WO1991017137A1

WO1991017137A1 - Novel monomers and process to synthesize liquid crystalline polyesters

Info

Publication number: WO1991017137A1
Application number: PCT/US1991/002883
Authority: WO
Inventors: Simon W. Kantor; Robert W. Lenz; William J. Ward
Original assignee: The University Of Massachusetts At Amherst
Priority date: 1990-05-01
Filing date: 1991-04-26
Publication date: 1991-11-14
Also published as: EP0527201A1; CA2082830A1; JPH05507514A; EP0527201A4

Abstract

Alkylene bis(acetoxybenzoate) monomers of formula (I), where Ar is substituted or unsubstituted phenyl and r ranges from about 3 to about 8, can be used to synthesize liquid crystalline polyester compositions when reacted with terephthalic acid. Liquid crystalline polyesters of the aromatic triad type are formed by reaction of the alkylene bis(acetoxybenzoate) monomer described above and an aromatic dicarboxylic acid monomer with removal of acetic acid by-product therefrom.

Description

NOVEL MONOMERS AND PROCESS TO SYNTHESIZE LIQUID CRYSTALLINE POLYESTERS

BACKGROUND OF THE INVENTION

In recent years, a great deal of attention has been directed to liquid crystalline polymers. One system studied in detail contains an aromatic ester triad with a central terephthaloyl unit and two terminal oxybenzoyl units connected by a flexible polymethylene spacer of varying length. Fig. 1 , which forms a portion of the instant specification, illustrates the structure of this known aromatic ester triad. References which related to the synthesis and evaluation of such known structure include: C. Ober et al.. Polymer J. 14, 9 (1982); G. Galli et al., Makromol. Chem. 183, 2693 (1982); and A. Y. Bilibin et al., Makromol. Chem. 186, 1575 (1985). The polymers just described have been shown to be thermotropic liquid crystalline polymers which can exhibit either a nematic or a smectic mesophase.

Liquid crystalline polyesters can be synthesized by step-growth polymerization techniques. Two basic methods are generally used. The first involves growing the polymer from solution involving the reaction of a diol with a diacid chloride. The problem of polymer solubility, however, can be a limiting factor in the preparation of high molecular weight polymers, especially in the case of aromatic polyesters. The second method avoids such problems by carrying out the reaction in the absence of solvent. Such bulk (or melt) polymerization techniques (see V. V. Korshak et al., "Experimental Methods of Bulk Polymerization", Comprehensive Polymer Science, Vol. 5, G. Allen, ed., Perga on Press, Oxford, 1989) , usually involve either the reaction of dicarboxylic acids (or their alkyl esters) with diols or the reaction of diacetates with dicarboxylic acids, in the presence or absence of a catalyst. The bulk method works best when the reacting functionalities are directly attached to the aromatic rings. It has been shown by previous investigators that the aromatic triad polyester, a preferred embodiment of which is shown by structure (B) in Fig. 3 and which is more generically depicted in Fig. 1, exhibits a nematic crystalline phase upon melting. A reference which discusses this type of liquid crystalline polyester is C. Ober et al., supra. Such a polymer has been prepared from solution but had a relatively low molecular weight due to solubility problems.

DESCRIPTION OF THE INVENTION

The present invention relates, in one aspect, to novel monomers which can be used as precursors in the synthesis of the triad polymers previously described. Fig. 2 shows a synthesis route which can be used to make these monomers which are alkylene bis(p-acetoxybenzoate) compounds. It is contemplated that the phenyl rings in these compounds can be independently substituted with such substituents as lower alkyl, aryl, halogen and the like.

The alkylene bis(p-acetoxybenzoate) monomers which form one embodiment of the instant invention are, for example, of the formula of the end product from the synthesis reaction shown in Fig. 2 which depicts butylene bis(p-aσetoxybenzoate) , when r = 4, and hexamethylene bis(p-acetoxybenzoate) , when r = 6. In general, the monomers which are intended to be the subject of the invention can have r range from about 3 to about 8.

The preparation of the novel monomers is exemplified in Examples 1 and 2 which follow and involves the initial reaction of an acetoxybenzoic acid (1) in Fig. 2 with thionyl chloride to form the corresponding acetoxybenzoyl chloride (2) which is reacted with a dihydroxy compound of the formula

HO(CH₂)_rOH, where r is as defined above, in the presence of an acid acceptor, such as pyridine.

The instant invention, in another aspect, also relates to preparation of the aforementioned type of aromatic triad liquid crystalline polymer by reaction of the foregoing type of alkylene bis(aσetoxybenzoate) monomer with an aromatic dicarboxylic acid monomer to form the desired aromatic triad polyester with liberation of acetic acid by-product.

A representative alkylene bis(acetoxybenzoate) monomer is depicted by (A) in Fig. 3 with the alkylene group being hexamethylene, namely -(CH₂)₆-. If desired, the phenyl rings can be independently substituted with such substituents as lower alkyl, aryl, halogen, and the like. The alkylene group can be varied in its length, as described before, and can be generically depicted as -(CH₂)_r with r ranging from 3 to 8. As depicted in Fig. 3, this monomer (A) can be reacted with a dicarboxylic acid compound, such as terephthalic acid, in the absence of or, preferably, in the presence of a catalyst such as zinc acetate, using heat to produce the desired aromatic triad liquid crystalline polyester (B) with acetic acid by-product which is easily removed. The dicarboxylic acid reactant can have its phenyl ring substituted by the same substituents described above. Copolymers with mixtures of monomers, e.g., with 50 mole % of a monomer where r is 4 and 50 mole % of a monomer where r is 6 may be prepared. These ratios can be widely varied to cover the entire compositional range (e.g., l%-99% to 99%-l%) .

The instant process is one which is deemed to allow for synthesis of the type of aromatic triad polyester (B) in increased molecular weight as compared to solution methods. Of considerable importance is that the acidolysis reaction does not occur to any extent between the carboxylic acid function and the internal diol ester groups so that essentially no scrambling of the units occurs. The process produces acetic acid as a by-product which can easily be removed under vacuum (see U.S. Patent No. 3,772,405 of F. L. Hamb) .

The instant invention is further understood by the Examples which follow. EXAMPLE 1

This Example illustrates the preparation of butylene bis(p-acetoxybenzoate) which is the final compound depicted by 3a in the equation shown in Fig. 2. An amount equalling 93.5 grams of 4-acetoxybenzoic acid (Compound 1 in the reaction shown in Fig. 2) was mixed with 150 ml of thionyl chloride and stirred at 50°C for 3.5 hours. The excess thionyl chloride was removed under reduced pressure, and the remaining oil was vacuum distilled, and was then recrystallized in hexane, giving pure 4-acetoxybenzoyl chloride (Compound 2 in Fig. 2) with a melting point of 28°C at 75% yield. An amount equalling 40.0 grams (0.20 mole) of Compound 2 was then dissolved in 125 ml of anhydrous chloroform and was warmed with stirring. To this mixture was added dropwise a solution of 1,4-butanediol (7.86 grams, 0.087 mole) in 25 ml of chloroform and 45 ml of pyridine. After the addition was complete, the reaction mixture was heated to reflux with stirring for twenty-four hours. At the end of this period, the reaction mixture was cooled and was washed with water. The organic layer was separated and was washed with a dilute hydrochloric acid solution, then with a 5% sodium bicarbonate solution, followed by a final water wash. The organic layer was dried over CaCl₂ and the solvent was removed. The resulting crude solid was recrystallized once from methanol, then once from acetonitrile, giving butylene bis(p-acetoxybenzoate) with a melting point of 106°C, as a fine white powder in 56% yield.

Analysis for (3a, C₂₂H₂₂0₈) : Calculated: C, 63.76; H, 5.35. Found: C, 63.75; H, 5.35. The proton NMR spectrum was consistent with the desired structure. EXAMPLE 2

This Example shows preparation of hexamethylene bis(acetoxybenzoate) which is compound 3b in Fig. 2.

Hexamethylene bis(acetoxybenzoate) was prepared and purified in a manner similar to the preparation described in Example 1 for the analogous butylene compound. Thus, 4-acetoxybenzoyl chloride (34.5 grams, 0.174 mole) was reacted with hexanediol (8.92 grams, 0.075 mole), to give the desired compound in 63% yield. It had a melting point of 84-85^βC. Analysis for (3b, C₂₄H₂₆0₈) : Calculated: C, 65.15; H, 5.92. Found: C, 65.28; H, 5.93.

The proton NMR spectrum was consistent with the desired end product.

EXAMPLE 3

An amount equalling 3.800 grams of the diacetate monomer, represented by "(A)" in Fig. 3, was combined with 1.427 grams of terephthalic acid and 0.050 gram of zinc acetate, and the solids were thoroughly mixed with a mortar and pestle. The solid mixture was then placed into a reaction tube, and flushed with argon, and a slow stream of argon was passed through the reaction tube. The reaction tube was then placed in a hot salt bath at 180°C, and the temperature was slowly raised to 250°C over a period of two hours. The reaction temperature was then raised to 270°C and held there for two and one-half hours. Finally, a high vacuum was applied, and the reaction temperature was raised to 290°C for one hour. The product was removed and ground, then treated at 215°C for twenty hours under vacuum to induce further reaction and increase the molecular weight of the product (see German Offen. No. 2,520,820, U.S. Patent No. 3,991,013, and H. R. Dicke et al., J. Poly . Sci., Polym. Chem. Ed., 21, 2581, 1983) . The product was then extracted with methanol and dried in a vacuum oven, to give 2.0 grams of polymer.

The product was examined under an optical polarizing microscope and found to display a nematic schlieren texture. The polymer (B) exhibited a melting point of 241°C, and an isotropization temperature of 345°C, as determined by DSC. The inherent viscosity was measured to be 0.540 dl/g at 45.5°C in p-chlorophenol.

Analysis for C₂₈H₂₄0₈: Calculated: C, 68.84; H, 4.95. Found: C, 68.71; H, 4.79. EXAMPLE 4

This Example shows the preparation of a triad copolymer (B) of Fig. 3, where r = 4,6 (50/50).

An amount equalling 3.020 grams of the diacetate monomer "(A)", where r = 4, was combined with 3.224 grams of the diacetate monomer "(A)", where r = 6, and 2.421 grams of terephthalic acid, along with 0.050 gram of zinc acetate. The solids were thoroughly mixed and placed into a reaction tube, and flushed with argon, and a slow stream of argon was passed through the reaction tube. The reaction tube was then placed in a hot salt bath at 180°C. The reaction temperature was then slowly raised to 295°C over a period of 6 hours. A high vacuum (less than 0.1 mm Hg) was then applied to the reaction tube with heating at 295°C for an additional hour. The product was removed and ground, then treated at 180-192°C for six hours under vacuum to induce further reaction and increase molecular weight. The product was then extracted with methanol and dried in a vacuum oven, to give 2.8 grams of polymer. The product was examined under an optical polarizing microscope and found to display a nematic schlieren texture. Analysis of the polymer (B) , where r = 4,6 (50/50), by DSC revealed two endotherm peaks at 174°C and 204°C. The isotropization temperature was above the decomposition temperature, which began at 308°C as determined by TGA. The inherent viscosity was 0.42 dl/g at 45.7°C in p-chlorophenol.

Analysis for C₅₄H_A40₁₆: Calculated: C, 68.35; H, 4.67. Found: C, 68.10; H, 4.67. EXAMPLE 5

This Example shows preparation of a triad polymer of the general structure B in Fig. 3 where the repeating methylene unit is four carbons rather than six. An amount (4 gm) of diacetate monomer A (with r = 4) was combined with 1.603 gm of terephthalic acid and 0.050 gm of zinc acetate and the solids were thoroughly mixed. The solid mixture was then placed into a reaction tube and was flushed with argon and a slow stream of argon was passed through the reaction tube. This reaction tube was then placed in a hot salt bath at 180°C, and the temperature was slowly raised to 285°C over a period of five hours. A high vacuum (less than 0.1 mm Hg) was applied, and the reaction temperature was raised to 295°C for one and one-half hours. The product was then removed, was ground and was then treated at 250°C for two hours under a high vacuum (less than 0.1 mm Hg) . The product was then extracted with methanol and was dried in a vacuum oven to give 3.4 gm of polymer.

The product was examined under an optical polorizing microscope and was found to display a nematic schlieren texture. The polymer exhibited a melting point of 243°C. The isotropization temperature, which was 340°C, as determined by TGA. The inherent viscosity was to be 0.524 dl/g at 45.6°C in p-chlorophenol. Analytical calculations for C₂₆H₂₀O₈: C, 67.82; H, 4.38. Found: C, 67.40; H,4.32

The foregoing Examples should not be construed in a limiting sense since it is intended to describe only certain embodiments of the instant invention. The scope of protection sought is set forth in the claims which follow.

Claims

We Claim:

1. A monomer for use in the synthesis of liquid crystalline polyesters which is of the formula

0 0 0 0

It II II II

CH₃C0ArC0(CH₂)_r0CAr0CCH₃

where Ar is substituted or unsubstituted phenyl and r ranges from about 3 to about 8.

2. A monomer as claimed in Claim 1 where r is 4.

3. A monomer as claimed in Claim 1 where r is 6.

4. A process for forming a liquid crystalline polyester resin of the aromatic triad type which comprises reacting an alkylene bis(acetoxybenzoate) monomer and an aromatic dicarboxylic acid monomer with removal of acetic acid by-product.

5. A process as claimed in Claim 4 wherein the alkylene group is C₃ to C₈ alkylene.

6. A process as claimed in Claim 4 wherein a zinc acetate catalyst is additionally present.

7. A process as claimed in Claim 4 wherein the aromatic dicarboxylic acid monomer is terephthalic acid.

8. A process as claimed in Claim 7 wherein the alkylene group is C₃ to C₈ alkylene.

9. A process as claimed in Claim 8 wherein a zinc acetate catalyst is additionally present.