Branched thermoplastic copolyesters

Claim 1

In a process for preparing a segmented thermoplastic copolyester, said copolyester consisting essentially of a multiplicity of recurring long chain ester units and short chain ester units joined head-to-tail through ester linkages, said long chain ester units being represented by the formula ##EQU4## and said short chain units being represented by the formula ##EQU5## which comprises reacting a dicarboxylic acid having a weight less than about 300; said acid being represented by the formula ##EQU6## wherein R is a divalent radical and R' is independently selected from the group consisting of hydrogen and C 1 -C 10 alkyl; a poly(alkylene oxide) glycol having a molecular weight of about 400-4,000 and a carbon to oxygen ratio of about 2.0-4.3 said glycol being represented by the formula HO--G--OH wherein G is a divalent radical, and a diol having a molecular weight less than about 250 and represented by the formula HO--D--OH wherein D is a divalent radical, the improvement which comprises conducting the reaction in the presence of about 0.3 to 1.2 equivalents per 100 moles of said dicarboxylic acid of a branching agent, said branching agent being represented by the formula (HO) a X (COOH) b wherein X is a polyfunctional radical, a = 0-6, b = 0-4 and a + b = 3-6, said branching agent having a molecular weight of about 92 to 5,000.