LIQUID CRYSTAL COPOLYESTERS CONTAINING PHENYLHYDROQUINONE

Abstract: Liquid crystal copolyesters having excellent mechanical properties. The copolyesters are prepared from an aromatic dicarboxylic acid, phenylhydroquinone and a p-acyloxybenzoic acid.

Description: LIQUID CRYSTAL COPOLYESTERS CONTAINING PHENYLHYDROQUINONE Technical Field This invention relates to liquid crystal co¬ polyesters prepared from an aromatic dicarboxylic acid, a phenylhydroquinone and a p-acyloxybenzoic acid. When liquid crystal polyesters are calendared or subjected to other ther oforming operations the poly¬ esters are heated above their softening point . If the softening point of the polyester is high and close to the melting point of the polyester, the calendering or thermoforming operation can cause a substantial reduc¬ tion in the physical properties of the polyester. For many liquid crystal polyesters the softening point is only 10-30 C. below the melting point of the polyester and when these polyesters are heated above their soften¬ ing point a loss of the high strength and high stiffness characteristics of the polyesters occurs. It is highly desirable that liquid crystal polyesters have softening points substantially lower than their melting points so that the loss of desirable physical properties can be avoided during " calendaring or thermoforming. Background Art Belgian Patent 860,959 discloses polyesters prepared from terephthalic acid, 2-phenylhydroquinone . and up to 10 mole % , based on all repeating units of p-hydroxybenzoic acid.(PHB). This PHB content is equivalent to 22 mole % t based on the total moles of erepnt-naiic acid. These polyesters have softening points that aarree oonnllyy 1100°CC.. oorr lleessss b.elow their melting points. Disclosure of Invention This invention provides copolyesters that have surprisingly low softening points and in some instances the softening points are 100 C. and more below the melting points. The copolyesters of this invention are pre¬ pared from a dicarboxylic acid, which can be tereph- thalic acid or 2,6-naphthalenedicarboxylic acid or mix¬ tures thereof, phenylhydroquinone or a substituted phenylhydroquinone, and a p-acyloxybenzoic acid. This copolyester can be specifically defined as a copoly- ester having a fiber-forming molecular weight and havin the following radicals: wherein Rj is -• •'. ■ %-■ ••-- oorr I T. vIIII vT T or mixtures thereof , R 2 is hydrogen, chlorine , bromine or a monovalent alkyl radical having one to four carbon atoms , n is 1 , 2 or 3, and the range of is from 25 to 80 mole percent, based on the total moles of radical' (A) and radical (,C) combined. Preferably,R 2 is hydrogen and the range of radical (C) is from 30 to 6 mole percent and more pre¬ ferably the dicarboxylic acid is terephthalic acid. Radical (A) is the radical remaining after removal of the hydroxyl groups from the dicarboxylic acid, radical (B) is the radical remaining after remova OM 1. WI of the terminal hydrogen atoms from phenylhydroquinone or a substituted phenylhydroquinone, and radical (C) is the radical remaining after removal of the terminal hydroxyl group and acyl group from a p-acyloxybenzoic acid. The copolyesters of this invention can be pre¬ pared by an acidolysis procedure wherein terephthalic acid or 2, β -naphthalenedicarboxylic acid or combinations of terephthalic acid and 2,6-naphthalenedicarboxylic acid, a diacyl ester of phenylhydroquinone and a p-acyl¬ oxybenzoic acid are contacted at a temperature of 2β0 - 300°C. until most of the monocarboxylic acid has evolved. The temperature is then increased to 350-390 C. and the pressure is decreased to form a high molecular weight polymer. If the polymer solidifies prior to achieving a fiber-forming molecular weight, its molecular weight may be increased to a fiber-forming value by heating particles of the polymer in. an inert atmosphere or under reduced pressure at a temperature just below the sof- tening point of the polymer. The inherent viscosity of the copolyesters of this invention are at least 0.5 3 and preferably at least 1.0, measured at 25 C. using 0.1 gram of polymer per 100 ml. of a solvent composed by weight of 25 percent phenol, 35 percent tetrachloroethane, .and 40 percent p-chlorophenol. The molecular weights of the copolyes¬ ters of the invention are high enough to be in the fiber-forming range. The minimum fiber-forming molecu¬ lar weight of the polymer is about 5,000. In most cases the copolyester of the invention has a molecular weight above 8,000 and can have a molecular weight as high as 20,000. In some instances the molecular weight can range up to 2 3 000 or even higher. As a specific example, a mixture of 8.3 g (0.05 mole) terephthalic acid, 13-5 g (0.05 mole) of the diacetate ester of phenylhydroquinone and 9.0 g (0.05 mole) p-acetoxybenzoic acid was placed in a 100-ml. flask equipped with a stirrer, a short distil¬ lation column, and an inlet for nitrogen. The flask was evacuated and purged three times with nitrogen before being lowered into a metal bath maintained at 110°C. The mixture was heated under a nitrogen atmos- phere with stirring to a temperature of 260 C. at which point acetic acid began to distill rapidly from the flask. After the reaction mixture was heated with stir ring at this temperature for one-half hour, the temper¬ ature of the bath was increased to 300 C. for 30 minute and then to 36θ°C. A vacuum of 0.5 mm of mercury was then applied over a period of 10 minutes. After stirri was continued under 0.5 mm of mercury at 360 C. for about 10 minute's, a high melt viscosity, opaque, fibrou light tan polymer was obtained. The polymer had a mole cular weight -above 10,000 and an inherent viscosity of 2.9. The polymer can be melt-spun into a fiber. The above polymer was dried in an oven at 100°C. overnight and injection molded to give 2-1/2 x 3/8 x l/16-inch tensile bars and 5 x 1/2 x 1/8-inch flexure bars for testing. ASTM procedures were used for measuring the tensile strength and elongation (ASTM D1708), flexural modulus (ASTM D790), Izod impact strength (ASTM D256 Method A) , and heat deflection tem¬ perature (ASTM D648). Bars injection molded at 38θ°C. were smooth, clear and light amber. Molded flexure bars of this composition were thermoformed at 210°C. using a thermoforming die and a press. The bar was preheated at 210°C. for 30 seconds and easily formed within 20 seconds. . . O Other copolyesters within the scope of the invention containing 2,6-naphthalenedicarboxylic acid instead of all or part of the terephthalic acid can be prepared by a similar procedure but using slightly different reaction temperatures because of differences in melting, points. Crystalline melting points and softening points of copolyesters prepared from 2-phenyl-l,4-pheny- lene diacetate, terephthalic acid and p-acetoxybenzoic acid are listed below. The softening points (Ts) were determined with a Du Pont 9^1 Thermomechanical Analy¬ zer, using a 10-g weight on a tipped probe (0.025-in. diameter) and a scan rate of 10 C/min. The melting points (T ) were determined with a differential scan- ning calorimeter. TABLE 1 p-Acetoxybenzoic Acid, Mole 7. Ts, °C. Tm, °C. 0 331 341 5 325 335 10 311 317 . 20 283 299 30 227 309 50 202 325 60 185 373 70 188 379 80 335 379 Softening points and crystalline melting points of copolyesters prepared from 2-phenyl-l,4-pheny- lene diacetate, 2,6-naphthalenedicarboxylic acid, and p-acetoxybenzoic acid are as follows: TABLE 2 p-Acetoxybenzoic Acid, Mole % Ts , °C. Tm, a . 0 379 3 3i8 399 30 307 3 3<4 iβ6 50 232 NNoonn<e ϊ DDeeitected 80 246 NNoonn«e ϊ DDeeltected A wide variety of diesters of phenylhydro¬ quinone can be used to prepare the copolyesters of this invention. Examples of diesters include the dia¬ cetate, dipropionate, dibutyrate and dibenzoate. The diacetate and dipropionate are preferred. The p-acyloxybenzoic acid that provides radi¬ cal (C) in the copolyester of this invention correspond to the structure wherein R is phenyl or a monovalent alkyl radical of 1 to 8, preferably 1 to 4, carbon atoms. Examples of p- acyloxybenzoic acids include p-acetoxybenzoic acid, p- propionyloxybenzoic acid, p-butyryloxybenzoic acid, and p-phenoxybenzoic acid. Preferably, R is a monovalent alkyl radical having one carbon atom, in which case the p-acyloxybenzoic acid is p-acetoxybenzoic acid. The p-acyloxybenzoic acids can be prepared by conventional processes, such as reaction between p- hydroxybenzoic acid and a carboxylic anhydride, such as acetic anhydride. Other processes for preparation of the p-acyloxybenzoic aromatic carboxylic acids are well known in the art. The copolyesters of this invention can con¬ tain other divalent radicals in minor amounts. For example, minor amounts of other isomers of naphtha- lenedicarboxylic acid can be used. The copolyesters of this invention can contain nucleating agents, fillers, pigments, glass fibers, asbestos fibers, antioxidants, stabilizers, plasticizers, lubricants, fire-retardants, and other additives. OM fa WI

Claims: We Claim: 1. The copolyesters having the following divalent radicals: wherein R, is •o or mixtures thereof, R ls hydrogen, chlorine, bromine or a monovalent alkyl radical having one to four carbon atoms, n is 1, 2 or 3j characterized by the range of -o— S» ~ \ / •-"l£- being from 25 to 80 mole percent, based on the total moles of radical ( . A) and radical (C) combined. 2. The copolyesters of Claim 1 wherein the range of -o—» / • _c_ is from 30 to 65 mole percent 3. The copolyesters of Claim 1 wherein R, is 4. The copolyesters of Claim 1 wherein R is hydrogen. 5. A shaped article made from the copoly¬ ester of Claim 1.

Inventors: GEBEAU G, JACKSON W, KUHFUSS H
Applicants: EASTMAN KODAK CO
Application year: 1979
Main classification: C08G63
IPC codes: C08G63, D01F6