LIQUID CRYSTAL COPOLYESTERS

Abstract: Liquid crystal copolyesters having melting points low enough to allow the copolyesters to be melt-processed in conventional equipment. The copolyesters are prepared from terephthalic acid, 2,6-naphthalenedicarboxylic acid, a diacyl ester of hydroquinone and a diacyl ester of resorcinol and contain the following divalent radicals:

Description: IQUID CRYSTAL COPOLYESTERS Technical Field This invention relates to liquid crystal co- polyesters having the high mechanical properties of liquid crystal copolyesters and melting points low enough to allow the copolyesters to be melt-processed into useful articles using commercially available equipment. Background of the Invention Liquid crystal cop'olyesters that are all-aro¬ matic have excellent mechanical properties. Examples of these , polyesters are the copolyesters prepared from terephthalic acid, 2,6-naphthalenedicarboxylic acid, hydroquinone and resorcinol. U.S. Patents 3,lβ0,β02 and 3,778,410 describe processes that can be used to ' prepare these copolyesters. It has been difficult to use these copolyesters because the melting points of the polymers have been so high that the polymers cannot be melted and formed into useful articles in conventional process¬ ing equipment. Disclosure of Invention We have found that certain all-aromatic co¬ polyesters prepared from terephthalic acid, 2,6- naphthalene dicarboxylic acid, hydroquinone and resor¬ cinol have melting points that are low enough to permit' the copolyesters to be processed into useful articles, such as fibers and molded articles, in conventional equipment. The copolyesters of this invention are prepared from terephthalic acid, 2,6-naphthalenedicarboxylic acid, a diacyl ester of hydroquinone and a diacyl ester of resorcinol and can be defined as copolyesters having molecular weights suitable for forming fibers and containing the following divalent radicals: In our copolyestErs the range of terephthali acid is from 20 to 0 mole percent, based on the total moles of terephthalic acid and 2,6-naphthalenedicar- boxylie acid combined. Since the range of terephthali acid is based on the sum of the moles of terephthalic acid and 2,6-naphthalenedicarboxylic acid, at 20 mole percent terephthalic acid the copolyesters have 80 mol percent 2,6-naphthalenedicarboxylic acid and at 50 mol percent terephthalic acid the copolyesters have 50 mol percent 2,6-naphthalenedicarboxylic acid. In preferred copolyesters the range of tere¬ phthalic acid is from 30 to 45 mole percent, based on the total moles of terephthalic acid and 2,6-naphtha- lenedicarboxylic acid combined. Also In our copolyesters the amount of resor cinol is from 20 to 6 mole perent, based on the total moles of hydroquinone and resorcinol combined. Thus, at 25 mole percent resorcinol, the copolyesters have 75 mole percent hydroquinone, and at 65 mole percent resorcinol the copolyesters have 35 mole percent hydro quinone. In preferred copolyesters- the range of resor cinol is from 30 to 50 mole percent, based on the tota moles of resorcinol and hydroquinone. The precise manner In which the melting points of the copolyesters of the invention are unexpectedly lower than the melting points of similar copolyesters is illustrated in the Figure. In the Figure the amount of terephthalic acid, based on the total moles of terephthalic acid and 2,6- naphthalenedicarboxylic acid, has been plotted on the abscissa. The temperature in degrees Centigrade has been plotted on the ordinate. Melting points have been plotted for copolyesters of the invention, containing a quantity of terephthalic acid in the range of 20 to 50 mole percent, based on the total moles of tereph¬ thalic acid and 2,6-naphthalenedicarboxylic acid. Suitable curves have been drawn through the data points for copolyesters containing the same amount of resor¬ cinol. For example, the lowermost curve drawn through the closed circular data points represents the melting points of copolyesters containing 40 mole percent resor¬ cinol, based on the total moles of hydroquinone and resorcinol combined. The data for the copolyesters of the inven¬ tion were obtained by preparing each of the copolyesters using a process known in the art and then determining the melting points of each copolyester. The -copolyesters of the invention were pre¬ pared by an acidolysis procedure whereby terephthalic acid, 2,6-naphthalenedicarboxylic acid, a diacyl ester of hydroquinone and a diacyl ester of resorcinol were reacted under an increasing temperature ranging up to 3-*J0-3δ0°C. and a decreasing pressure to form a high molecular weight polymer. As a specific example, the following procedure was used to prepare a copolyester from 40 mole percent terephthalic acid and 60 mole per¬ cent 2,6-naphthalenedicarboxylic acid, based on the moles of terephthalic acid and 2,6-naphthalenedicarboxy- lic acid combined, and 60 mole percent hydroquinone and OMPI 40 mole percent resorcinol, based on the moles of hydro quinone and resorcinol combined. A mixture of 33•2 g. (0.20 mole) terephthalic acid, 64.8 g. (0.30 mole) 2,6-naphthalenedlcarboxylic acid, 38.8 g. (0.20 mole) resorcinol diacetate, and 66. g. (0.30 mole) hydroquinone dipropionate was placed in a 500-ml. flask equipped with a stirrer, short distilla tion column and an inlet for nitrogen. The flask was evacuated and purged three times with nitrogen and drie at 100-110°C. for 30 minutes at <0.3 mm. pressure befor being immersed in a bath at 275°C. After the mixture was stirred for 30 minutes at 280 C, the temperature was raised to 300°C. for 30 minutes and then to 325°C. for 30 minutes. Finally the temperature was raised to 355°C. for 25 minutes and a vacuum of 0.5 mm. was ap¬ plied. The polymerization was complete within 20 to 30 minutes. The tough, fibrous, opaque polymer obtaine had a softening point of 332°C. and a melting point of 34l°C. Fibers with tenacities >3 g./denier can be melt spun at 36θ°C. Heat-treated fibers had tenacities of 10 g./denier -and higher. The other copolyesters containing different amounts of 2,6-naphthalenedicarboxylic acid, tereph¬ thalic acid, hydroquinone and resorcinol were prepared by a similar procedure but using slightly different reaction temperatures because of differences in melt¬ ing points. Solid-phase polymerization also may be used to increase the molecular weight of the copolyesters of the Invention by heating polymer particles in an inert atmosphere or under reduced pressure at a tem¬ perature below that at which the particles will become tacky and tend to fuse together. Since this thermal treatment may give polymers with increased crystall- inity and melting points, compared to melt phase -BUR OM W1P polymerization, melt phase polymerization is generally preferred. Solid-phase polymerization is preferred, however, if the melting point is above 38O C. The melting points of the copolyesters of the invention were determined with a differential scan¬ ning calorimeter. The accompanying Figure shows that the melting points of the copolyesters of the invention containing 20 to 50 mole percent terephthalic acid and 20 to 65 mole percent resorcinol are unexpectedly lower than the melting points of copolyesters containing less than 20 or more than 50 mole percent terephthalic acid. For example, consider the copolyester which contains a con¬ stant value of 40 mole percent resorcinol and is repre- sented by the lower curve connecting the closed circular data points. When the amount of terephthalic acid is below 20 mole percent, the melting point is above 400 C. As the amount of terephthalic acid is increased, the melting point falls and reaches a minimum value of 330 C. at 30 mole percent terephthalic acid. As the amount of terephthalic acid is increased, the melting point increases and is 385 C. at 50 mole percent tere¬ phthalic acid. Although the details of the reduction in melting point have been discussed only for the copoly¬ esters containing 40 mole percent resorcinol, the same lowering of the melting point applies to the other co¬ polyesters of this invention. For example, the melting point of the copolyesters containing 20 and 60 mole per- cent resorcinol is also substantially lowered when from 20 to 50 mole percent terephthalic acid is used. Al¬ though melting point data is not plotted for copolyes¬ ters containing less than 20 mole percent terephthalic acid, it is clear from the shape of the curve melting points are above 400°C. A wide variety of diacyl esters of hydroqu one and resorcinol can be used to prepare the copoly esters of this invention. Examples of diesters Incl the diacetate, dipropionate, dibutyrate and dibenzoa The diacetate and dipropionate are preferred. The copolyesters of this invention can con tain minor amounts of other naphthalenedicarboxylic acid isomers in addition to the 2,6-isomer. Also, m amounts of dicarboxylic acids other than terephthali acid and diols other than hydroquinone can be used. The copolyesters of this invention can also contain nucleating agents, fillers, pigments, glass fibers, asbestos fibers, antioxidants, stabilizers, plastici -zers, lubricants, fire-retardants, and other additiv The inherent viscosity of the copolyesters of this invention cannot be determined because the c polyesters of this Invention are insoluble in typica solvents used for determining inherent viscosity. A though the inherent viscosity of the copolyesters of invention has not been measured, the molecular weigh of the copolyesters of the invention are high enough to be in the fiber-forming range. The minimum fiber forming molecular weight of the copolyesters is abou 5,000. In most cases copolyesters of the invention have molecular weights above 8,000 and can have mole cular weights as high as 20,000 and- in some instance the molecular weights can range up to 25,000 or even higher.

Claims: We Claim : 1. Copolyesters having a fiber-forming mole¬ cular weight and containing the following divalent radicals: the copolyesters being characterized by the amount of being from 20 to 50 mole percent, b ar *- nt of le percent, b and 2. The copolyester of Claim 1 wherein the range of the amount of is from 30 to 45 mole percent and the range of the amount of -8- is from 30 to 50 mole percent.

Inventors: JACKSON W, MORRIS J
Applicants: EASTMAN KODAK CO
Application year: 1979
Main classification: C08G63
IPC codes: C08G63, C08G69