry TCE,

and the mixture was added dropwise to the solution of 2',5'-

dihydroxyacetophenone under a nitrogen atmosphere with stirring

for 10 min. An additional 35 mL of dry TCE was gradually added

during the polymerization in order to reduce the viscosity of the

system to facilitate stirring. The mixture was stirred for 12 hrs at

room temperature. Then, the mixture was poured into 300 mL

acetone and precipitated for 12 hrs. The precipitate was filtered,

washed several times with acetone, water, methanol, and petroleum

ether. It was dried in vacuo for 24 hrs at 110 °C. The weight of the

dry product was 7.60 g.

35

TCE, Pyridine

r.t. 12 hrs

Fig. 1 2. Synthesis of Poly[oxy(2-acetyl-1,4-phenylene)oxy-terephthaloyl-co-oxy(2-acetyl-l,4-phenylene)oxy-isophthaloyl]

36

Asymmetric Reduction of Polv[oxv(2-acetvl-1.4-phenylene)oxytere-

phthalovl-cQ-Qxv(2-acetvl-1.4-phenvlene)oxvisophthalovl]

The procedure for the asymmetric reduction was devised using

the model of Itsuno^S^ jn which he reduced low molecular weight

aromatic ketones. Fig. 13 gives a schematic depiction of the

proposed reduction.

The polymer (1.00 g) was dissolved in 50 mL of dry TCE and the

solution was allowed to stand for 24 hrs. The solution was heated

slightly to facilitate solubility. The polymer solution was then

poured into a 125 mL pressure equalizing funnel (A), and stored

under nitrogen atmosphere.

(s)-(+)-Valinol (2.064 g) was dissolved in 10 mL of THF and

then, this valinol/THF solution was charged to a 250 mL three

necked flask equipped with a nitrogen inlet with a sodium hydroxide

moisture trap, a thermometer, pressure equalizing funnel (A),

pressure equalizing funnel (B) with a septum inlet on the top of it, a

condenser, and a magnetic stirrer. IM-Borane/THF complex (40 mL,

40 mmol borane) was charged into funnel (B) under nitrogen pressure

and added dropwise to a stirred valinol solution at -50 °C during 20

min. The solution was gradually warmed to 30 °C and stirred for 10

hrs at that temperature to complete the borane/valinol complex

formation.

37

1. Borane/Valinol THF/TCE 40°C, 8 hrs

2. dil.-HCi

H-C*-OH I CHo

Fig. 13. Asymmetric Reduction of Poly[oxy(2-acetyl-l ,4-phenylene)oxyterephthaloyl-co-oxy(2-acetyl-1,4-

phenylene)oxyisophthaloyl]

38

After the reducing agent complex was formed, the polymer

solution was added dropwise over 10 min and the solution was

stirred for 8 hrs. The resulting mixture was decomposed by 50 mL

of 0.2M-hydrochloric acid over 10 min, and immediately neutralized

by 1M-sodium hydroxide solution. The mixture was poured into 300

mL of acetone, and stirred for 24 hrs. Since no precipitate was

observed, the mixture was directly subjected to rotary evaporation

to remove all solvents. The residue recovered from the mixture was

dried for 24 hrs in vacuo at 110°C. The resulting solid was

dispersed into 300 mL of water, and stirred for 30 min. The

dispersion was filtered, and the solid was washed with water

several times. Then, the solid was dried for 48 hrs In vacuo at

110°C, and 0.5 g of a pink powder was recovered.

39

CHAPTER III

RESULTS AND DISCUSSION

General Comments on Synthesis Method

In his process for the synthesis of Poly[oxy(2-acetyl-1,4-

phenylene)oxyterephthaloyl], Onwunaka devised three different

routes to form the polymer. In each pathway, hydrochloric acid (HCI)

was liberated as a polycondensation by-product. If the removal of

HCI was insufficient during the polymerization, a side-reaction

presented by Haley might occur. For this reason, the author chose

the third of Onwunaka's routes, in which pyridine was used as a HCI

scavenger. The fact that the polymer was synthesized, was

confirmed by FTIR, proton NMR and carbon-13 NMR analyses. The

results will be presented later.

Solubility

Before reduction, the polymer was soluble in 2-chlorophenol,

TCE, and trifluoroacetic acid. It was also partially soluble in

chloroform. It was not soluble in water, methanol, and acetone.

40

The reduced polymer was soluble in 2-chlorophenol, TCE, and

trifluoroacetic acid. It was partially soluble in acetone, methanol,

THF, and chloroform.

Dilute Solution Viscosity

The intrinsic viscosity of the reduced material was 0.11 dL/g

which was much less than that of the polymer before reduction (0.42

dL/g). This decrease of the inherent viscosity was probably caused

by hydrolysis of the ester linkage during reduction and purification.

Spectroscopic Analysis

FTIR

The FTIR spectrum of Poly[oxy(2-acetyl-1,4-phenylene)oxy-

terephthaloyl-co-oxy(2-acetyl-1 ,4-phenylene)oxyisophthaloyl] (the

polymer before reduction) is shown in Fig. 14, and the peak

assignments are given in Table 3. At 3457 cm•^ the polymer shows

a small, broad peak, which is probably a water impurity. The peak at

1738 cm-"" is indicative of the ester carbonyl stretch, while the

ketone carbonyl peak is seen at 1691 cm-''. The stretching

absorption for the ester C-0 is observed between 1014 cm-"" and

41

c o • M

o 13

TJ <U

(H Q)

Q) i _ O

M— <D

CO L_ Q)

E _> O

Q-0)

O

E L -

• M

u

s. I/) cr

D) U.

42

c o 4—'

o Z3

• a CD QC

o

JD

CD

E

o CL (D

W J ^

_ CC

E CD

DC

c CD

E D)

'</3 CO <

J ^ j ^ CC CT3 CD 0

5 $

o> E c Z3 o T3

(D CO

o o o . 0

CO Q) CO

o II

00 E CO

CO

o II X o X O

o < ^ 6 CD *—>

CO Hi

o o CO

O II

O o oS i^

^ j ^ j«: CO CT3 CO CD 0 CD

§ 5 5 > > >

E _2 T3 0

CO 0

J5 CO </5 CO » _ CD 3 Q . O

LL

E 3

"•o 0

O CD

E c o

o) •;= C CO

' . ^ k--9

.S£ "> CO 0 il < '^

T3 CO CJ>

*—> O ) > N

0 C o CO T3 C

JD o 0 CO n o 6 CO X

o 1 _ 0

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CO LU

CO

E • D C

o 0 CO X2

• a 0

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CO O

^ 4-^ 3 3 CO o

CO • ^ +—• 00 0 T t

E • ^

c O)

• ^ O CO CO

E o

00 lO

< h- Cvl o> • r - • ^ ~

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c CO

CO CO 0 CL

>. "* O r- CD c» " O

c CO

CO CO 0 CL

O) CO CO T— •T— o " O

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CO CO 0 CL

0 c UJ

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c ^ _o 4—>

Q. ^ o CO

>> X O

< 4—•

lo 6 o li

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o CO

c o X

O o "co

o k_

0

o o

o V - * CO

0 o c 3

E *—* CO

4—'

0 E n

o c 3

o I—

LU ^ o CO

1-LL < <

0 0

m CO

o 5

Tl-

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CO CO o

CO

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eg

h-

h-

CO X

o Q o

o

43

1240 cm-"" as four strong, sharp peaks. The absorption peak at 717

cm-i is indicative of the aromatic =CH out-of plane bending.

The FTIR spectrum of the reduced polymer is shown in Fig. 15,

and the peak assignments are given in Table 4. When this spectrum

is compared with the spectrum of the starting material, there are

three major differences. The first difference is the disappearance

of the keto C=0 peak at 1691 cm-"", and the second is the increase of

intensity of the broad -OH peak at about 3400 cm-"". The third

difference is the disappearance of the -CHS peaks at 1410 cm-"" and

1358 cm-'' which probably shifted or lost their intensity by

reduction. These three differences imply that the reduction was

successful. However, further characterization by NMR was needed to

confirm this.

Proton NMR

Fig. 16 shows the proton NMR spectrum of the starting

material. The spectrum is characterized by a peak at 2.8 ppm, which

indicates the presence of the methyl protons of the acetyl group, and

aromatic peaks between 7.2 ppm and 9.4 ppm, which indicate the

presence of aromatic protons from the dioxyacetophenoic ring,

terephthaloyi ring, and isophthaloyi ring.

Fig. 17 shows the proton NMR spectrum of the material after

the reduction. Based on proton NMR theory, protons attached to alkyl

44

c o o =J

0)

a: SI

Q)

E o 0)

o E 3 L-+-' o 0) CL

CO

a:

LO

D)

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w J!C k . CC

E 0)

•c c o XS 3

• o 0

oc l _

CD nj k_ CD

E _>s O Q-CD

•D CD

E 3

^ '•B - CD T3

CC ^ O

O) c: o

CO

m

CD

E c O ) C/5 <

- E CC § (D ~ > 0

O) E c 3 o "O

CD 03

x: 1 x: sz t~

CJ

2 _c c

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CO O )

c 4-^ CC 00

CO CO

E CO o II

' k *

o O X o I O V - '

CC 0 6 O 1 < 6 a5 E

o c CC 0

CO

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Q . "co LU < LU

o m 4—" c~ CC

E C o a> CC o •D

0

0 -4—'

CC 3 Q .

« CO o Xi 4—»

3 3 CO o

CO 4—» c 0 E c C3) CO CO

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c o

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LU

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CM CO

C75

CO

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CO 00

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II o o o

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Q_ CL

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C o o :3

TD (U

ai 0) x:

— - c t -

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<U L -

o <+-(U

CO 1_ 0)

E o

Q. (D

~oo

I r— Q 1 -t o

UJ O

z LU =3 O UJ CNJ LO cn CD

1 < a> < t

UJ cn U. Q-en o

1 1 - 5:

ZD •<t

a o t— o z

UJ 1 CM UJ > UJ T - D. t— _J _J CD X < O i - i O UJ Q C/i U .

_ o

O

E 13 L_

4-»

o <D Q .

CO

C O • M

O 1 .

Q.

CD

D)

47

X

a \—

(-0

UJ

o z; UJ Z)

a n LJJ Ow CM

en CD 1

< OJ

< t UJ CM U_ Q_ 00 CNJ

1 1 - S

C\J Z ) xj-Q_ o (— a: Z

><j- UJ 1 1— UJ > UJ

T- D_ H- _J _J CD X < O • - ! O UJ Q CO U .

c o

• + J o •D

"O (U

a: (U

(U • I - '

M—

< 0)

E o

Q_

Q)

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CO

o:

c o • J

o k -

Q.

U)

48

carbons appear between 0 ppm and 3 ppm, alcoholic protons between

3 ppm and 6 ppm, and aromatics between 6.5 ppm and 9 ppm. Thus,

according to the structure of the material after the reduction, a

methyl doublet, a proton quartet from the proton attached to the

carbon which has the alcoholic hydroxyl group, an alcoholic proton

singlet, and aromatic peaks should be observed in each region, but

there are more peaks observed. By comparing this spectrum with the

proton NMR spectrum of valinol shown in Fig. 25, APPENDIX II, some

of the peaks could be assigned as peaks of valinol, but it is still hard

to assign all peaks completely. However, the disappearance of the

methyl peak at 2.9 ppm suggests a successful reduction as discussed

in FTIR spectral characterization.

Carbon-13 NMR

Fig. 18 shows the carbon-13 NMR spectrum of the starting

material. The spectrum is characterized by a peak at 30.5 ppm

which indicates a methyl carbon peak of the acetyl group, fifteen

aromatic carbon peaks between 122 ppm and 152 ppm, two carbonyl

carbon peaks at 169 ppm, and a keto carbon peak at 206 ppm.

Fig. 19 shows the carbon-13 NMR spectrum of the material

after the reduction. Like the proton NMR spectrum, this spectrum is

complicated, and more carbons are observed than those expected

from the reduced polymer's structure. By comparing this spectrum

with the carbon-13 NMR spectrum of valinol shown in Fig. 26,

4V

c o o ZJ

- D <D

a: Q)

JO. +-» Q) i _

o «4— Q)

CQ L -

(U

E o Q-0)

E k-+-» O 0) Q.

CO

a:

CO

c o

XI i _ CO

U

c»

D)

5U

CO

Q 1— t o

UJ

o z UJ 3 o • ^

Ld OvJ CM CO 05

1 < CNJ

< •* u c\j u . Q_ en _ j 1

1 - i .

OJ 3 " * Q., o 1—

i r •z. •<*- UJ

1 oo bJ > UJ

«— Q. 1— _J _1 CD X < O (-1 O UJ Q if) U-

CL D_ c

o O +-» CNJ o 3

• a (U

DC O 0) x f - C

(U

(U

E o

Q_ 0)

o E

o 0) Q.

CO DC

CO

I

c O L . OJ

U

O)

d)

51

APPENDIX II, some of the peaks could be assigned as peaks of valinol,

but it is still hard to assign all of the peaks completely. However,

the disappearance of the keto carbonyl carbon peak at 206 ppm still

suggests a successful reduction.

Conclusion on Spectroscopic Analysis

Based on the characterization of FTIR and NMR spectra, it is

clear that the synthesis of the starting material was successful. It

is also clear that the reduction of the starting material was

successful because no keto carbonyl peaks were observed in both

FTIR and carbon-13 NMR spectra. However, the proton and carbon-13

NMR spectra of the reduced material were too complicated to assign

all peaks, although some of the additional peaks could be assigned as

the peaks of valinol. A possible explanation for the contamination of

the reduced material by valinol is the strong hydrogen bonding

between ester carbonyls in the polymer and alcohol or amino groups

in valinol.

Thgrmal Analy?g?

Fig. 20 and Fig. 21 show the DSC scan and the TGA thermogram

of the polymer before reduction, respectively. The DSC scan shows

52

DSC <Natne>

0Bl_4_p.2 <Date>

92/05/07 10: 43 a i r

-1500

<Sample> 0B1-4-R

5.600 iTig ( 5.600 mg)

<Reference>

<Comment> <Temp. program [C] [C/min] [min]> IK - 5 0 . 0 - 300.0 20.00 1.00

<Gas> 0.0 ml/min 0.0 ml/min

-2375

-3250

-4125

1.000 mg <Sampling> 1.0 sec

-5000 -60 30

qeorala tech school of chem enq

120 210 TEMP C (Heating)

300

Fig. 20. Differential Scanning Calorimetry Thermogram of the Polymer Before the Reduction

53

T6A File Name: obl42 Saddle Height: 15.424 rag Sat Hay 09 15: 54: 31 1992

Ob1-4-2

100.0

PERKIN-ELMER 7 Series Thermal Analysis System

95.0-,

= 90.0

85.0

BO.O -

75.0

70.0

65.0 -

50.0

nitrogen

200.0 250.0 300.0

Tempepatupe ('C)

1 r

350.0 400.0

Takashl

450.0

0.0 Bin NATS i: KO.o C/Bin

Fig. 21. Thermogravimetric Analysis Thermogram of the

polymer before the Reduction

54

endotherms at 140°C, 170°C, and 237°C. The endothernns at 140°C

and 170°C are the nnelting points of different size crystals. The

endotherm at 237°C probably represents the clearing temperature,

but this should be confirmed by POM. The base line shift above

260°C represents the polymer degradation because a significant

weight loss was observed above 250°C in the TGA thermogram (Fig.

21).

Fig. 22 and Fig. 23 show the DSC scan and the TGA thermogram

of the polymer after reduction, respectively. The DSC scan shows

several endotherms at 87°C, 163°C, 196°C, 205°C, and above 270°C.

The endotherm at 87°C probably represents the melting of valinol.

The endotherm at 163°C is the melting point (Tm). The endotherm at

205°C is the boiling point of valinol. No clearing temperature was

observed because of the significant baseline shift above 205°C

caused by the evolution of valinol and polymer degradation (Fig. 23).

Finally, the endotherms above 270°C probably represent the severe

degradation of the polymer.

55

DSC <Name>

0Bl_4_p.l <Date>

<Saniple> 0B1-4-R

5.600 mg ( 5.600 mg)

<Reference>

<Cofnment> <Teinp.program [C] [C/mlnl [min] > 1« - 5 0 . 0 - 300.0 20.00 1.00

<Gas> 0,0 ml/min 0.0 ml/min

92/05/07 10:10 air

1000

-1000-

-3000

u O

-5000

1.000 mg <Sampling> 1.0 sec

-yooo"--60 30

qeorqla tech school of chem enq 120 210

TEMP C (Heating) 300

Fig. 22. Differential Scanning Calorimetry Thermogram of the Polymer After the Reduction

56

TGA File Name: obl4r Sample Weight: 10.742 mg Frl May 08 15:24:06 1992

obl-4-r

PERKIN-ELMER 7 Series Thermal Analysis System

nitrogen

50.0 100.0 150.0 i>00.0 250.0 300.0 350.0 400.0

Temperature (*C) Takashi

450.0 500.0

0.0 sin lUTV ix ao.O C/Bln

Fig. 23. Thermogravimetric Analysis Thernnogram of Polymer After the Reduction

the

57

CHAPTER IV

CONCLUSIONS AND RECOMMENDATION

Conclusions

Poly [oxy(2-acety 1-1,4-phenylene)oxyterephthaloyl-co-oxy(2-

acetyl-1,4-phenylene)oxyisophthaloyl] was synthesized by

applying the procedure of Onwunaka. The synthesis was

confirmed through FTIR and NMR analyses. The intrinsic

viscosity of the polymer was 0.42 dL/g in 2-chlorophenol at

30°C.

The reduction of poly[oxy(2-acetyl-1,4-phenylene)oxytere-

phthaloyl-co-oxy(2-acetyl-1,4-phenylene)oxyisophthaloyl]

was successful since the disappearance of a keto carbonyl

carbon was confirmed through FTIR and NMR analyses.

However, some additional peaks which should not be observed

according to the structure of the reduced material were also

observed in proton and carbon-13 NMR spectra. Some of the

additional peaks could be assigned to the peaks from valinol by

comparing them with proton and carbon-13 NMR spectra of

valinol. The inherent viscosity of the polymer after reduction

58

was 0.11 dL/g, which was much less than that of the polymer

before reduction (0.45 dL/g).

59

Recommendations

The author strongly recommends the future attempts to use

the organic synthetic route indicated in Fig. 24-1 and 24-2. There

will be two major advantages to this method compared with the

polymeric route demonstrated in this thesis. Thq first advantage is

the ease of reduction. Since the reduction will be done at the stage

before polymerization, there will not be any problem dissolving the

material, and the optical yield of reduction, which cannot be

measured when the polymeric route is taken, will also be easily

confirmed. The second advantage will be the absence of any side

reaction caused by the insufficient removal of hydrochloric acid

'\ since the ketone in 2'.5'-dihydroxyacetophenone will have already

been reduced before polymerization. In addition to these advantages,

the protection of alcohol by the trimethylsilyl group etc. is also

preferable to prevent transesterification, which might occur when

the polymer is heated.

A disadvantage of the organic synthetic route is the number of

steps. In the case of the polymeric route , there are only two steps,

polymerization and reduction. The organic synthetic route requires

at least five steps.

In order to accomplish this organic synthetic route. It is

necessary to protect the phenolic hydroxyl group and alcohol

0 0

I. Protection of phenolic -OH

„o-Q-OH CHj

CH / C=0

VJ °^U-\!\J c=o

CH /

2. Asymmetr ic reduction

.CHo

vJ °^J-\AJ c=o

CH /

.CH,

vj °-^r\iyj . H

""< 'OH

Fig. 24-1 Scheme for the Organic Synthetic Route 1

3. Protect ion of the chiral alcoholic -OH

.CHo

v_/ °^Kr\Aj ^ " 3 OH

.CHn

\ // °^ /r\A // CH. . H

^"3 o-Si-CH3

4. Deprotection of phenolic -OH

.CH2

VJ °^^^\;XJ CH ^ ^ \ ' ^ " 3 -"3 0 -S I -CH3

CH3

HO V //

OH

. H

^ O—Si-CHo

CH3

Polymerizat ion w i t h Terephthaloyl Chloride

Fig. 24-2 Scheme for the Organic Synthetic Route 2

6 2

produced by reduction. Methods to protect alcoholic hydroxyl groups

are well established, and one of these routinely used methods should

be adopted. Several methods to protect phenolic hydroxyl groups are

also available, but most of these methods will not work for the

phenolic hydroxyl groups in 2',5'-dihydroxyacetophenone because of

the hydrogen bonding of one of the hydroxyl groups with the ketone

as shown below.

HO

According to current literature, only the protection by methyl ether

and benzyl ether have been successful, but the protection by methyl

ether will be technically more difficult than that by benzyl ether

because the system is heterogeneous and requires phase transfer

reagents. The protection by benzyl ether is a homogeneous reaction

and therefore easier.

• • • i » >

63

APPENDIX

The proton and carbon-13 NMR spectra of valinol are shown in Fig. 25

and Fig.26.

••ii l l l lfHlil lMik

64

X o H-Ui

u o z u cr bJ Ovl

en en

o z

< < UJ CNJ U . 01 rvi t— _J I D t D_ O I—

bJ ' - Ul > UJ a . I— _i _ j X < O n bJ Q t/> U.

6 5

a i / i

UJ

o 2:

^ UJ ff 3 0

- i UJ OJ 0 on CD

1 :lt UJ r\ l i f tn —1

rvJ 1 f- k

Z} • *

o a. 0 1— o 2; z UJ

(—( OJ UJ > UJ

_) D- H- _J _J

< X < 0 t-H

> UJ Q en u_

o c "(i >

M—

o E E •M

o

s. CO Q :

z m c o

XI k -OJ

U <£> OvJ

d)

6 6

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