CRYSTALLIZATION ACCELERATOR FOR THERMOPLASTIC POLYESTER AND POLYESTER RESIN COMPOSITION CONTAINING SAME

PURPOSE:A crystallization accelerator which, when added to a thermoplastic polyester, causes less degradation of polyester, allows rapid crystallization and causes no softening of the resin, comprising a specified polyester oligomer. CONSTITUTION:A crystallization accelerator for thermoplastic polyesters, which comprises a polyester oligomer in which above 90mol% of the dicarboxylic acid residues are terephthalic acid residues and above 90mol% of the diol residues are 2-6C aliphatic diol residues (e.g., ethylene glycol residues), said oligomer having an intrinsic viscosity of below 0.4, and above 1mueq./g of groups of the formula, wherein Me is an alkali metal bound to molecular terminals. This crystallization accelerator, when added to a thermoplastic polyester, can suppress degradation of the polyester as low as possible and exhibit a large effect of promoting crystallization without detriment to the excellent properties inherent in the polyester.