IMPROVED PROCESS FOR FORMING THERMALLY STABLE THERMOTROPIC LIQUID CRYSTALLINE POLYESTERS OF PREDETERMINED CHAIN LENGTH

Abstract: An improved polymerisation process is provided for the formation of a polyester which is capable of forming an anisotropic melt phase and which optionally may include amide linkages. An approximately 0.4 to 3 percent molar excess of aromatic dicarboxylic acid monomer (e.g. tereph­ thalic acid) and/or an esterified derivative thereof is provided in the polymerisation zone during the polymerisation reac­ tion. Such monomer imparts dicarboxyaryl units to the interior of the resulting polymer chains and causes the polymer chains to terminate in carboxylic acid end groups and/or an esterified derivative thereof wherein the polymer chains achieve a predetermined average chain length through the depletion of other monomers present in the polymerisa­ tion zone. The resulting polyester unlike the usual product of the prior art is substantially incapable of additional chain growth upon subsequent heating and accordingly may be relied upon to maintain a substantially constant viscosity dur­ ing melt processing regardless of the duration of heating.

Description: The invention relates to a process for the production of a thermally stable thermotropic liquid crystalline polyester of predetermined chain length. It has been disclosed that certain polyesters may be formed which exhibit melt anisotropy. Such polymers commonly are referred to as being thermotropic liquid crystalline polymers. See, for instance, (a) Polyester X7G-A Self Reinforced Thermoplastic, by W. J. Jackson, Jr., H. F. Kuhfuss and T. F. Gray, Jr. , 30th Anniversary Technical Conference, 1975, Reinforced Plastics Composites Institute, The Society of the Plastics Industry, Inc., Section 17-D, pages 1-4; (b) BE-A-828,935 and 828,936; (c) NL-A-7505551; (d) DE-C-2520819, 2520820, 2722120, 2834535, 2834536 and 2834537; (e) JP-A-43-223; 2132-116; 3017-692 and 3021-293; (f) US-A-3,991,013; 3,991,014; 4,057,597; 4,066,620; 4,067,852; 4,075,262; 4,083,829; 4,093,595; 4,118,372; 4,130,545; 4,130,702; 4,146,702; 4,153,779; 4,156,070; 4,159,365; 4,161,470; 4,169,933; 4,181,792; 4,183,895; 4,184,996; 4,188,476; 4,201,856; 4,219,461; 4,224,433; 4,266,970; 4,230,817; 4,232,143; 4,232,144; 4,238,598; 4,238,599; 4,238,600; 4,242,496; 4,245,082; 4,245,084; 4,247,514; 4,256,624; 4,265,802; 4,207,304; 4,269,965; 4,272,625; 4,279,803; 4,284,757; 4,285,852; 4,287,332; 4,294,955; 4,299,756; 4,311,824; 4,314,073; 4,318,841; 4,318,842; 4,330,457; 4,332,759; 4,333,907; 4,335,232; 4,337,190; 4,337,191; 4,339,375; 4,341,688; 4,346,208; 4,347,349; 4,351,917; 4,351,918; 4,355,132; 4,355,133; 4,355,134; 4,359,569; 4,360,658; 4,362,777; 4,370,466; 4,371,660; 4,374,288; 4,375,530; 4,381,389; 4,348,016; 4,393,191 and 4,394,498; (g) GB-A-2,002,404; (h) GB-A-1,568,541 and (i) EP-A-24,499 and 45,499. Amide groups and/or carbonate groups additionally may be present in the polyesters which exhibit melt anisotropy. The thermotropic liquid crystalline polymers of the prior art are formed by techniques whereby the requisite reactive groups which form ester-groups along the polymer chain are carefully reacted so as to provide a stoichiometric balance of reactive groups. For instance, if a relatively volatile monomer, such as hydroquinone or hydroquinone diacetate is employed as a reactant, an excess of this monomer sometimes is provided to compensate for the quantity of this reactant which is evolved and lost by volatilisation through the use of the specific polymerisation conditions selected. When the various ester-forming monomers are provided and react with each other under stoichiometrically balanced conditions, a polymer is produced having the random presence of the requisite ester-forming groups at the ends of the polymer chain. These end groups unless otherwise end capped in a further reaction step have the propensity upon subsequent thermal processing to react with each other and to cause the polymer chains to continue to grow in length. The thermal processing of such polymers to increase the molecular weight in the solid state is disclosed, for example, in US-A-3,975,487; 4,183,895 and 4,247,514. The continued polymerisation via a condensation reaction results in the simultaneous evolution or off-gassing of relatively small molecular by-products and an elevation in the melt viscosity of the resulting polymer upon any subsequent melt processing. Such increase in melt viscosity may require the selection of different melt processing conditions at different points in time as the average chain length increases. For instance, it may be desirable to modify the injection moulding conditions when forming moulded articles from the resulting anisotropic melt-forming polyester. Accordingly, the melt processing of such polymers may require the continued or periodic monitoring of the molten polymer viscosity and the adjustment of melt processing conditions in an effort to yield uniform moulded products if the molten polymer is provided at an elevated temperature for an extended period of time. Additionally, the melt devolatilisation of previously formed thermotropic liquid crystalline polymers of the prior art is desirable to remove substantial quantities of void-forming volatile materials contained therein. However, if such devolatilisation is practised for a sufficient period of time so as substantially to remove such volatiles, a continued molecular weight increase also will occur. It has been found that in a process for the formation within a polymerisation zone of a polyester which is capable of forming an anisotropic melt phase through a polymerisation reaction of ester-forming monomers to form a polymer having recurring moieties and that consists essentially of moieties I and II, which optionally may include substituents of at least some of the hydrogen atoms present upon an aromatic ring, wherein: with the said optional substituents if present being selected from alkyl groups of 1to 4 carbon atoms, alkoxy groups of 1 to 4 carbon atoms, halogen, phenyl and mixtures of the foregoing, and wherein the said polymer comprises 10 to 90 mole percent of moiety I and 10 to 90 mole percent of moiety II, improved results are achieved by providing in the polymerisation zone during the polymerisation reaction a 0.25 to 4 percent molar excess of aromatic dicarboxylic acid monomer and/or an esterified derivative thereof which during the polymerisation reaction imparts dicarboxyaryl units to the interior of the polymer chains of the resulting polymer and causes the polymer chains to terminate in carboxylic acid end groups and/or an esterified derivative thereof. By this process the polymer chains achieve a predetermined average chain length through the depletion of other monomers present in the polymerisation zone to yield a polyester product which is substantially incapable of additional chain growth upon subsequent heating. A polyester formed in accordance with the process of the invention is provided which is capable of forming an anisotropic melt phase, is substantially incapable of further chain growth upon heating, and possesses polymer chains which terminate substantially exclusively in carboxylic acid end groups and/or an esterified derivative thereof. The invention provides a number of important advantages among which are the following: The invention provides a thermally stable thermotropic liquid crystalline polyester of predetermined chain length. The invention provides a thermally stable thermotropic liquid crystalline polyester which is particularly suited for melt processing to form substantially uniform moulded articles on a consistent basis. The present invention provides a thermotropic liquid crystalline polymer which will generate a significantly reduced amount of volatile by-products during further melt processing. The invention provides a thermotropic liquid crystalline polymer which is capable of undergoing vigorous melt devolatilisation without concomitantly producing an excessive polymer chain growth and a significant change in the melt viscosity of the resulting polymer. The invention provides a thermally stable polyester which is capable of forming a liquid crystalline melt phase without the need of employing a conventional end-capping reaction of a previously-formed polymer. Other advantages of the invention will be apparent to those skilled in the art from the following detailed description. Crystalline polymer exhibits optical anisotropy in the melt. The anisotropic character of the polymer melt may be confirmed by conventional polarised light techniques whereby crossed-polarisers are utilised. More specifically, the anisotropic nature of the melt phase may conveniently be confirmed by the use of a Leitz polorising microscope at a magnification of 40 X with the sample on a Leitz hot stage and under a nitrogen atmosphere. The amount of light transmitted changes when the sample is forced to flow; however, the sample is optically anisotropic even in the static state. On the contrary typical melt processable polymers do not transmit light to any substantial degree when examined under quiescent conditions and are isotropic in nature. When such polymer is heated in an inert atmosphere (e.g. nitrogen or argon) for 30 minutes while at a temperature of 340°C., its weight average molecular weight preferably increases no more than 15%. Any of the polyester-forming monomers which are capable of forming the polyester which exhibits an optically anisotropic melt phase may be employed in the improved process of the present invention. Minor quantities of carbonate-forming monomers may be included provided they do not adversely influence the ability of the resulting polyester to exhibit an optically anisotropic melt phase. In a preferred embodiment the resulting polymer is wholly aromatic in the sense that each moiety present therein contributes at least one aromatic ring. Monomers for selection when forming the polyester in accordance with the process of the present invention are those which impart recurring moieties to the polymer chain where Ar is a combination of 1,4-phenylene or 2,6-naphthalene. Accordingly the moieties are 4-oxybenzoyl moieties and 6-oxy-2-naphthoyl moieties in such instances. Such monomers are inherently stoichiometrically balanced, since they contain precisely the correct quantity of esterforming reactant groups. The aromatic ring or rings present optionally may include substitution of at least some of the hydrogen atoms present thereon. Such substitution may be selected from an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen (e.g. Cl, Br, I), phenyl and mixtures of the foregoing. Particularly preferred moieties may be derived from 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. Representative ring substituted moieties include 2-chloro-4-hydroxybenzoic acid, 2,3-dichloro-4-hydroxybenzoic acid, 3,5-dichloro-4-hydroxybenzoic acid, 2,5-dichloro-4-hydroxybenzoic acid, 3-bromo-4-hydroxybenzoic acid, 3-methyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, 2,6-dimetbyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoic acid, 3,5-dimethoxy-4-hydroxybenzoic acid, 3-phenyl-4-hydroxybenzoic acid, 2-phenyl-4-hydroxybenzoic acid, 6-hydroxy-5-chloro-2-naphtholc acid, 6-hydroxy-5-methyl-2-naphthoic acid, 6-hydroxy-5-methoxy-2-naphthoic acid, 6-hydroxy-4,7-dichloro-2-chloro-2-naphthoic acid. In accordance with the concept of the present invention all ester-forming monomers are added to the polymerisation zone in carefully measured quantities so that during the course of the polymerisation there is provided a 0.25 to 4 percent molar excess of aromatic dicarboxylic acid monomer and/or an esterified derivative thereof. In a preferred embodiment the aromatic dicarboxylic acid is provided during the course of the polymerisation reaction in a molar excess of 0.5 to 3 pecent. It is essential that this molar excess of aromatic dicarboxylic acid monomer (and/or an esterified derivative thereof) be provided during the polymerisation reaction over and above the other monomer quantities which are sufficient to provide a stoichiometric balance between all carboxylic acid reactive groups (and/or an esterified derivative thereof) and the hydroxyl reactive groups (and/or an esterified derivative thereof). Preferred aromatic dicarboxylic acid monomers which are provided in the specified molar excess are terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 2-phenylterephthalic acid; 4,4′-bibenzoic acid, etc. During the course of the polymerisation reaction in the process of the present invention dicarboxyaryl units derived from such molar excess of aromatic dicarboxylic acid monomer and/or an esterified derivative thereof are incorporated into the interior of the polymer chains of the resulting polymer and cause the polymer chains to terminate in carboxylic acid groups and/or an esterified derivative thereof. As the polymerisation reaction progresses the other monomers present in the polymerisation zone are fully depleted. The average polymer chain length achieved is directly controlled by the molar excess quantity of aromatic dicarboxylic acid monomer and/or its esterified derivative provided inthe polymerisation zone during the course of the polymerisation reaction. As the molar excess quantity of dicarboxylic acid monomer and/or is esterified derivative increases within the range specified, the average polymer chain length decreases. As the molar excess quantity of dicarboxylic acid monomer and/or its esterified derivative decreases within the range specified, the average polymer chain length increases. A polymer product of predetermined average chain length is produced by the process of the present invention through the selection of the specific molar excess utilised. Such average chain length may be conveniently evidenced by the inherent viscosity of the resulting polymer. In all instances the polymer chains of the resulting thermotropic liquid crystalline polyester terminate in carboxylic acid end groups and/or an esterified derivative thereof. Such product is thermally stable since the like end groups are substantially incapable of additional polymer chain growth upon subsequent heating. The polyester of the present invention may be formed by a variety of ester-forming techniques whereby organic monomer compounds possessing functional groups which upon condensation form the requisite recurring moieties are reacted. For instance, the functional groups of the organic monomer compounds may be carboxylic acid groups, hydroxyl groups, ester groups (e.g. acyloxy groups), acid halides. The organic monomer compounds may be reacted in the absence of a heat exchange fluid via a melt acidolysis procedure. They, accordingly, may be heated initially to form alargely melt solution of the reactants wherein some reactants such as terephthalic acid initially are present to some degree as solids. Low levels of terephthalic acid may dissolve under such circumstances. The polymer product sometimes is suspended therein as solid polymer particles. A vacuum may be applied to facilitate removal of volatiles formed during the final stage of the condensation (e.g., acetic acid or water) and otherwise to expedite the polymerisation. In our US-A-4,067,852 is described a slurry polymerisation process which may be employed to form the polyester of the present invention wehrein the solid product is suspended in a heat exchange medium. When employing either the melt acidolysis procedure or the slurry procedure of US-A-4,067,852 the monomer reactants from which the polymer moieties are derived which would otherwise include a hydroxyl preferably are preliminarily esterified. They preferably are provided as lower acyl esters of 2 to 4 carbon atoms. Preferably the acetate esters of such monomers which would otherwise include a hydroxyl group are provided. Examples of such reactants are 6-acetoxy-2-naphthoic acid and 4-acetoxybenzoic acid. Alternatively any monomers which impart carboxyaryl units to the resulting polymer which chain such as the aromatic dicarboxylic acid monomer which is provided in molar excess may be provided initially in an esterified form. For instance, they may first be reacted with an aromatic monohydroxy compound such as phenol, m-cresol or p-cresol, as described, for example in US-A-4,333,907. Examples of such reactants include phenyl p-hydroxybenzoate. In a preferred embodiment the carboxylic acid groups of the reactants are non-esterified. Representative catalysts which optionally may be employed in either the melt acidolysis procedure or in the procedure of US-A-4,067,852 include dialkyl tin oxide (e.g., dibutyl tin oxide), diaryl tin oxide, titanium dioxide, alkoxy titanium silicates, titanium alkoxides, alkali and alkaline earth metal salts of carboxylic acids, the gaseous acid catalyst such as Lewis acids (e.g. BF₃), hydrogen halides (e.g. HCl). The quantity of catalyst utilised typically is 0.001 to 1 percent by weight based upon the total monomer weight, and most commonly 0.01 to 0.2 percent by weight. The polymerisation procedures of our US-A-4,393,191 and US-A-4421908 (= EP-A-88546) and 4429105 (= EP-A-117086) also are suitable for use when carrying out the process of the present invention. In a particularly preferred embodiment a polyester of our US-A-4,161,470 is produced in a modified form in accordance with the concept of the present invention. In such embodiment wherein a process is carried out for the formation within a polymerisation zone of a wholly aromatic polyester which is capable of forming an anisotropic melt phase through a polymerisation reaction of ester-forming monomers to form a polymer which consists essentially of moieties I and II wherein: wherein said polyester comprises 10 to 90 mole percent (e.g. 25 to 45 mole percent) of moiety I and 10 to 90 mole percent (e.g. 55 to 75 mole percent) of moiety II. The thermotropic liquid crystalline polyesters of the present invention commonly form an anisotropic melt at a temperature below 400°C., and preferably at a temperature below 300°C. The polymeric product of the present invention tends to be substantially insoluble in all common polyester solvents, such as hexafluoroisopropanol and o-chlorophenol, and accordingly is not susceptible to solution processing. It can be readily processed by common melt processing techniques. Most compositions are soluble in pentafluorophenol to at least a slight degree. The wholly aromatic polyester of the present invention commonly exhibits a weight average molecular weight of 4,000 to 50,000, and preferably 6,000 to 30,000. Such molecular weight may be determined by standard gel permeation chromatography. For instance, in a typical test approximately 150 microlitres of a 0.1 percent by weight polymer solution in a solvent consisting of a 1: 1 mixture on a volume basis of pentafluorophenol and hexafluoroisopropanol are introduced into the gel permeation chromatography equipment consisting of a main control unit (e.g. Waters liquid chromatograph Model No. 201), four columns containing porous silica particles (e.g. du Pont SE 4000, du Pont SE 1000, du Pont SE 100 and Waters 60 Angstrom Microporasil), and a laser light scattering units (e.g. Chromatix KMX6) at ambient temperature. Typical melt processable anisotropic melt-forming polymers commonly show a retention time distribution in the range of 20 to 50 minutes. The polyester additionally commonly exhibits an inherent viscosity (i.e. I.V.) of at least 0.6 dl./g. and preferably at least 1.0 dl./g. (e.g., 1.0 to 10.0 dl./g. or more) when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C. In a particularly preferred embodiment the polyester of the present invention exhibits an inherent viscosity in the range of 1.5 to 8.0 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C. Alternatively, the inherent viscosity of the polyester may be determined while dissolved in a 1: 1 solution of pentafluorophenol/hexafluoroisopropanol in a concentration of 0.1 percent (W/V) at 25°C. This alternative technique offers the possibility of automation while operating at room temperature; however, it tends to yield numerical values which are higher than those obtained with a 0.1 percent solution in pentafluorophenol at 60°. For instance, such values with the mixed solvent may be of the order of approximately 10 percent higher than those obtained with pentafluorophenol at 60°C. The polyester of the present invention preferably also exhibits a melt viscosity in the range of 10 to 10,000 poise (1 to 1,000 Pa · s), preferably 50 to 3,000 poise (5 to 300 Pa · s), at 300°C., and a shear rate of 1.00 sec.⁻¹. Such melt viscosity may be determined by standard techniques using an Instron capillary rheometer having a capillary which measures inches 4 inches (10.16 cm) in lengt and has an inner diameter of 30 mils (0.76 mm). The polymeric product of the present invention is capable of withstanding vigorous melt devolatilisation following its formation to eliminate entrained gaseous by-products from the preceding polymerisation reaction. Suitable vigorous devolatilisation processing conditions can, for instance, be carried out for 10 minutes or more at a temperature above the polymer melting temperature (e.g. at approximately 320°C. or above) while under a reduced pressure of approximately 1 Torr (133 Pa) with vigorous agitation. The molecular weight of the polymer does not change to any substantial degree during such procedure nor does it change to any substantial degree during any subsequent melt processing step even if prolonged. The substantially complete removal of such gaseous by-product as well as the substantial non-generation of the same during subsequent melt processing facilitates the formation of quality moulded articles in the substantial absence of deleterious voids caused by off-gassing. Accordingly, high quality moulded articles may be consistently formed from the product of the present invention on a reliable and readily reproducible basis. The product of the present invention, because of its thermal stability, is particularly suited for the formation of moulded articles on a reliable and readily reproducible basis. The product is capable of undergoing vigorous melt devolatilisation. Example I It was desired to produce a thermally stable wholly aromatic polyester which is capable of forming an anisotrophic melt phase, and has a predetermined average chain length which is evidenced by an inherent viscosity of approximately 2.5 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C. To a 50 gallon (189.25 litre) reactor equipped with a sealed anchor stirrer, gas inlet tube and distillation head connected to a condenser were added at room temperature (i.e. approximately 25°C.) the following: (a) 115 pounds (52.2 kg) of 6-acetoxy-2-naphthoic acid (227 mole). (b) 131 pounds (59.5 kg) of 4-acetoxybenzoic acid (330 mole), (c) 3.891 pounds (1.766 kg) of terephthalic acid (10.6 mole), and (d) 6.98 grams of potassium acetate catalyst. It can be calculated that a molar excess of 1.87 percent of terephthalic acid monomer was provided in the reactor. More specifically, the 6-acetoxy-2-naphthoic acid and 4-acetoxybenzoic acid reactants were inherently stoichiometrically balanced since each provided the required carboxylic acid and acetoxy ester-forming reactant groups in an identically quantity. Accordingly, the terephthalic acid monomer served as an aromatic dicarboxylic acid monomer and provided the ester-forming carboxylic acid groups in a stoichiometric excess beyond the stoichiometric balance which existed with respect to the other monomers present. The reactor and its contents were thoroughly purged of oxygen by evactuating and refilling with nitrogen three times, and hot oil at a temperature of 220°C. was next caused to flow through the jacket of the reactor whose contents were thus heated to 203°C, and were maintained at that temperature of 83 minutes. In 15 minute increments the contents of the reactor were next heated to the following temperatures: 213°C., 219°C., 232°C., 248°C., 261°C., 274°C,, 289°C. and 303°C. Subsequently the contents of the reactor were heated to 325°C. over a period of 75 minutes and were maintained at that temperature. When the reactants reached 220°C., it was observed that the production of the acetic acid by-product of the polymerisation reaction had commenced. When the reactant temperature reached 325°C. during the above-identified heating schedule, the rate of acetic acid production during a 15 minute period had slowed to approximately 0.5 pound (0.227 kg) and a vacuum of 8 mm. Hg (1066 Pa) was applied to the reactants while heating was continued. Such heating under vacuum continued for 90 minutes. The vacuum next was broken and the molten polymer product was discharged through a 1 8 inch (3.55 mm) three-hole die, immersed in water to form solidified strands, and was pelletised. Approximately 150 pounds (68.1 kg) of the wholly aromatic polyester product were obtained. The chains of the resulting polymer included 1,4-dicarboxyphenylne units at interior locations along the length of the polymer chains and terminated in carboxylic acid end groups. When the polymer was heated in either the melt or in the solid phase, no further polymerisation or chain growth was observed. The inherent viscosity (I.V.) of the polymer product was found to be 2.24 dl./g. as determined in a pentafluorophenol solution of 0.1 percent by weight concentration at 60°C. in accordance with the equation: where c = concentration of solution (0.1 percent by weight), and η rel = relative viscosity. The weight average molecular weight of the polymer product was approximately 17,000. When the polymer was subjected to differential scanning calorimetry (20°C./min. heating rate), it exhibited a melt endotherm peak at 240°C. The polymer melt was optically anisotropic and exhibited a melt viscosity of approximately 140 poise (14 Pa · S) at 300°C. and at a shear rate of 100 sec.⁻¹. Example II Example I was substantially repeated with the exceptions indicated below. It was desired to produce a thermally stable wholly aromatic polyester of a shorter predetermined average chain length than was produced in Example I as evidenced by an inherent viscosity of approximately 1.8 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C. This was accomplished by providing a greater concentration of terephthalic acid in the reactor. To the reactor were added the following: (a) 115 pounds (52.2 kg) of 6-acetoxy-2-naphthoic acid (227 mole), (b) 130.2 pounds (59.1 kg) of 4-acetoxybenzoic acid (328 mole), (c) 4.46 pounds (2.02 kg) of terephthalic acid (12.2 mole), and (d) 6.98 grams of potassium acetate catalyst. It can be calculated that a molar excess of 2. 15 percent of terephthalic acid monomer was provided in the reactor. The contents of the reactor were heated to 208°C. over a period of 118 minutes. In 15 minute increments the contents of the reactor were next heated to the following temperatures: 213°C., 220°C., 234°C., 246°C., 259°C., 273°C., 290°C. and 303°C. The contents of the reactor were next heated to 325°C. over a period of 47 minutes and were maintained at that temperature. The inherent viscosity of the polymer product was found to be 1.6 dl./g. as determined in a pentafluorophenol solution of 0.1 percent by weight concentration at 60°C. The weight average molecular weight of the polymer product was approximately 9,700. When the polymer was subjected to differential scanning calorimetry (20°C/min. heating rate), it exhibited a melt endotherm peak at 236°C. The polymer melt was optically anisotropic and exhibited a melt viscosity of approximately 50 poise (5 Pa · s) at 300°C. and at a shear rate of 100 sec.⁻¹.

Claims: 1. A process for the formation within a polymerisation zone of a polyester which is capable of forming an anisotropic melt phase through a polymerisation reaction of ester-forming monomers to form a polymer having recurring moieties and that consists essentially of moieties I and II, which optionally may include substituents of at least some of the hydrogen atoms present upon an aromatic ring, wherein: with the said optional substituents if present being selected from alkyl groups of 1 to 4 carbon atoms, alkoxy groups of 1 to 4 carbon atoms, halogen, phenyl and mixtures of the foregoing, and wherein the said polymer comprises 10 to 90 mole percent of moiety I and 10 to 90 mole percent of moiety II, characterised in that there is provided in the polymerisation zone during the said polymerisation reaction a 0.25 to 4 percent molar excess of aromatic dicarboxylic acid monomer and/or an esterified derivative thereof which during the polymerisation reaction imparts dicarboxyaryl units to the interior of the polymer chains of the resulting polymer and causes the polymer chains to terminate in carboxylic acid end groups and/or an esterified derivative thereof. 2. A process in accordance with claim 1 wherein the polymerisation reaction is carried out in the melt. 3. A process in accordance with claim 1 wherein the polymerisation reaction is carried out while the monomers are suspended as a slurry. 4. A process in accordance with any of claims 1-3 wherein any monomer present in the polymerisation zone which would otherwise include a hydroxyl group is provided as a lower acyl ester of 2 to 4 carbon atoms. 5. A process in accordance with claim 4 wherein the lower acyl ester is an acetate ester. 6. A process in accordance with any of claims 1-5 wherein any monomer present in the reaction zone which yields carboxyaryl units in the polymer chains is provided with its carboxylic acid group(s) in a non-esterified form and yields a product wherein the polymer chains terminate in carboxylic acid groups. 7. A process in accordance with any of claims 1-6 wherein the said aromatic dicarboxylic acid monomer which is provided in a molar excess is selected from terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 2-phenylterephthalic acid, 4,4′-dibenzoic acid and mixtures of the foregoing. 8. A process in accordance with any of claims 1-7 wherein said aromatic dicarboxylic acid monomer and/or an esterified derivative thereof is provided in the polymerisation zone in a molar excess of 0.5 to 3 percent. 9. A process in accordance with any of claims 1-8 wherein the said polyester product exhibits an inherent viscosity of 1.0 to 10.0 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C. 10. A process in accordance with any of claims 1-9 wherein the said polymer comprises 25 to 45 mole percent of moiety I and 55 to 75 mole percent of moiety II.

Inventors: YOON, HYUN-NAM
Applicants: CELANESE CORPORATION
Application year: 1984
Main classification: C08G63
IPC codes: C08G63, C08G69, C08G18