PURPOSE: To obtain a copolyester having excellent thermal stability through such processes that a specific polyester is brought into contact with a specific compound and depolmerized, and the resultant depolymerized product is subjects to polycondensation in the presence of a specific carboxylic acid.
CONSTITUTION: A polyester made up of a structural unit of formula I (R1 is an aromatic or an aliphatic group; R2 is an aliphatic or an alicyclic group) is brought into contact with an acylated hydroxycarboxylic acid of formula II (Ar is an aromatic group; Ac is an acyl group) and depolymerized to give a depolymerized product, which is then subjected to polycondensation at reduced pressures. The whole process including the depolymerization and polycondesation is performed in the presence of 0.1-5mol.%, based on the compound of formula II, of a monofunctional aromatic carboxylic acid, thus obtaining the objective copolyester made up of the structural unit of formula I and the residue unit of the compound of formula II at the molar ratio A/B of (5:95) to (60:40).
SHIBA YOSHITO
YOSHIDA TOMOMI
