Thermal behavior of polymethacrylonitrile

Abstract

The intramolecular cyclization by heating and the thermal degradation of polymethacrylonitrile samples prepared with various initiators, AIBN (A), BPO (B), BuLi (C), Et2Mg (D), and methacrylonitrile–methacrylic acid copolymer (E), were investigated by DTA, TGA, and infrared spectroscopy. The rate of formation of CN linkages determined by IR was in the order of E > C > D > B > A. An endothermic peak of DTA thermogram due to thermal degradation was observed at approximately 345°C for the ionically initiated samples, whereas two endothermic peaks were observed at approximately 315°C and 365°C for the radically initiated ones. In the TGA thermograms, although the ionically initiated samples decomposed continuously in a single stage, the radically initiated ones showed weight loss in two steps, with an inflection point at about 330°C. The first stage of thermal degradation of radically initiated samples was concluded to be initiated at the terminal double bonds formed as a result of termination by disproportionation, and the second one at higher temperatures is initiated at random in the polymer. The ionically initiated samples without terminal double bond decompose exclusively by random scission.