Thermal degradation studies of alternating copolymers VII. Degradation of the alternating copolymer of allyl acetate and maleic anhydride: structural changes and degradation mechanism

摘要

The alternating copolymer of allyl acetate (AllA) and maleic anhydride (MAn) has been prepared by the free radical route at 60℃. The previous investigations of the nature of the evolved products have been supplemented by studies of structural changes in the degrading copolymer by FTIR spectroscopy. Changes have been investigated both under programmed heating at 10℃/min to near 500℃ and under milder conditions using isothermal heating for up to 6 h at 200℃. Anhydride absorption begins to decrease from 200℃, initially with loss only of carbon dioxide and the development of cyclic ketone structures in the chain. Subsequently ester absorption can be seen also to decrease as the temperature is increased, and α,β -unsaturated ketone structures are formed. The isothermal studies confirm that the acetate groups remain stable in this copolymer under mild conditions while the anhydride structures slowly degrade, in contrast to the alternating copolymers of maleic anhydride with vinyl acetate or isopropenyl acetate, in which the reverse is true. A degradation mechanism is proposed.