PREPARATION OF COPOLYESTER

PURPOSE:To obtain the subject copolymer having three specified structural units at a specified ratio, being moldable by means of a usual molding machine and having excellent optical anisotropy, high-temp. impact resistance and rigidity, by acylating hydroxyl groups of a specified polyester raw material with acetic anhydride. CONSTITUTION:A copolyester consisting of structural units of formulas I-III wherein formulas I+II are 77-95mol%, formula III is 23-5mol% of the whole and the molar ratio of formula I to formula II is 75/25-95/5 is obtd. by acylating hydroxyl groups of a polyester raw material consisting of p- hydroxybenzoic acid (A), an arom. dihydroxyl compd. (B) such as 4,4'- dihydroxybiphenyl and hydroquinone, an arom. dicarboxylic acid (C) such as terephthalic acid and 4,4'-dicarboxybiphenyl and a polyester (D) prepd. by con densing the component C with an alkylene glycol having a logarithmic viscosity of 0.3dl/g or smaller and carrying out deacetylation-polymn. thereof. In the formulas, R1 is formula IV, V, VI or VII etc.; R2 and R3 are each formula IV, V, VI or VIII; X is H or Cl; R4 is formula IX and n is 2-6.