The thermal and thermooxidative stability of polybutylene terephthalate (PBTP), synthesized in the presence of the optimal stabilizing system, has been investigated. The basic products of PBTP degradation and the regularities of their formation in the temperature regime close to the temperature regimes of its processing were determined. The investigations conducted allowed recommendations to be made on the temperature regimes of PBTP processing because even a small excess of the chosen temperature (265degreesC) leads to polymer chain fragmentation. (C) 2004 Wiley Periodicals, Inc.