Thermal Degradation of Polyesters. 1. Aliphatic Polymers

摘要

A study was made of the pyrolysis of eight aliphatic polyesters prepared from various diacids and diols. The polymers start to degrade about 275C by random scission of the ester linkage and are comparable to poly(ethylene terephthalate) with respect to thermal stability. Providing a beta-hydrogen atom is available in the diol portion of the ester, which was the case for the polymers studied, the classical cyclic mechanism observed for the decomposition of simple esters is applicable. Differences in degradation behavior are best explained in terms of secondary reactions which are dependent upon the nature of the end groups formed by scission and on the chain length of the acid and diol used to prepare the polymer. Thus, olefinic end groups break down to aldehydes, dienes, cyclic ethers and enols while acid end groups give carbon dioxide, cyclic detones (C5-C7 diacids) and cyclic anhydrides (C4, C5 diacids). Water is produced by anhydride formation and dehydration of hydroxyl end groups. The overall kinetics were consistent with a random mechanism but deviations from the simple random picture were concluded for some polymers and probably resulted from cross linking. Kinetic parameters were evaluated from programmed TGA data. (Author)