Abstract: A process for preparing polyesters having superior thermal stability, transparency and chemical resistance, which comprises (1) a first step of esterifying (A) a difunctional carboxylic acid containing at least 60 mole% of an aromatic dicarboxylic acid, (B) 0 to 80 mole%, based on component (A), of an aliphatic diol and/or a dihydroxybenzene and (C) an aromatic monohydroxy compound in an amount of at least 210 mole% as a total of it and component (B) based on component (A), the esterification being performed until the degree of esterification reaches at least 80%, (2) subsequently, a second step of adding 0 to 80 mole%, based on component (A), of component (B) and a bisphenol (D) in an amount of 100 to 130 mole% as a total of it and component (B) based on component (A) to the reaction product obtained in the first step and reacting the mixture, the total amount of components (B) used in the first and second steps being 0 to 80 mole% based on component (C), and (3) performing at least the first of the above st

Abstract: High molecular weight, colorless polyesters suitable for shaping into filaments and films are obtained using novel catalysts selected from the group consisting of reaction products of specified antimony or zirconium (IV) compounds with (1) a carboxylate of calcium, manganese or zinc and (2) an acid anhydride, alcohol or glycol. The molar ratio of the antimony or zirconium compound to the aforementioned carboxylate is between 1:1 and 1:6. The catalysts are active in both transesterification and polycondensation. The rates of these reactions are more rapid than can be achieved using prior art catalysts.

Abstract: High molecular weight, colorless polyesters suitable for shaping into filaments and films are obtained using novel catalysts selected from the group consisting of reaction products of specified antimony or zirconium (IV) compounds with 1) a carboxylate of calcium, manganese or zinc and 2) an acid anhydride, alcohol or glycol. The molar ratio of the antimony or zirconium compound to the aforementioned carboxylate is between 1:1 and 1:6. The catalysts are active in both transesterification and polycondensation. The rates of these reactions are more rapid than can be achieved using prior art catalysts.

Abstract: This invention relates to crystallizable polyester compositions having improved molding characteristics. Crystallization rates and properties are improved by the addition of a polymer derived from meta or para diisopropenyl benzene and such polymers terminated by .alpha.-methyl styrene.