Polybutylene terephthalate (PBT) is a thermoplastic polymer that, owing to its valuable physicochemical properties, is widely used in the motor industry, in electronics, and in electrical engineering (refs. 1 and 2). However, in a number of cases, because of the relatively low thermal stability of PBT, the combination of physicochemical properties built into its structure is partially lost during processing from the melt (ref. 3). In view of this, investigations were carried out to improve the resistance of PBT to heat and oxygen and to lengthen its service life.