Title of Invention

A PROCESS FOR PREPARATION OF LIQUID CRYSTALLINE POLYESTERS

Abstract

The present invention provides a process for preparation of liquid crystalline polyesters of formula hydroxyphenylacetic acid and 4- hydroxybenzoic acid has been taken as a copolymer which give copolyesters of better melt processability and thermal stability with the expected nematic meso phase. Moreover, it is a cost effective process for the production of liquid crystalline copolyesters through this route.

Full Text

The present invention relates to a process of preparation of liquid crystalline polyesters. The present invention particularly provides a process for the preparation of homo and copolyesters such as poly(4-oxyphenylacetate) from 4-hydroxyphenylacetic acid and poly(4-oxyphenylacetate- co-4-oxybenzoate] from 4-hydroxyphenylacetic acid and 4-hydroxy benzoic acid. Poly(4-oxyphenylacetate) and Poly(4-oxyphenyl acetate- co- 4-oxybenzoate) were prepared by the process of the present invention has the structure shown in formula I of the drawing accompanying this specification wherein R = nil or -0-C6H 4-CO-. As polyesters prepared by the process of the present invention is a liquid crystalline polymer which can be used in electronics (eg. surface mount units, connectors, printing wiring boards etc. where low coefficient of thermal expansion and low dielectric properties are required), in computer fields, in industry for making chemically resistant parts (eg. tower packing saddles to replace ceramics), in biomedical implants as biodegradable screws and pins , and the industries to which the invention can apply are plastic industries / electronic industries/ computer industries/medicine and * surgery. Thermotropic liquid crystalline homopolyesters obtained from rigid monomers such as 4-hydroxybenzoic acid are intractable, insoluble and not processable because they decompose prior to melting and their transition temperatures are too high for the existing equipments to process them. (A.Blumstein (Ed), Polymeric Liquid Crystals, Plenum Press, NewYork(1985); C.Noel and P. Navard, Progr. Polym. Sci., 16, 55-110 (1991); J. Frank, Z. J. Jedlinski and J. Majnus in Hand Book of Polymer Synthesis, H. R.Kricheldorf (Ed), (1991); W. J. Jackson, Jr. and H. F. Kuhfuss, J.Appl. Polym. Sci., 25, 1685 (1985); A. J. Fast, L. F. Charbenneau and G. W. Calundann, Mol. Cryst. Liq.Inc. Nonlinear Opt, 157, 615 (1988); A. Roviello and A. Sirigu, J. Polym. Sci.Polym. Lett. Edn., 13, 455 (1975); C. K. Ober, J. J. Jin and R. W. Lenz, Adv. Polym. Sci., 13, 103 (1984); A. Blumstein, K. N. Sivaramakrishnan, S. B. Clough and R. B. Blumstein, Mol Cryst. Liq. Cryst. (Lett), 49, 255 (1979); H. R. Kricheldorf and L. G. Wilson, Macromolecules, 27, 1669 (1994); P. K. Bhowmik and H. Han, J. Polym. Sci. Part A : Polym. Chem. 33, 415 (1995); V. Percec and H. Oda, J. Polym. Sci. Part A : Polym. Chem.33, 2359 (1995); J. Economy and K. Goranov, Advances in Polymer Science, Vol. 117, High Performance Polymers, Springer verlag, Berlin, Heidelberg, 1994; C. K. S. Pillai, D. C. Sherrington and A. Sneddon, Polymer, 33, 3968 (1992); M. Saminathan, C.K.S Pillai and C. Pavithran, Macromolecuks, 26, 7103 (1993); J. D. Sudha, C. K. S. Pillai and S. Bera, J. Polym. Mater., 13, 317 (1996); H. Zhang, G. R. Davies and I. M. Ward, Polymer, 33, 2651(1992)). There has been a large number of attempts to bring down the transition temperatures to a processable range (J-I.Jin, C-S. Kang, Prog.Polym.Sci. vol.22,937(1997), H.Han, P.K.Bhowmik Prog. Polym.Sci. vol.22, 1431(1997), W. J. Jackson, Jr. and H. F. Kuhfuss, J.Appl Polym. Sci., 25, 1685 (1985); A. J. East, L. F. Charbenneau and G. W. Calundann, Mol. Cryst. Liq.Inc. Non • Linear Opt. 157, 615 (1988); A. Roviello and A. Sirigu, J.Polym. Sci. Polym. Lett. Edn., 13, 455 (1975); C. K.Ober, J.-I.Jin and R.W.Lenz, Adv. Polym. Sci., 13, 103 (1984); A.Blumstein, K. N. Sivaramakrishnan, S. B. Clough and R. B. Blumstein, Mol. Cryst. Liq. Cryst. (Lett), 49, 255 (1979); H. R. Kricheldorf and L. G. Wilson, Macromolecules, 27, 1669 (1994); V. Percec and H.Oda, J. Polym. Sci . Part A : Polym. Chem.33, 2359 (1995); J. Economy and K. Goranov, Advances in Polymer Science, Vol. 117, High Performance Polymers, Springer verlag, Berlin, Heidelberg, (1994); C. K. S. Pillai, D. C. Sherrington and A. Sneddon, Polymer, 33, 3968 (1992)). A number of chemical approaches have been devised to arrive at structures that have lower tansition temperatures and lower symmetries. These approaches involve disrupting the ordered structures of the homopolyesters by introducing chain disrupters such as flexible unit, a kink structure, or crank shaft srtucture etc. or by copolymerising with suitable comonomers that bring down the transition temperatures by inducing frustrated packing of the molecules by randomisation. A number of copolyesters have thus been prepared out of which a few commercial polymers such as Vectra*, and Xydar*, are well known. It is, however, now realised that these copolyesters are still having a processing temperature above 300°C and hence requires newer methods or structures to overcome this problem. In this situation 4-hydroxyphenyl acetic acid, the monomer that possesses a -CH2- unit between the carboxyl and the rigid phenyl unit and hence expected to bring down the transition temperature when copolymerised stands a significant chance for contributing to solving this problem. The drawbacks of the currently marketed liquid crystalline polyesters are that, polyesters of 4-hydroxy benzoic acid do not form a melt below its decompositon temperature and liquid crystalline copolyesters like 4-hydroxy benzoic acid / polyethylene terepthalate system (Eastman X7G) has several short comings in that the heat distortion temp is low (300°C) processing is rather difficult. We have already shown that the homopolyester of 4-hydroxyphenyacetic acid is a melt processable liquid crystalline polymer exhibiting a clear nematic phase through, Indian patent application number NF 204/97 dated 6.8.1997. So a copolymer of 4-hydroxyphenylacetic acid and 4-hydroxybenzoic acid is expected to give copolyesters of better melt processability and thermal stability with the expected nematic meso phase. Although this is the easiest route to achieve melt processability, there is no publication or patent on the preparation of the liquid crystalline copolyester. Though homopolymerisation of 4-hydroxybenzoic acid is well studied, only a few reports are available on the polymerisation and characterisation of 4- hydroxybenzoic acid containing methylene units between aromatic ring and the carboxyl groups such as 4-hydroxyphenylacetic acid and 3-(4-hydroxyphenyl)propionic acid. There is one report on the preparation of poly(4-hydroxyphenylacetate) (H-G. Elias, R.J.Warner, Makromol. Chem. 182, 681-686 (1981). However, the molecular weight of the polymer is low and the mesqphase behaviour was not studied. The preparation of the copolyester of 4-hydroxyphenylacetic acid and 4-hydroxybenzoic acid would be advantageous when the cost of the final product is compared with the commercial products such as Vectra* and Xydar*. These commercial copolyesters use comonomers such as 2-hydroxy,6-naphthoic acid • and 4,4'-biphenol, which are extremely expensive and therefore, the commercial liquid crystalline polymers are costly. In contrast, 4-hydroxyphenylacetic acid is comparatively cheap and hence, it is possible to achieve a cost effective process for the production of liquid crystalline copolyesters through this route. Moreover it contains aliphatic carbonyl group which is far more electrophilic than the carbonyl group of entirely aromatic hydroxyacids , and therefore more sensitive to hydrolytic degradation . A characteristic advantage of such polyesters is their higher heat distortion temperature and higher Tg compared to aliphatic polyesters. These monomers are nontoxic at low levels and naturally occuring. So these copolyesters will be of application as biodegradable plastics. (H.R.Kricheldorf, T.Stukenbrock, MacromoI.Chem.Phy. 198, 3753, 1997). In these copolyesters by controlling the amount of 4-hydroxyphenyl acetic acid and 4-hydroxybenzoic acid the crystallinity and thus the degradability can be tailor- made or controlled. There are only a few reports on the copolymerisation of 4-hydroxyphenylacetic acid with other hydroxyacids. (K.Imasaka, T.Nagai, MYoshida, H.Fukuzaki, M.Asano, M.Kumakura Jrfakromol.Chem.Wl, 2077, 1990; ). But to our knowledge there is no report on the synthesis of liquid crystalline polyesters from 4-hydroxyphenylacetic acid and 4-hydroxybenzoic acid. The main object of the present invention is to provide a process of preparation of liquid crystalline polyesters. Another object of the invention is , therefore, to provide a process for the preparation of liquid crystalline copolyester having transition temperature lower than that of poly (4- oxybenzoate) and in the processable range below 300°C and having nematic mesophase from 4-hydroxyphenylacetic acid and 4-hydroxybenzoic acid. The main finding underlying the present invention is our observation that •« poly(4-oxyphenylacetate) obtained by the acidolysis polycondensation of 4-acetoxyphenyl acetic acid, prepared by acetylation of 4-hydroxyphenylacetic acid using acetylating agents in presence of catalysts like acetates of sodium, potassium etc., has been found to give mesophase transition at 240°C and isotropises at 260°C. Above 240°C it flows like a liquid with textures correspond to nematic thread. This homopolyester is a thermotropic liquid crystalline polymer having thermal Stability above 340 degree C and better melt processability art 240 degree C. The other main finding underlying the present invention is our observation is that poly(4-oxyphenylacetate-co-4-oxybenzoate) obtained by the acidolysis melt polycondensation of 4-acetoxyphenylacetic acid and 4-acetoxybenzoic acid at 240-260 degree C has been found to give nematic mesophase transition above 260 degree C with textures corresponding to nematic thread. This copolyester is a thermotropic liquid crystalline polymer having thermal stability value of Tj (Temperature at which thermal decomposition is initiated) 400 degree C and better melt processability at 260 degree C. Accordingly the present invention provides a process for the preparation of liquid crystalline polyesters of formula (Formula Removed) Where R=nil or -O-C6H4-CO- which comprises acetylating 4- hydroxyphenylacetic acid by known acetylating agents in the presence of catalysts as herein described at 60-90 degree C for 1-2 hour; and acetoxyderivatives of 4-hydroxybenzoic acid prepared by known methods and polymerizing acetoxyderivatives of carboxylic acid, in the melt at a temperature in the range of 240-260 degree C for a period in the range of 4-6 hours optionally in the presence of high boiling solvent as herein described and continuing the polymerization in the presence of said catalyst under reduced pressure at a temperature 260-280 degree C for 1-2 hours and optionally followed by post polymerization effected at higher temperature below the decomposition temperature for 6-12 hours; and purifying liquid crystalline polyesters by known methods. In an embodiment of the present invention the acetoxyderivative used may be of 4-hydroxybenzoic acid, 4- hydroxyphenylacetic acid and mixture thereof and prepared by conventional acetylating agents used may be such as acetic anhydride, phtalic anhydride, trifluoroacetic anhydride, and chloroacetic anhydride. In another embodiment of the present invention the high boiling solvent used in polymerisation reaction may be such as dibenzylbenzene, chlorobiphenyl, dicyclohexylbiphenyl, chloronaphthalene. In yet another embodiment of the present invention the solvents used in the preparation of acetoxy derivatives are toluene, dichloromethane and diethylether In yet another embodiment of the invention the catalyst used for acetylation of the monomer may be acetates of sodium, potassium, calcium, magnesium. In yet another embodiment of the invention the catalyst used for polymerisation may be such as acetates of lead, copper, magnesium and calcium. Purification of polyesters poly(4-oxyphenylacetae-co-4-oxybenzoate) may be carried out by soxhlet extraction using solvents such as acetone, methylethyl ketone, methylene dichloride, alkanols and mixture thereof. Precipitation of the polymer may be carried out in solvents such as methanol, trifluoro acetic acid , dichloromethane or mixture thereof. The process of the present invention has essentially the following steps: acetylation of the monomer 4-hydroxyphenylacetic acid at 60-90°C for 1-2 hr in presence of acetylating agents, in presence of a catalyst , and acetylation of the second monomer 4-hydroxybenzoic acid in presence of acetylating agents and sodium hydroxide'at ambient conditions; polymerisation of the prepared acetoxyderivatives by acidolysis polycondensation in melt under inert atmosphere , optionally in presence of catalyststs, or high temperature solvent at 240-260°C temperature for 4-6h. Polymerisation was further continued under reduced pressure at a temperature in the range of 260-280°C for a period of 1-2 hr. This was followed by a post-polymerisation step, optionally carried out at a temperature in the range of 240-250°C under inert atmosphere for 6-12 hr , optionally a precipitation step involving trifluoroacetic acid- dichloromethane mixture and methanol, and a purification step involving soxhlet extraction using solvent mixtures such as acetone-alcohol, acetone -methylethyl ketone etc. The invention is described in detail in the following examples which are provided by way of illustration only and should not be construed to limit the scope of the invention. Example 1 In a 100ml R.B.flask, 1.52 gm of 4-hydroxyphenylacetic acid was taken mixed with 6 mg sodium acetate and 10ml acetic anhydride and heated at 80°C for 2 hr by keeping condenser in position and precipitated in 50g crushed ice. Allowed to settle and filtered, dried and recrystallised in toluene. The product was taken in a 60ml polymerisation tube with 0.05% by weight of magnesium acetate and placed in a salt bath heated to 200 °C under slow nitrogen purge. Then temperature is raised to 240°C and kept under stirring for 4 hrs. Then reaction was continued at 260°C for Ihr under vacuum. The tube was cooled to 200°C and removed from the bath and allowed to cool to room temperature and the product was chipped out of the tube. It was then washed with acetone, filtered, dried in an air oven at 65°C for 2 hrs, powdered and further purified by extracting for 24 hrs in a soxhlet extractor using acetone-isopropyl alcohol mixture,. dried under reduced pressure in an air oven at 65°C, to give poly(4-oxyphenylacetate), yield 82%. Example 2 In a 100 ml R.B.flask 3.04g ( 0.02 mol) of 4-hydroxyphenylacetic acid was taken mixed with 10 ml. of acetic anhydride, and 0.05% by weight of potassium acetate and heated at SOT for 2h and precipitated in 50g crushed ice, filtered and recrystallised (I) . In another 100 ml flask 2.76g (0.02 mole) of 4-hydroxy benzoic acid was taken mixed with 0.02mol of sodiumhydroxide in 2ml water, and 10ml of acetic anhydride were added and shaken for lOmin. time and precipitated in 50g crushed ice, filtered and recrystallised (II). In a 60 ml polymerisation tube 1.9g of I and 1.8g of II were mixed in 1:1 mole ratio and evacuated. Then placed the tube in a saltbath heated to 200°C under nitrogen gas pressure for 30min and heated under slow inert gas purge to 240°C and kept at this temperature for 4 hr under constant stirring. Then polymerisation was continued at 0.01mm of Hg pressure for Ihr at a temperature of 260°C. The polymer was chipped out of the tube and purified by soxhlet extraction using acetone / propanol 60:40 mixture for about 18 hr and dried in an air oven at 60°C for about 2 hr at reduced pressure to give poly (4-oxyphenylacetate-co-4-oxybenzoate) , yield 80%. Example 3 In a 100 ml R.B.flask 3.04g ( 0.02 mol) of 4-hydroxyphenylacetic acid were taken mixed withlOml. of acetic anhydride, and 0.1% by weight of calcium acetatae and heated at 100°C for Ih and precipitated in 50 g crushed ice filtered and recrystallised (I). In another 100 ml flask 2.76g (0.02mole) of 4-hydroxy benzoic acid were taken mixed with 0.02mol of sodium hydroxide in 2ml water followed by 10ml of trifluoroacetic anhydride shaken for 15 min. time and precipitated in 50g crushed ice, filtered and recrystallised (II). In a 60 ml polymerisation tube I and n were mixed in 1: 1.5 mole ratio and 0.05% by weight of antimony acetate catalyst was added and evacuated. Then placed the tube in a saltbath heated to 200°C under nitrogen gas pressure for 30min and heated under slow inert gas purge to 250°C and kept at this temperature for 4 hrs under constant stirring. Then polymerisation was continued at 0.01mm of Hg pressure for 1hr at 280°C . Then the polymer was chipped out of the tube and purified by soxhlet extraction using acetone / propanol 60:40 mixture for about 18 hrs and dried in an air oven at 60°C for about 2 hrs.at reduced pressure, to give poly (4-oxyphenylacetate-co-4-oxybenzoate), yield 82%. Example 4 In a 100 ml R.B.flask 1.52g ( 0.01 mol) of 4-hydroxyphenylacetic acid was taken mixed with 5 ml. of acetic anhydride, and 0.05% by weight of Potassium acetate and heated at 80°C * for 2h and precipitated in 50g crushed ice, filtered and recrystallised (I). In another 100 ml flask 1.38g (0,01 mole) of 4-hydroxy benzoic acid was taken mixed with 10ml of acetic anhydrideshaken for lOmin. time and precipitated in 50g crushed ice, filtered and recrystallised (n). In a 60 ml polymerisation tube I and II were mixed in 1:1.5 mole ratio and 0.05% by weight of Zinc acetate catalyst and 5 ml chloronaphthalene highboiling solvent were added and evacuated. Then placed the tube in a saltbath heated to 200°C and heated under slow inert gas purge to 250°C and kept at this temperature for 6 hrs under constant stirring. Then polymerisation was continued at 0.01mm of Hg pressure for Ihr at 280°C . Then the polymer was chipped out of the tube and purified by soxhlet extraction using acetone / propanol 60:40 mixture for about 18 hrs and dried in an air oven at 60°C for about 2 hr. at reduced pressure, to give (4-oxyphenylacetate-co-4-oxybenzoate), yield 83%. Example 5 In a 100 ml R.B.flask 3.04g ( 0.02 mol) of 4-hydroxyphenylacetic acid was taken mixed with 10 ml. of acetic anhydride, and 0.05% by weight of calcium acetate and heated at 80°C for 2h and precipitated in 50g crushed ice, filtered and recrystallised (I). In another 100 ml flask 2.76g (0.02 mole) of 4-hydroxy benzoic acid was taken mixed with , 0.02 mol of sodiumhydroxide in 2ml water, and 10ml of acetic anhydride shaken for lOmin. time and precipitated in 50g crushed ice, filtered and recrystallised (II). In a 60ml ml polymerisation tube 0.06mol of I and 0.04 mol of n were mixed and mixed with O.Olmmol of magnesium acetate catalyst and heated slowly under slight pressure for Ih at 240 °C by heating in a salt bath at slow nitrogen purge and kept at this temperature for 3hrs under constant stirring. Then polymerisation was continued at 0.01mm of Hg pressure for 2hrs. Then the polymer was dissolved in 20ml of 1:4 mixture of trifluoroacetic acid and dichloromethane, and precipitated in 50ml of methanol, filtered and washed free of acid and dried in an air oven at 60°C for about 2hrs. at reduced pressure to give poly (4-oxyphenylacetate-co-4-oxybenzoate), yield 80%. Example 6 In a 100 ml R.B.flask 3.04g ( 0.02 mol) of 4-hydroxyphenylacetic acid was taken mixed with 10 ml. of trifluoroacetic anhydride, and 0.05% by weight of Sodium acetate and heated at 80°C for 2h and precipitated in 50g crushed ice, filtered and recrystallised (I). In another 100 ml flask 2.76g (0.02 mole) of 4-hydroxy benzole acid was taken mixed 0.02mol of sodium hydroxide and 2ml water and 10ml of acetic anhydride shaken for lOmin. time and precipitated in 50g crushed ice, filtered and recrystallised (II). In a 60 ml polymerisation tube 0.06mol of I and 0.05 mol of n were mixed and mixed with O.Olmmol of calcium acetate and heated in a salt bath to 240 °C at slow nitrogen purge and kept at this temperature for 6hrs under constant stirring. Then polymerisation was continued at 0,01mm of Hg pressure for 1hr. Then the polymer was dissolved in 20ml of 1:4 mixture of trifluoroacetic acid and dichloromethane, and precipitated in 50ml of methanol, filtered and washed free of acid and dried in an air oven at 60°C for about 2hrs. at reduced pressure. The polymer is then heated under nitrogen purge for 6h at 240 °C and soxhlet extracted with acetone -isopropanol mixture and dried at 80°C for 1h. poly (4-oxyphenylacetate-co-4-oxybenzoate), yield 80%. Example 7 In a 100ml R.B.flask, 1.4 gm of 4-hydroxyphenylacetic acid was taken mixed with 6 mg magnesium acetate and 10ml acetic anhydride and heated at 60°C for Ih by keeping condenser in position and precipitated in 50g crushed ice. Allowed to settle and filtered, dried and taken in a 60ml polymerisation tube with 0.01% lead acetate and placed in a salt bath heated to 200 °C under slow nitrogen purge. Then temperature is raised to 240°C and kept under stirring for Ihr. Then 5ml of dicyclohexylbiphenyl were added and the reaction was continued at 250°C for Ihr and then raised the temperature to 260°C for 2hr more. Then continued the reaction under vacuum for Ihr. The tube was cooled to 200°C and removed from the bath and allowed to cool to room temperature and the product was chipped out of the tube. Dissolved in 20ml of trifluoroacetic acid :dichloromethane 1:4 mixture and precipitated by adding in 50ml methanol, washed free of acid , filtered, dried. Further purified by extracting for 24 hrs in a soxhlet extractor using acetone-isopropyl alcohol mixture. It was then further dried under reduced pressure in an air oven at 65°C forlh. The polymer was further heated under nitrogen atmosphere at 240°C for 12h . The advantages of the present invention are the following: The present invention provides a process for the preparation of melt processabe liquid crystalline polyesters from 4-hydroxyphenylacetic acid. The liquid crystalline polyester obtained from 4-hydroxyphenyl acetic acid and 4-hydroxybenzoic acid of formula shown in formula 1 of the drawing acccompanying this specification where R = nil or -0-C6H4-CO- has a transition temperature at 240-260°C which is lower than those (300°C) of the commercial liquid crystalline copolyesters such as Vectra* and Xydar*. Hence, the liquid crystalline polyester obtained by the process of the present invention can be melt processed at a temperature of 240-260°C which is lower than that of Vectra* and Xydar* and this may solve many ofcthe processing problem s associated with the existing commercial liquid crystalline polymers. The liquid crystalline polyester obtained by the process of the present invention does not decompose before isotropisation whereas poly(4-oxybenzoate) decomposes prior to melting. As the present invention described by the present process of preparation of liquid crystalline polyester from 4-hydroxyphenylacetic acid does not use a comonomer which is expensive, the cost of the liquid crystalline polyester obtained by the present process is rather low when compared to those of Vectra* and Xydar*. Commercial copolyesters use comonomers such as derivatives of hydroxynaphthoic acid and biphenol which are expensive and therefore, the commercial liquid crystalline polymers are costly. In contrast, 4-hydroxyphenylacetic acid , the comonomer used in the preparation of the copolyester prepared by the process of the present invention, is comparatively cheap. The process of the present invention has a step of post-polymerisation optionally whereby a higher molecular weight is obtained so that the properties of the polymer are better. This copolyester has got comparatively higher decomposition temperature, Ti of 400°C which is higher compared to poly(4-hydroxyphenylacetate). It shows drastic reduction in viscosity due to nematic mesophase which is required for the further processing by injection molding. Moreover these copolyesters are biodegradable. We claim; 1. A process for preparation of liquid crystalline polyesters of formula I whieh comprisfes racetylatmg 4- hydroxyphenylacetic acid by known acetylating agents in the presence of catalysts as herein described at 60-90 degree C for 1-2 hour; and acetoxyderivatives of 4-hydroxybenzoic acid prepared by known methods and polymerizing acetoxyderivatives of carboxylic acid, in the melt at a temperature in the range of 240-260 degree C for a period in the range of 4-6 hours optionally in the presence of high boiling solvent as herein described and continuing the polymerization in the presence of said catalyst under reduced pressure at a temperature 260-280 degree C for 1-2 hours and optionally followed by post polymerization effected at higher temperature below the decomposition temperature for 6-12 hours; and purifying liquid crystalline polyesters by known methods. 2. A process as claimed in claim 1, wherein the acetylating agents are selected from the group of acetic anhydride, phtalic anhydride, trifluoroacetic anhydride, and chloroacetic anhydride, 3. A process as claimed in claim 1, wherein the acetoxy derivative of carboxylic acid used may be such as 4- hydroxyphenyl acetic acid, 4- hydroxybenzoic acid and mixture thereof. 4. A process as claimed in claim 1, wherein the catalysts used for the preparation of the acetoxyderivative of 4- hydroxylphenylacetic acid is acetates of sodium, potassium, magnesium, calcium. 5. A process as claimed in claim 1, wherein the catalyst used in the polymerization step is catates of copper, magnesium, lead, calcium, zinc, antimony. 6. A process as claimed in claim 1, wherein the high boiling point solvent used during the polycondensation step is dibenzylbenzene, chlorobiphenyl, cyclohexylbiphenyl, dicyclohexylbiphenyl, chloronaphthalene. 7. A process as claimed in claim 1, wherein known method used for the purification of polyesters is soxhelt extraction using solvent such as acetone, methylethyl ketone, methylene dichloride, alkanols and mixture thereof. 8. A process as claimed in claim 1, wherein precipitation of the polymer is carried out in solvents such as methanol, trifluoro acetic acid, dichlromethane or mixture thereof. 9. A process for preparation of liquid crystalline polyesters substantially as herein described with reference to the examples and drawing accompanying the specification.

Documents:

1459-del-1999-abstract.pdf

1459-del-1999-claims.pdf

1459-del-1999-correspondence-others.pdf

1459-del-1999-correspondence-po.pdf

1459-del-1999-description (complete).pdf

1459-del-1999-drawings.pdf

1459-del-1999-form-1.pdf

1459-del-1999-form-19.pdf

1459-del-1999-form-2.pdf

abstract.jpg