MELT PROCESSABLE OPTICALLY ANISOTROPIC POLYMERS

Abstract: Melt spinnable liquid crystal aromatic polyesters which are optically anisotropic in the melt phases and of fiber forming molecular weight comprise recurring moieties of the formulae in which the molar ratio of moiety II to moiety III is from 2:8 to 1:9.

Description: The present invention relates to linear polyesters, and, more particularly, it relates to melt processable optically anisotropic liquid crystal polyesters. Liquid crystal polyesters, or those which exhibit optical anisotropy in the melt phase, are well known in the art. Numerous patents describe such polyesters and some are, for example, generally described in the article by W. J. Jackson, Jr. appearing in the British Polymer Journal December 1980 entitled, "Liquid Crystal Polymers IV Liquid Crystalline Aromatic Polyesters". Some aromatic polyesters exhibit optical anisotropy in the molten state and can be melt spun into crystalline fibers which upon subsequent heat treatment further crystallize and substantially increase in tenacity. Such heat treated polyester fibers can be used for numerous purposes such as, for example, in tire cords and in other industrial and consumer products where high strength and low weight with its attendant economic and other advantages are desired. Specific applications for such type liquid crystal polyesters are as high strength reinforcements for numerous thermoplastic and thermosetting polymer materials. In addition to their use in the form of fibers, such polyesters can also be formed by molding, for example, injection molding, into a wide variety of substrates which will have outstanding stiffness and toughness and strength. EP-A-0072540 describes melt-anisotropic wholly aromatic polyesters, their production and fibers and films made from them. Those polyesters may be derived from an aromatic dicarboxylic acid, for example terephthalic acid, and a mixture of at least 80 mole % of hydroquinone mono substituted by an alkyl group having at least 5 carbon atoms or an aralkyl group having at least 7 carbon atoms and at most 20 mole % of a substituted hydroquinone other than the monosubstituted hydroquinone. Examples of the latter substituted hydroquinone. Examples of the latter substituted hydroquinones include methyl-, ethyl-, t-butyl-, chloro- and bromohydroquinones. In accordance with the present invention, improved low cost, high performance thermotropic polyesters, which are optically anisotropic in the melt, are manufactured and formed into fibers or molded into other useful articles using conventional thermoplastic polymer processing and forming technology. The invention provides a melt spinnable, liquid crystal polyester of fiber forming molecular weight and exhibiting optical anisotropy in the liquid phase comprising recurring moieties of the formula in which the molar ratio of moiety II to moiety III is from 2:8 to 1:9. The polymers according to the invention are formed by reacting polyester forming precursors of said moieties under polyester forming reaction conditions. Thus, they may be formed by solution polymerization, which is a preferred technique, or by melt or emulsion polymerization. They may be formed from the diacids, diacid halides, diols or esters by transesterification. In the preferred mode of practicing the invention, the polymers will be synthesized by solution polymerization techniques in which the precursor for moiety I is terephthaloyl chloride. The preferred precursor for moiety II is (1-phenylethyl) hydroquinone, and the preferred precursor for moiety III is methyl substituted hydroquinone. Upon synthesizing and recovering the polymer, the polymer may be formed into usefully shaped articles, as indicated above, by conventional techniques. Thus, for example, the polymer can be extruded and formed into pellets to provide a densified product which product may then be fed to another extruder and formed into various articles such as fibers by use of a spinneret or any suitable die to form films or sheets. In addition, the material may be injection molded into various configurations using conventional injection molding techniques. When formed into fibers, it is desirable to subject the fiber package to a heat treatment. This may be accomplished by simply heating the fiber package, with the fibers being in a relaxed condition, in an inert atmosphere, such as, for example, a flow of nitrogen to a sufficient temperature and for a sufficient period of time to increase the tenacity significantly. That is, increase the tenacity on the order of at least about 50%. Such a heat treatment is also desirable for other objects, e.g., sheets, films and molded articles. The specific reactants employed will be routinely selected by those skilled in the art, and it will be readily apparent to them that polymer grade reactants should be employed. Additionally, for most outstanding results, it is desirable that stoichiometric amounts of the reactants be employed. In passing, it should be mentioned that generally the mole ratio of moiety II to moiety III may vary over a wide range. As previously indicated, moiety II is preferably incorporated into the thermotropic polyester by employing (1-phenylethyl) hydroquinone as the monomer. Additionally, as indicated, such moiety may be incorporated into the polyester by using an ester derivative thereof. Such ester derivatives will be routinely manufactured by those skilled in the art employing (1-phenylethyl) hydroquinone as a starting material. An outstanding technique for synthesizing (1-phenylethyl) hydroquinone is to react styrene with hydroquinone in the presence of an organic diluent, preferably an ether, and in the presence of effective reaction stimulating amounts of a Lewis acid. The reaction is preferably conducted at approximately 135°C to about 145°C, and the crude product is purified by high vacuum batch distillation. In the preferred technique, the diluent will be tetraethyleneglycol dimethylether, that is, a material of the formula CH₃ (OCH₂CH₂)₄ OCH₃ which is commercially available under the registered Trade Mark "Tetraglyme". The preferred Lewis acid is para -toluene sulfonic acid, and, in this case, it is preferred to purify the crude (1-phenylethyl) hydroquinone product by distillation employing sodium hydrogen sulfite to neutralize the para -toluene sulfonic acid catalyst. Such a preferred process for the preparation of (1-phenylethyl) hydroquinone may be carried out as follows: Into a 50 liter three-necked round-bottom flask, there is charged 5 Kg (45.4 moles) of hydroquinone (Technical Grade Hydroquinone available from Eastman Chemical Products, Inc.). Additionally, there is charged 10 liters of Tetraglyme material and 60 grams (0.32 moles of para -toluene sulfonic acid monohydrate. A mechanical stirrer with a ground glass shaft is employed, and, while stirring slowly, the reagent mixture is warmed to about 140°C. While maintaining that temperature, 4.166 Kg (40 moles) of styrene is added over approximately a 90-minute period. During the addition of the styrene, a slight exothermic reaction sets in, and the temperature is maintained at approximately 140°C plus or minus about 5°C. After the styrene addition is finished, the reaction mixture is held at that temperature for approximately 5 hours after which time the heating and stirring is turned off and the mixture allowed to cool overnight. The crude product has the appearance of a heavy motor oil both in relative viscosity and color, and it is homogenous and free of suspended solids. The yield is about 19.316 Kg. The crude product is purified by high vacuum batch distillation employing a 12 liter flash reboiler with agitator and vacuum, a 121.92 cm x 5.08 cm (4 ft x 2") column packed with about 76.2 cm (30") of crimped wire mesh packing, a cooled refluxed condenser, a heat traced reflux splitter, receiver and associated piping. In a typical distillation, approximately 10 Kg of crude product is charged employing about 31 grams of sodium hydrogen sulfite to neutralize the para -toluene sulfonic acid catalyst. Distillation breakdown with one distillation is set forth in Table I. One redistillation of all the best fractions (fractions 4 & 5) easily yields a 96% plus pure (1-phenylethyl) hydroquinone product. (1-Phenylethyl) hydroquinone Distillation Charge Weight 10,000 grams Fraction # Weight Grams Temperature °C RFX/REB @ P Composition % Styrene % HQ/TG % PEHQ % DPE 1 150 122°/162° @ 400 20 80 -- - 2 3030 130°/163° @ 270 <2 95 <2 - 3 2225 124°/189° @ 50 -- 95 <3 - 4 925 174°/212° @ 3330 -- 7 93 - 5 2103 198°/249° @ 80 -- 4 94 6 142 205°/265° @ 90 -- -- 50 5 Residue 1378 ---------- -- -- 2 8 RFX = Reflux REB = Reboiler P = Pressure (Pa) HQ = Hydroquinone TG = Tetraglyme material PEHQ = (1-Phenylethyl)hydroquinone DPEHQ = Di(phenylethyl)hydroquinone - probably a mixture of 2,5-DPEHQ and 2,6-DPEHQ The preferred technique, alluded to above, for synthesizing the novel, melt processable, liquid crystal aromatic polyesters of the present invention is a solution polymerization technique, and, as also indicated above, it is preferred that the reactants be terephthaloyl chloride, (1-phenylethyl) hydroquinone and methyl substituted hydroquinone. Obviously, such reaction will be conducted in the presence of a hydrochloric acid trap. Suitable hydrochloric acid traps, or scavengers, are the organic bases, for example, aliphatic and aromatic amines, especially tertiary amines. The preferred trap is pyridine, and it is preferred to employ an excess, for example, up to about 50 percent molar excess of such material. The solvents employed for the solution polymerization will be routinely selected by those skilled in the art, but it is generally preferred to employ the low molecular weight chlorinated hydrocarbons, such as, for example, the fully or partially chlorinated C₁-C₃ alkanes like trichloromethane, trichloroethane with dichloromethane being preferred. The polymer may be synthesized employing a reactor equipped with both cooling and heating and provided with a reflux condenser. The reaction is generally conducted employing a moderate nitrogen flow blanket and substantially at atmospheric pressure. The polymer typically has a melting point of about 320°C and an inherent viscosity of about 0.6 to about 1.2 (dl per grams at a concentration of about 0.5 (grams per 100 ml) in a solvent of equal volumes of trifluoroacetic acid and methylene chloride. The thermotropic polymer, which is optically anisotropic in the melt phase, is capable of being melt spun into fibers, extruded into films or sheets and, as previously indicated, injection molded to form numerous substrates, for example, substrates which have utility as substrates for printed circuit boards. As previously indicated, such articles will be heat treated. In forming fibers, e.g. having a monofilament diameter of about 10 to 20 µm, the polymer is, first of all, formed into pellets by extruding the material as a rod followed by cooling and then chopping the rod into pellets of approximately 3-5 mm in size. Typical barrel temperatures in the extruder will be about 340°C. The pellets are then supplied to another conventional extruder and are formed by means of a spinneret into fibers which can be wound onto a package using conventional winding equipment. The packages are desirably formed by winding onto a metal package core. The packages, containing relaxed fibers, are then heat treated in nitrogen atmosphere at a temperature of about 302°C for about 22 hours (about 5 hours heat-up and about 17 hours hold period). As previously indicated, in accordance with this invention, melt spinnable, liquid crystal polyesters of fiber forming molecular weight and which are optically anisotropic in the melt contain recurring units of moiety III. The preferred reactant is methyl hydroquinone although, of course, other polyester forming moiety III precursors may be employed. While the proportion of moiety III may vary the molar ratio of moiety II to moiety III will be from 2:8 to 1:9 to produce heat treatable fibers having suitable tenacities; at molar ratios above about 2:8, the polymers generally have melting points which are too low (e.g., less than 300°C) for desired effective heat treatment. Heat treated fibers typically have the following properties: a tenacity of 10-15 grams per denier (calculated based on measurement of Instron break load using 12.7 mm gauge length at a rate of 2 mm per minute, and measurement of density and cross-sectional area); a tensile modulus of 250-500 grams per denier; and an elongation to break of 3-5%.

Claims: A melt spinnable liquid crystal polyester which is optically anisotropic in the melt phase and of fiber forming molecular weight comprising recurring moieties of formulae: in which the molar ratio of moiety II to moiety III is from 2:8 to 1:9. A process for forming a polyester according to claim 1, comprising reacting polyester forming precursors of said moieties under polyester forming reaction conditions. A process according to claim 2, wherein the precursor for moiety I is terephthaloyl chloride. A process according to claim 2 or claim 3, wherein the precursor for moiety II is (1-phenylethyl) hydroquinone. A polyester according to claim 1, wherein the polyester has a melting point of at least about 300°C. A heat treated fiber formed of the polyester of claim 1. A film formed of the polyester of claim 1. A molded article formed of the polyester of claim 1. The fiber of claim 6, wherein the fiber has a tenacity of at least 10 grams per denier.

Inventors: HUTCHINGS, DAVID ALAN, LEE, DAVID MICHAEL, SIELOFF, GLORIA MARY, WILLARD, GEORGE FREDERICK
Applicants: SIR S.P.A.
Application year: 1985
Main classification: C08G63
IPC codes: D01F6, C08G63, C07C39, C07C27, C07C67