Title of Invention

"A PROCESS FOR THE PREPARATION OF MELT PROCESSIBLE LIQUID CRYSTALLINE TERPOLYESTERS"

Abstract

Malt processable liquid crystalline terpolyesters of the formula I below: where R is cl, C6H5, CH3CO, CH3 and process for the preparation thereof are disclosed The process comprises acetylating 8(3-hydroxyphenyI) octanoic acid and bydroquinone using aa acetylating agent followed by acidolysis polycondeosation for the removal of acetic acid to effect higher molecular weight formation, pott-polymerisation being effected at higher temperatures but below the decomposition temperature.

Full Text

PROCESS FOR THE PREPARATION OF MELT PROCESSIBLE LIQUID CRYSTALLINF TERPOLYESTERS Field of the invention The present invention relates to a process for the preparation of melt processable liquid crystalline terpolyesters. The terpolyesters of the invention have the structure shown in formula I below: (FormulaRemoved) where R is CL C5H6. CH3CO. CH3 Formula I The terpolyesters prepared by the process of the present invention are poly (4-phenylene naphthalene -2,6-carboxylate -co- 8 (3- oxyphenyl) octanoate), poly (4 - phenylene, 2 -methoxynaphthalene -2,6- carboxylate - co - 8 (3 - oxyphenyl) octanoate), poly (4 - phenylene 2 -phenyl naphthalene - 2, 6 - carboxylate -co - 8 (3 - oxyphenyl) octanoate) and related terpolyesters. The terpolyesters prepared by the process of the present invention are liquid crystalline polymers which can be used in electronics (eg. surface mount units, connectors, printing wiring boards etc. where-low--coefficient-of thermal expansionon-and-low dielectric-properties are required in computer-fields, in industry for making chemically resistant part (eg. tower packing saddles to replace ceramics). The industries to which the invention can apply are plastic industries / electronic industries/ computer industries. Background of the invention Thermotropic liquid crystalline terpolyesters 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 equipment to process them. (A. I Isayev, T. Kyu and S. Z. D. Cheng, Liquid Crystalline Polymer Systems: Technological Actvances. American Chem,cal Society, Washington, DC, 1996.; H. Stegemeyer, Guest Ed., Liquid CryS,als. in Topics in Physical Chemistry (Eds. H. Baumgartel, E. U. Franck and W. Grunbein), Vol. 3, Steinkopff Darmstdt, Springer, New York, 1994; L. L. Chapoy, Ed.: -Recent Advances m Liquid Crystalline Polymer" Elsevier, London, 1985 A. Blumstein (Ed), Polymeric Liquid Crystals, Plenum Press, New York (1985); C. Noel and P. Navardr Progr. Polym. Sci., 16. 55-110 (1991); Jan Frank, Zbigmew J. Jedlinski and J. Majnus in Hand Book of Polymer Synthesis, H. R. Kricheldorf (Ed), (1991); W. J. Jackson, Jr. and H. F. Kuhfuss,./ Appl. Polym. Sci.. 25. 1685 (1985); A. J. East. L. F. Charbenneau and G. W. Calundann. Mol. Cryst. Liq. Inc. Non Linear Opt. 157, 635 (1938); A. Rovielio and A. Sirigu../ 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. Blamstein, K. N. Sivaramakrishnan, S. B. Cloughand 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, Berlir., 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, Macromolecules. 26, 7103 (1993); J. D. Sudha, C. K S. Pillai and S. Bera. J. Polym. Mater.., 13, 317 (1996); H. Zhana. G. R. Davies and I. M. Ward, Polymer, 33. 2651(1992)). There have been a large number of attempts to bring down the transition temperatures to a processable range (W. J. Jackson. Jr. aid H. F. Kuhfuss,.J. Appl. Polym. Sci.. 25, 1685 (1985,). A J East, L. F. Charbenneau and G. W. Calundann, Mol. Cryst. Ijq. Inc. Non Linear Opt, 157, 615 (1988); A. Rovielio and A. Singu, J. Polym. Set. 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. Sivaramaknshnan, 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. Pan 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 transition 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 structure etc. or by copolymerising with suitable comonomers that bring down the transition temperatures (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, Mo/. 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. 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)). 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 still have-a processing temperature above 300°C and hence require newer methods or structures to overcome this problem. It is well known that introduction of disrupters such as a "kink" or flexible segments brings down the transition temperature of liquid crystalline polyesters to a processable range (J. Economy and K. Goranov, Advances_in Polymer Science. Vol. 117, High Performance Polymers, Springer verlag. Berlin, Heidelberg, 1994; A. I. Isayev, T. Kyu and S. 2 D. Cheng, Liquid Crystalline Polymer Systems: Technological Advances. American Chemical Society, Washington, DC, 1996). It has been shown that copolymerisation of hydroxy benzoic acid with comonomers having kink or flexible structures gives rise to decrease in the transition temperatures. Although a variety of comonomers containing such structural features have been employed for the synthesis of liquid crystalline copolyesters, use of a comonomer having both a kink and flexible segment built into the same molecule is rare. 8(3- hydroxyphenyl)octanoic acid is, thus, a comonomer having both kink and flexible segments in its structure which when copolymerised with hydroxy benzoic acid gave a transition temperature as low as 256°C (C. K. S. Pillai, D. C. Sherrington and A. Sneddon, Polymer, 33, 3968 (1992)); However, it was noted that this polymer although liquid crystalline, decompose before melting( Rajalekshmi, M. Saminathan, C.K.S. Pillai and C.P.Prabhakaran, J. Polym. Sci., Polym. Chem., 34, (2851) 1996). It was therefore thought that appropriate substitution in the phenolic ring may give rise to meltable polymers 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 rneit below its decomposition temperature and liquid crystalline copolyesters like 4-hydroxy benzoic acid / polyethylene terepthalate system (Eastman X76) has several shortcomings in that the heat distortion temp is low ( It is an object of the invention to provide novel melt processible liquid crystalline terpolyesters. It is a further object of the invention to provide novel liquid crystalline terpolyesters having transition temperature lower than that of poly (4- hydroxybenzoic acid) and in the processible range below 300 °C and having nematic mesophase from naphthalene dicarboxylic acid, hydroquinones and 8-(3 hydroxy phenyl) octanoic acid. It is a further object of the invention to provide liquid crystalline melt processable terpolyesters that do not decompose before melting. Another object of the invention is to provide melt processable liquid crystalline terpolyesters that do not use expensive monomers. A further object of the invention is to provide a liquid crystalline terpolyester that results in a higher molecular weight polymer. It is yet another object of the invention to provide a process for the preparation of a melt processable liquid crystalline terpolyester. It is a further object of the invention to provide a process for the preparation of liquid crystalline melt processable terpolyesters that do not decompose before melting. Another object of the invention is to provide a process for the preparation of melt processable liquid crystalline terpolyesters that do not use expensive monomers. A further object of the invention is to provide a process for the preparation of a liquid crystalline terpolyester that results in a higher molecular weight polymer. Summary of the invention Accordingly the present invention provides novel melt processable liquid crystalline terpolyesters of the formula I below: (Formula Removed) where R is Cl. C6H5. CH3CO. CH3 Formula I In one embodiment of the invention , the novel terpolyesters of the invention are poly(4-phenylene naphthalene -2,6-carboxylate-co-8(3-oxyphenyl) octanoate)s, poly(4-phenylene,2 methoxynaphthalene-2,6- carboxylate-co-8(3-oxyphenyl) octanoate)s , poly(4-phenylene 2-phenylnaphthalene -2,6-carboxylate-co-8(3-oxyphenyl) octanoate)s and related terpolyesters. Accordingly the present invention provides a process for the preparation of melt processible liquid crystalline terpolyesters said process comprising acetylating 8(3-hydroxyphenyl) octanoic acid and hydroquinone using an acetylating agent as defined herein, followed by acidolysis polycondensation in presence of a transesterification catalyst, such as herein described, at a temperature in the range of 240° - 280°C for a period of 6 - 24 hrs, under reduced pressure of 1 - 3m of Hg for the efficient removal of acetic acid to effect higher molecular weight formation, post-polymerisation being effected at higher temperatures at the range of 250°C - 300°C, in presence of high temperature solvent such as herein described, for a period of 42 - 72 hrs, followed by purification by soxhlet extraction using solvent mixtures selected from the group comprising of acetone-alcohol, acetone-methylethyl ketone to get desired terpolyesters. In one embodiment of the invention, the acidolysis polycondensation is carried out in the optional presence of a high temperature solvent. In another embodiment of the invention , the acidolysis polycondensation is carried out in the optional presence of a transesterification catalyst. In a further embodiment of the invention the transesterification catalyst used in the polycondensation step is selected from the group comprising of acetate of lead , magnesium , cobalt, antimony , zinc and the like. In a further embodiment of the invention the metal acetate catalyst is selected from the group comprising of lead acetate, calcium acetate, zinc acetate, antimony triacetate. In yet another embodiment of the invention the high temperature solvent used is selected from the group comprising of dibenzyl benzene, Marlotherm, Dowtherm both derivatives of dibenzyl benzene In a further embodiment of the invention the acetylating agent used is selected from the group comprising of phthalic anhydride, trifluoroacetic anhydrided acetic anhydride, chloroacetic anhydride. In a further embodiment of the invention , a postpolymerisation reaction is carried to improve molecular weight of the polymer The main finding underlying the present invention is our observation that poly(4-phenylene naphthalene -2,6-carboxylate-co-8(3-oxyphenyl) octanoate)s, poly(4-phenylene,2- methoxynaphthaIene-2,6- carboxylate-co-8 (3-oxyphenyl)octanoate)s, poly(4-phenylene,2-phenyl naphthalene-2,6- carboxylate -co-8(3-oxyphenyl) octanoate)s and related terpolyesters prepared by the process of acidolysis melt polycondensation of 2,6 naphthalene dicarboxylic acid with diacetoxy benzene and 8 -(3 acetoxy phenyl) octanoic at 280°C have been found to give nematic mesophase transition in the range of @ 220-240°C with textures corresponding to nematic thread. These terpolyestes are thermotropic liquid crystalline polymers having thermal stability value in the range of Ti (Temperature at which thermal decomposition is initiated) 370 - 390°C. Detailed description of the invention The process of the present invention has essentially the following steps: in situ scetylation of the monomers, hydroquinone and 8- (3 hydroxy phenyl) octanoic acid in presence cf acetylating agents such as excess phthalic anhydride, trifluoroacetic anhydride, acetic anhydride or chloroacetic anhydride and acidolysis polycondensation of the acetoxy derivative of the hydroxy acid and the diol with 2,6 naphthalene dicarboxylic acid by acidolysis polycondensation in presence of transesterfication catalysts such as magnesium acetate, antimony trioxide , lead acetate etc. at higher temperatures in the order of 240-280°C for 2-6 hrs in inert atmospheres. Polymerisation was further continued under reduced pressure of 1-3 mm of Hg at a temperature range of 260-2SOoC for a period of 1-6 hrs. This was followed by a postpolymerisation step carried out at a temperature in the range of 260-280°C under inert atmosphere for 24-72 hrs and a purification step involving soxhlet extraction using solvent mixtures such as acetone-methanol, acetone -methylethyl ketone , acetone -isopropanol mixtures etc. Theprocess for preparation of liquid crystalline poly(4-pheylene naphthalen -2,6- carboxylate -co-8 (3- oxyphenyl) octanoate)s, pol^4-phenylene,2-methoxynaphthalene-2,6-carboxylate-co-8(3-oxyphenyl)octanoate)s, poly(4-phenylehe,2-phenyl naphthalene-2.6-;arboxylate -co-8(3-oxyphenyl) octanoate)s, of formula I comprises in situ acetylation of the monomers, hydroquinone and 8-(3 hydroxy phenyl) octanoic acid in presence of acetylating agents such as excess phthalic anhydride, trifluoroacetic anhydride, chloroacetic anhydride or acetic anhydride and acidolysis polycondensation of the acetoxy derivative of the hydroxy acid and the diol with 2,6 naphthalene dicarboxylic acid by acidolysis polycondensation in presence of transesterfication catalysts such as magnesium acetate, antimony trioxide , lead acetate etc at higher temperatures using acetylating agents in presence of catalysts polymerisation in the presence of a high temperature solvent or without the solvent media ,with or without catalyst at a temperature range of 260-300°C for a period of about 6-24 hrs in the absence of a catalyst or in presence of transesterification catalysts such as acetates of lead, magnesium, cobalt, antimony etc. under reduced pressure for the efficient removal of acetic acid to effect higher molecular weight formation with post polymerisation effected at higher temperatures below the decomposition temperature for longer times and purification 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 60 ml polymerisation tube 0 20mol of 8 (3- hydroxy phenyl) octanoic acid,0.40mol of hydioquinone, and 0.40 mol of 2,6 naphthalene dicarboxylic acid were taken mixed with O.O8mol of acetic anhydride and 001 mmol of magnesium acetate were added and heated under slow stirring in a slow purge of nitrogen to 140 -150 °C and continued the heating for 1/2 hr Then temperature was increased tc 250-300 °C and continued for 2-3 hrs. Polymerisation was further continued at 0.01mm of Hg pressure for 1-2 hrs, Then the polymer was chipped out of the tube and purified by soxhlet extraction using acetone / isopropanol mixture for about 18 hrs and dried in an air oven at 60°C for about 3 hrs at reduced pressure. Example 2 In a 60 ml polymerisation tube O.lOmol of 8(3- hydroxyphenyl)octanoic acid ,0.45mol of hydroquinone, and 0.45 mol of 2,6 naphthalene dicarboxylic acid were taken mixed with O.O8mol of acetic anhydride and 0.01 mmol of magnesium acetate were added and heated under slow stirring in a slow purge of nitrogen to 140 °C and continued the heating for 1/2 hr. Then temperature was increased to 250-300 °C and continued for 2-3 hrs in presence of 3ml of high temperature solvent Dowtherm®. Polymerisation was further continued at 0.01mm of Hg pressure for 1-2 hrs. Then the polymer was chipped out of the tube and purified by soxhlet extraction using acetone / isopropanol mixture for about 18 hrs and dried in an air oven at 60°C for about 3 hrs at reduced pressure. Example 3 In a 60 ml polymerisation tube 0.2mol of 8 (3-hydroxyphenyl)octanoic acid ,0.40mol of 2 phenyl hydroquinone, and 0.40 mol of 2,6 naphthalene dicarboxylic acid were taken mixed with O.O8moI of acetic anhydride and 0.01 mmol of magnesium acetate were added and heated under slow stirring in a slow purge of nitrogen to 140 °C and continued the heating for 1/2 hr. Then temperature was increased to 250-300 °C and continued for 2-3 hrs. Polymerisation was further continued at 0.01mm of Hg pressure for 1-2 hrs. Then the polymer was chipped out of the tube and purified by soxhlet extraction using acetone / isopropanol mixture for about 18 hrs and dried in an air oven at 60°C for about 3 hrs at reduced pressure. Example 4 In a 60 ml polymerisation tube 0.20mol of 8(3-hydroxyphenyl) octanoic acid ,0.40mol of 2 methoxy hydroquinone, and 0.40 mol of 2,6 naphthalene dicarboxylic acid were taken mixed with O.O8moI of acetic anhydride and 0.01 mmol of magnesium acetate were added and heated under slow stirring in a slow purge of nitrogen to 140 °C and continued the heating for 1/2 hr. Then temperature was increased to 250-300 °C and continued for 2-3 hrs. in presence of 3ml of high temperature solvent Dowtherm® Polymerisation was further continued at 0.01mm of Hg pressure for 1-2 hrs. Then the polymer was chipped out of the tube and purified by soxhlet extraction using acetone / isopropanol mixture for about 18 hrs and dried in an air oven at 60°C for about 3 hrs at reduced pressure. The advantages of the present invention are the following: The present invention provides a process for the preparation of melt processable liquid crystalline terpolyester from 8(3-hydroxyphenyl)octanoic acid, hydroquinones and 2,6-naphthalene dicarboxylic acid. The liquid crystalline terpolyester obtained from 8(3-hydroxyphenyl ) octanoic acid, hydroquinones and 2,6-naphthalene dicarboxylic acid of formula I has a transition temperature @ 220-240°C which is lower than those (300°C) of the commercial liquid crystalline copolyester such as Vectra® and terpolyesters such as Xydar®. Hence, the liquid crystalline terpolyester obtained by the process of the present invention can be melt processed at a lower temperature than that of Yectra® and Xydar® and this may solve many of the processing problems associated with the existing commercial liquid crystalline polymers. The liquid crystalline terpolyesters obtained by the process of the present invention do not decompose before melting whereas poly(4-hydroxybenzoate) decomposes prior to melting. As the presentinvention described by the present process of preparation of liquid crystalline terpolyester from 8(3-hydroxyphenyl) octanoic acid, hydroquinones and 2,6-naphthalene dicarboxylic acid does not use a comonomer which is too expensive, the ccst of the liquid crystalline terpolyester obtained by the present process is rather low when compared to those of Vectra® and Xydar®. 8(3-hydroxyphenyl) octanoic acid .and hydroquinone, the comczamers used in the preparation of the terpolyester prepared by the process of the present invention, are comparatively cheaper. The process of the present invention has a step of post-polymerisation whereby a higher molecular weight is obtained so that the properties of the polymer are better. This terpciyester has got comparatively higher decomposition temperature, Ti of @ 370-390°C. The cost of the terpclyesters are comparatively less than that of the commercial copolyesters. It shows drastic reduction in viscosity due to nematic mesophase which is required for further processing by injection moling and extrusion. 1. We Claim: A process for the preparation of melt processible liquid crystalline terpolyesters of the general formula I, as shown below: (Formula Removed) where R is CI.C6H5.CH3CO.CH3 Formula said process comprising acetylating 8(3-hydroxyphenyl) octanoic acid and hydroquinone using an acetylating agent as defined herein, followed by acidolysis polycondensation in presence of a transesterification catalyst, such as herein described, at a temperature in the range of 240° - 280°C for a period of 6 - 24 hrs, under reduced pressure of 1 - 3m, of Hg for the efficient removal of acetic acid to effect higher molecular weight formation, post-polymerisation being effected at higher temperatures at the range of 250°C -300°C, in presence of high temperature solvent such as herein described, for a period of 42 - 72 hrs, followed by purification by soxhlet extraction using solvent mixtures selected from the group comprising of acetone-alcohol, acetone-methylethyl ketone to get desired terpolyesters. 2.A process as claimed in claim 1 wherein the acetylating agent used is selected from the group comprising of phthalic anhydride, trifluoroacetic anhydrided acetic anhydride, chloroacetic anhydride. 3.A process as claimed in claim 1 -2 wherein the transesterification catalyst used in the polycondensation step is selected from the group comprising of copper acetate, sodium acetate, magnesium acetate, lead acetate, calcium acetate, zince acetate, antimony triacetate. 4.A process as claimed in claims 1 - 3, wherein the high temperature solvent used is selected from the group comprising of dibenzyl benzene , its derivatives and mixture thereof. 5. A process as claimed in claims 1 - 4, wherein the obtained terpolyester has a decomposition temperature in the range of 370° - 390°C. 6. A process for the preparation of liquid crystalline terpolyesters substantially as described herein before and with reference to the foregoing examples.

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