POLYESTERS OF 4-CARBOXYBENZENEPROPIONIC ACID

Abstract: Polyesters of 4-carboxybenzenepropionic acid and unsubstituted aromatic diols have excellent processability, heat resistance, light stability and exceptionally high mechanical properties.

Description: POLYESTERS OF 4-CARBOXYBENZENEPROPIONIC ACID Technical Field This invention relates to new high molecular weight polyesters prepared from 4-carboxybenzenepro- pionic acid and unsubstituted aromatic diols. For commerical uses polyesters of improved mechanical properties are being sought, and in order to increase the mechanical properties it is usually neces¬ sary to increase the molecular weight of the polyesters. As the molecular weight is increased the melting point of the polyesters increases, resulting in polyesters that are difficult to process in present commercial equipment. To be useful commercially the polyesters must have excellent processability and excellent mech- anical properties. The polyesters must also be stable at elevated temperatures and for some uses good light stability is required. Background Art Heat stability is an important property for many polyester applications. For example, if a poly¬ ester is used close to an automobile engine or in an electronic apparatus in which the parts become heated by hot vacuum tubes, it is. necessary that the poly¬ ester be stable under these conditions. German Offenlegungesschrift 2,530,820 dis¬ closes polyesters that are prepared from 4-carboxy- benzene-oxyacetic acid and unsubstituted diols. These polyesters apparently have desirable properties, but the polyesters are not sufficiently stable at elevated temperatures. Also, light stability is an important property for many polyester uses. Some polyesters, such as the polyesters prepared from terephthalic acid and bis- phenol A diacetate, are severely discolored when exposed to light for long periods of time. OMPI &Tr. W1P0 ^ Disclosure of Invention The polyesters of this invention have excel lent mechanical properties and they can be processed in current commercial melt-processing equipment. Also these polyesters have better heat stability and light stability than prior art polyesters. The polyesters of this invention are prepare by polymerizing 4-carboxybenzenepropionic acid with a unsubstituted aromatic diol. When a linear unsubsti- tuted aromatic diol, such as hydroquinone, is used, th polyester is a liquid crystal polyester. When a non¬ linear unsubstituted aromatic diol, such as 4,4'-iso- propylidenediphenol, is used, the polyester is not liquid crystalline. Table I demonstrates the surprising improve¬ ment in heat stability that the polyesters of this in¬ vention have. In this table the heat or thermal stability of polyesters prepared by polymerizing 4-car boxybenzenepropionic acid with certain aromatic diols is compared with polyesters prepared by polymerizing 4-carboxybenzene oxyacetic acid and similar aromatic diols. Although 4-earboxybenzenepropionic acid differ from 4-carboxybenzene oxyacetic acid only by changing an oxygen atom to a-CH -group, a surprising increase in the heat or thermal stability is obtained by this slight change. Thermal stability of the polyesters in Table I was determined by thermogravimetric analyses (TGA) in nitrogen. The thermal properties of these polymers are summarized in Table I. The preparations of poly¬ esters 1, 3 and 5 are given in Examples 1, 4 and _5. Polyester 2 (I.V. 0.54) was similarly prepared but a melt temperature of 275°C. was used. Polyesters 4 and 6 were prepared by solid-state polymerization of pre- polymers (28θ°C, 0.1 mm) which had solidified in the melt at 300°C. O WI Polyester 1 of the invention is more thermally stable than polyester 2 of the prior art, polyester 3 is more stable than polyester 4, and polyester 5 is more stable than polyester 6. TABLE I THERMAL STABILITY Temperature Temperature at Which 10% at Which 50% A-Carboxybenzene- A-Carboxybenzene- Weight Loss Weight Loss Weight Loββ Polyesters propionlc Acid oxyacέtlc acid at A00°C % Occurs, °C Occura, *C 1 A,A'-l8oproρyli- dene diphenol 2.5 AA5 500 2 A,A*-Isopropyli- dene diphenol 5.0 A15 A65 3 Hydroquinone 1.0 A50 530 A Hydroquinone 13.0 390 A95 5 30 mole % tere- 0.0 A80 530 phthalic acid and hydroquinone 6 30 mole X tere- 2.0 A30 A95 The polyesters of this invention have an in¬ herent viscosity of at least 0.4 and preferably at least 0.8 and are prepared from 4-carboxybenzenepropionic acid and unsubstituted aromatic diols. The. acid portion of the polyesters can be modified with up to 50 mole percent of at least one aliphatic, alicyclic or aromatic dicarboxylic acid. These modifying acids include tere- phthalic acid, isophτj-halic acid, 2,6-naphthalenedicar- boxylic acid, cis or trans-l,4-cyclohexanedicarboxylic acid, 4,4'-oxydibenzoic acid, monochloroterephthalic acid, a dichloroterephthalic acid, methyl terephthalic acid, a dimethyl erephthalic acid and 4,4'-diphenyldi- carboxylic acid. The unsubstituted aromatic diol portion of the polyesters of this invention includes hydroquinone, 4,4'-isopropylidendiphenol, 4,4'-thiodiphenol, 4,4'- oxydiphenol, 4,4'-(2-norbornylidene) iphenol, 4,4'- (cyclohexylmethylene)diphenol, 4,4'-dihydroxybiphenyl, 1,4-naphthalenediol, 1,5-naphthalenediol and 2,β-naph- thalenediol. Also minor amounts of substituted hydroquin- ones such as chloro, bromo and methyl hydroquinone can be used so long as the thermal stability of the poly¬ esters of this invention is not adversely affected. The diacyl derivatives of the aromatic diols can be used to prepare the polyesters of this invention. The acetyl and propionyl derivatives are preferred, but the butyryl, isobutyryl, or benzoyl derivatives are examples of others which may also be used. By "unsub-r stituted," we mean that no group such as alkyl, alkoxy, or halogen is attached to an aromatic ring of the aro¬ matic diol. The preferred diols are hydroquinone and 4,4'-isopropylidenediphenol. A polyester of this invention can be prepared from 4-carboxybenzenepropionic acid, a diacyl ester of ' B UREAU OMPI y WIPO ; hydroquinone and a p-acyloxybenzoic acid and can be fined as a polyester having a fiber-forming molecula weight and having the following divalent radicals: (A) - — / •-CHsCHz-C- •=• (B) -0- ^ J and wherein the range o ra ca (C) is 10 to 90 mole pe cent, based on the sum of radicals (A) and (C). In preferred embodiment the range of radical ( . C) is fro 30 to 80 mole percent. The polymers of the invention can be made techniques such as by acidolysis of the aromatic dio diacetate with the 4-carboxybenzenepropionic acid. reactants are heated at about 260 C. until most of t monocarboxylic acid has evolved. The temperature of melt is then increased to about 325 C. (up to 360 C. the higher-melting compositions), a vacuum of about millimeter is applied, and stirring is continued unt a high-melt viscosity polymer is obtained. If the p mer solidifies, its molecular weight may be increase to a sufficient value by., heating particles of the po πier in an inert atmosphere or under reduced pressure at a temperature just below the softening point of t polymer. Tough films of the polymers are obtained b pressing or by extrusion. Molding plastics having very high impact strength and heat-deflection temper tures are obtained by injection molding at about _ 350°C. In addition to plastics, the polyesters of this invention can be fabricated to give other types shaped objects such as foamed plastics, fibers, ilm extruded shapes and coatings . The compositions of this invention also may contain nucleating agents, fibers, pigments, glass fibers, asbestos fibers, antioxidants, stabilizers, plasticizers, lubricants, and other addi- tives. This invention is further illustrated by the following examples. The polyesters prepared in these examples were tested and found to have excellent mech¬ anical properties . All inherent viscosities were determined at 25°C. in a 40/35/25 weight mixture of p-chlorophenol/ tetrachloroethane/phenol at a concentration of 0.1 g/100. ml. The melting points and glass transition tem¬ peratures were determined with a differential scanning calorimeter. The polyesters were dried in an oven at 100 C. overnight and injection molded to give 2-1/2 x 3/8 x 1/16-inch tensile bars and 5 x 1/2 x 1/8-inch flexure bars for testing. ASTM procedures were used for mea- suring the tensile strength and elongation (ASTM D1708), flexural modulus (ASTM D790), Izod impact strength (ASTM D256 Method A), and heat-deflection temperature (ASTM D648). EXAMPLE 1 This example illustrates the preparation of a polyester from 4-carboxybenzenepropIonic acid and bis- phenol A diacetate. A mixture of 77.6 g ( . 0.4 mole) 4-carboxyben- zenepropionic acid and 124.8 g O. mole) bisphenol A diacetate was placed in a 500 ml flask equipped with a stirrer, a short distillation column, and an inle.t 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 atmosphere with stirring to a temperature of 260°C. at which point acetic acid began to distill rapidly from the flask. After the reaction mixture w heated with stirring at this temperature for about on hour, the temperature of the bath was increased to 300°C. for 30 minutes and then to 325°C. A vacuum of 0.5 mm of mercury was applied over a period of 15 min utes. After stirring was continued under 0.5 mm of mercury at 350°C. for about 20 minutes, a high melt viscosity, clear, light a er polymer was obtained. The polymer had an inherent viscosity of 0.89 and a glass transition temperature of 147°C. A tough, crea able film can be pressed easily at 325°C. EXAMPLE 2 This example illustrates the preparation of copolyester using 50 mole percent of terephthalic aci The procedure described in Example 1 was us to prepare a copolymer from 50 mole percent 4-carboxy benzenepropionic acid, 50 mole percent terephthalic acid, and bisphenol A diacetate. The tough, light am polymer had an inherent viscosity of 0.70 and a glass transition temperature of 168°C. EXAMPLE 3 Using the procedure described in Example 1, polyester was prepared from 77-6 g (0.4 mole) 4-carbo benzenepropionic acid and 120.8 g (0.4 mole) 4,4'-t.hi diphenol diacetate. The polyester had an inherent vi cosity of 0.74. A tough, creasable film can be press easily at 325°C. EXAMPLE 4 Using the procedure described in Example 1, prepolymer was prepared from 19.4 g (0.1 mole) 4-car- boxybenzenepropionic acid and 22.2 g (0.1 mole) hydro quinone dipropionate. The prepolymer, which had solidified in the flask, was ground to pass a 20-mesh screen for subsequent solid-state polymerization. So state polymerization of the prepolymer was accomplish by heating the particles under reduced pressure (0.1 mm Hg) at 2δO°C. for four hours. The polyester had a melting point of 425°C. EXAMPLE 5 The procedure of Example 1 was used (except the vacuum was applied at 34θ°C. instead of 325°C.) to prepare a copolyester with 0.42 mole (70 mole per¬ cent) 4-carboxybenzenepropionic acid, 0.18 mole (30 mole percent) terephthalic acid, and 0.60 mole (100 mole percent) hydroquinone dipropionate. A high melt viscosity liquid crystalline insoluble copolyester with a melting point of 316 C. was obtained. EXAMPLE 6 The procedure of Example 5 was used to prepare a copolyester with 0.20 mole 4-carboxybenzenepropionic acid, 0.20 mole terephthalic acid, 0.20 mole hydroqui¬ none diacetate, and 0.20 mole bisphenol A diacetate. The copolyester had an inherent viscosity of 0.88. EXAMPLE 7 A mixture of 14.4 g. (0.08 mole) p-acetoxy- benzoic " acid,3.88 g. (0.02 mole) 4-carboxybenzenepro- pionic acid, and 4.44 g. (0.02 mole) hydroquinone dipropionate was placed in a 100-ml. flask equipped with a stirrer, a short distillation 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 atmosphere with stirring to a tem¬ perature of 260 C. at which point acetic acid began to distill rapidly from the flask. After the reaction mixture was heated with starring at this temperat.ure for about 1 hour, the temperature of the batch was increased to 300°C. for 30 minutes and then to 350 C. A vacuum of 0.5 mm of mercury was then applied over a period of 10 minutes. After stirring was continued under 0.5 mm of mercury at 35Q C. for about 10 minute a medium melt viscosity, opaque, fibrous, light tan polymer was obtained. A second polyester was prepared in a simila manner, except 4-carboxybenzeneoxyacetic acid was use in place of the 4-carboxybenzenepropionic acid in the first polyester and the final reaction temperature wa 340 C. to limit the considerable color formation. Ten mil films of both polyesters were press at temperatures ranging from 325 to 350 C. and were placed in a 150°C. forced air oven. Once a week the films were creased by hand. The number of weeks required for the film to break upon creasing was re¬ corded as heat stability. The following table sum- marizes the heat stability data for both polyesters. Heat Stability , Weeks to Polymer 1 20 ' >20 2 20 4 The polyesters of this invention also have improved light stability compared to similar polyeste prepared with aromatic dicarboxylic acids other than 4-carboxybenzenepropionic acid. A pressed film of a polyester prepared from this acid and bisphenol A diacetate turned only slightly yellow when exposed fo 35 hrs. (40 fading units) in a fadeometer containing a xenon lamp. A film of a similar polyester prepared with terephthalic acid and bisphenol A diacetate turned deep yellow at the same time in the test. IJU OM . . WI

Claims: Claims: 1. A high molecular weight polyester char¬ acterized by having been prepared from 4-carboxyben- zenepropionic acid and an unsubstituted aromatic diol. 2. A polyester according to Claim 1 wherein the acid portion of the polyester is modified with up to about 50 mole percent of an aliphatic, alicyclic or aromatic dicarboxylic acid. 3. A polyester according to Claim 2 wherein the modifying acid is selected from terephthalic acid, isophthaliσ acid, isophthalic acid, 2, ' 6-naphthalenedi- carboxylic acid, cis or trans-l,4-cyclohexanedicar- box lic acid, 4,4'-oxydibenzoic acid, monochlorotere¬ phthalic acid, a dichloroterephthalic acid, methyl terephthalic acid, a dimethylterephthalic acid and 4,4'- diphenyldicaroxylic acid. 4. A polyester according to Claim 1 wherein the unsubstituted aromatic diol is selected from hydro¬ quinone, 4,4'-isopropylidenediphenol, 4,4'-thiodiphenol, 4,4'-oxydiphenol, 4,4'-(2-norbornylidene)diphenol, 4,4'- (c clohexylmethylene)diphenol, 4,4'-dihydroxybipheny1, 1,4-naphthalenediol, 1,5-naphnaphthalenediol and 2,6- naphthalenediol. 5. A polyester according to Claim 2 wherein the unsubstituted aromatic diols are selected from hydroquinone, 4,4 f -isopropylidenediphe.nol, 4,4'-thio¬ diphenol, 4,4'-oxydiphenol, 4,4'-(2-norbornylidene)- diphenol, 4, '-(cyclohexyl ethylene)diphenol, 4,4'- dihydroxybiphenyl, 1,4-naphthalenediol, 1,5-naphth- alenediol and 2,6-naphthalenediol. 6. A high molecular weight polyester h_aving the following divalent radicals : 'BU E U OMPI (A) -8 - W V-CHsCHa-fr (B) -< • .-0- and -% (C) -o→. \ / V?- wherein the range of radical (C) is 10 to 90 mole per cent, based on the sum of radicals (A) and (C).

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