Preparation of high molecular polyesters of 1,4-butanediol

Claim 1

A process for the condensation of diols and dicarboxylic acid dialkyl esters wherein 1,4-butanediol or its mixture with at most 10 mol percent of another diol is condensed with a member selected from the group consisting of dialkyl esters of terephthalic acid, dialkyl esters of isophthalic acid and mixtures thereof or said selected member with at most 10 mol percent of at least one other dicarboxylic acid dialkyl ester, and wherein a. 1 mol of the dicarboxylic acid dialkyl ester is transesterified with 1.05 to 1.9 mols of the diol in the presence of 0.01 to 0.4 percent by weight of titanic acid tetraalkyl ester based on the dicarboxylic acid dialkyl ester, at a pressure of 2-10 bars and a temperature of 180° to 230°C., b. the trans-esterification product is polycondensed in the melt at 230°-300°C. under reduced pressure of 0.1 to 5 mm Hg and c. the polyester thus obtained is further condensed at a temperature of 5° to 50°C. below its melting point, under reduced pressure or under an inert gas atmosphere, until its intrinsic viscosity is from 0.6 to 1.9 dl/g.