THERMAL-DEGRADATION STUDIES OF TEREPHTHALATE POLYESTERS .1. POLY(ALKYLENE TEREPHTHALATES)

Poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and poly(decamethylene terephthalate) (PDMT) have been prepared and their thermal stabilities have been studied by thermogravimetry (TG) and thermal volatilisation analysis (TVA). Both programmed and isothermal heating conditions have been employed, using a nitrogen atmosphere for TG and vacuum for TVA. In the latter case, the amounts of the main product fractions (residue, cold ring fraction, volatile products) have been determined quantitatively and the various materials present in the volatile and cold ring fractions have been separated and identified. There is a common degradation pattern for these polymers. All of the various products observed (except anhydride groups) have been explained by a homolytic route for the decomposition, which accounts for the continuous formation of CO and CO2, and differs from the non-homolytic mechanisms previously proposed in the case of PET. Anhydride structures, formed at the highest degradation temperatures, probably result from dehydration of pairs of carboxyl end groups formed at lower temperatures.