DIELECTRIC-RELAXATION PROPERTIES OF LINEAR POLYESTERS DERIVED FROM BETA-PROPIOLACTONE

Dielectric relaxation measurements are reported over a frequency range of 0.01-50 kHz and from 100-490 K for a series of poly(alpha-dialkyl-beta-propiolactones): poly(alpha-dimethyl-beta-propiolactone) (PPL), poly(alpha-methyl-alpha-ethyl-beta-propiolactone) (PMEPL) and poly(alpha-methyl-alpha-n-propyl-beta-propiolactone) (PMPPL). First of all, the three polyesters investigated show a high temperature beta-relaxation peak which is due to their glass transitions. Secondly, PPL and PMEPL exhibit a gamma relaxation peak, at 275 and 210 K, respectively, which is related to the crystalline fraction of the polyester since its intensity increases with the degree of crystallinity. PMPPL does not show such a relaxation due to its low degree of crystallinity. Thirdly, a weak delta relaxation peak is observed at low temperatures (approximately 130 K) for PMPPL and PMEPL. This peak is absent in PPL. This observation suggests that the delta peak is due to ethyl and propyl group rotations around the main chain of the linear polyester in its amorphous fraction; PPL does not show this relaxation since it has only methyl substituents and a high degree of crystallinity. Finally, the beta, gamma, and delta relaxation data of these three polyesters were analysed using a method based on the frequency-temperature superposition principle and using the Cole-Cole representations.