Degradation studies of some polyesters and polycarbonates: Part 4—Poly(ethylene oxalate)

Abstract

Techniques used in previous studies of the thermal degradation of polylactide (Parts 1 and 2) and polyglycollide (Part 3) have been applied to poly(ethylene oxalate). The monomer has been found to be stable under vacuum but to undergo some spontaneous polymerisation on storage in air at atmospheric pressure. Polymerisations have been carried out under nitrogen at 150–160°C, with and without catalyst. The polymer is less stable than polylactide and polyglycollide, showing a threshold temperature for decomposition under programmed heating (10°/min) at about 200°C and a rate maximum in the region of 320°C. The products of degradation are monomer, oligomer, carbon dioxide, carbon monoxide, ethylene, acetaldehyde and several other minor products. In isothermal degradation at 260°C under vacuum, the products included 49% by weight monomer and 30% oligomer; the major components making up the remaining 21% of the original sample weight comprised carbon dioxide, carbon monoxide and ethylene. There is negligible involatile residue of degradation. A mechanism is presented in which homolysis at the oxalate linkage is proposed as the initial process, all the observed products being explicable by subsequent scissions of the initially formed macroradical.