Process for preparing polyester elastomers

Claim 1

In a process for preparing a block copolyester elastomer having a softening point of at least 120° C by reacting an aromatic polyester (I) having a reduced viscosity of at least 0.4 and derived from an aromatic dicarboxylic acid or its ester-forming derivative as a main acid component with an aliphatic polyester (II) having a reduced viscosity of at least 0.4 and derived from an aliphatic dicarboxylic acid or an aliphatic hydroxycarboxylic acid or an ester-forming derivative of each of these acids in the molten state; the improvement wherein A. the aromatic polyester (I) is derived from a dicarboxylic acid component more than 70 mole % of which consists of terephthalic acid and diol component more than 70 mole % of which consists of tetramethylene glycol or trimethylene glycol, B. the weight ratio of the aromatic polyester (I) to the aliphatic polyester (II) is 0.25 to 9, and C. the reaction between the polyester (I) and the polyester (II) is carried out until a polymer is obtained which has an elasticity recovery of at least 50% after it is stretched 20% and then relaxed for 5 minutes, the reaction of the polyester (I) with the polyester (II) being carried out in the presence of a titanium-type catalyst, and after the reaction has proceeded to the stage of (C), at least one compound selected from the group consisting of phosphorus compounds of the formula ##STR5## wherein R 1 and R 2 are identical to, or different from, each other, and represent a hydrogen atom, an alkyl, cycloalkyl, aralkyl or aryl group each containing not more than 20 carbon atoms or OR 3 in which R 3 represents a metal, ammonium or the same group or atom as R 1 independently from R 1 , diaryl dicarboxylates of the formula AOOC -- X.sub.n -- COOB wherein n is 0 or 1, X is a divalent organic group, and A and B are identical to, or different from, each other and represent a monovalent aryl group containing 6 to 20 carbon atoms and being free from an ester-forming functional group, carbonic acid esters of the formula ##STR6## wherein R 4 and R 5 are identical to, or different from, each other, and represent an aryl group containing no ester-forming functional group, and ortho-carbonate compounds of the formula ##STR7## wherein R 6 , R 7 , R 8 and R 9 are identical to, or different from, each other, and represent a monovalent aryl group containing no ester-forming functional group, being added in an amount which stops or inhibits the above reaction.