Thermal degradation studies of alternating copolymers. III. The copolymer of maleic anhydride with trans-stilbene

Abstract

A comprehensive investigation of the copolymer of maleic anhydride and trans-stilbene (prepared using a free radical initiator) by IR spectroscopy, 1H-NMR spectroscopy, microanalysis and thermal analysis has justified its alternating structure. In addition, no evidence for crosslinking has been found. The thermal degradation of the copolymer has been studied by thermogravimetry under nitrogen and by thermal volatilisation analysis (TVA) under continuous evacuation, in both cases using programmed heating at 10 °C/min. The main product fractions of non-condensable gases, condensable gases and volatile liquids, tars and waxes and residue were isolated by TVA. The volatile decomposition products were further separated and characterised using subambient TVA, IR spectroscopy, mass spectrometry and GC-MS. Structural changes in the partly degraded copolymer have been examined by IR spectroscopy. A single stage of breakdown with a rate maximum in the region of 400 °C was observed by TVA. The major products consisted of a mixture of compounds which were non-volatile at ambient temperature and collected in the cold ring (tar/wax) fraction. This mixture was analysed in greater detail for isothermal degradation at 300 °C and was found to consist of stilbene, unsaturated ketones, aromatic lactones and unsaturated hydrocarbons, with or without phenyl substituents. Volatile products consisted almost entirely of carbon dioxide and carbon monoxide. On the basis of these results, a mechanism of degradation has been proposed. It is suggested that scission occurs by more than one route in the anhydride rings, accompanied by backbone scission.