Effect of carboxylic end groups on thermooxidative stability of PET and PBT

A series of poly(ethylene terephthalate) and of poly(butylene terephthalate ) samples containing different amounts of carboxyl end groups were prepared by chain-extension reaction with diepoxides. The effect of the carboxyl co ntent on thermooxidative degradation was studied, using as criteria the ind uction period of oxidation and the stabilisation coefficient, both obtained by differential scanning calorimetry during isothermal or dynamic heating of the samples under air and nitrogen atmosphere. It was found that as the carboxyl content decreases the thermooxidative stability increases. However , in some more chain extended (crosslinked) samples the thermooxidative sta bility degreased. This abnormal behaviour was attributed to the lower degre e of crystallinity of these samples. (C) 1999 Elsevier Science Ltd. All rig hts reserved.