This paper presents a study of the reactions involved in stabilization of polyacrylonitrile (PAN) through the effect of various experimental variables on the differential scanning calorimetry (DSC) exotherm and thermogravimetric measurements coupled with Fourier transform infrared (FTIR) spectroscopy, i.e., DSC-FTIR and TG-FTIR. The experimental variables used were the environment of heat treatment (viz. oxidative and inert) and incorporation of an acidic comonomer (viz. itaconic acid). The essential findings include the broadening of the exotherm in an air atmosphere over that in a nitrogen (i.e., inert) atmosphere. This broadening of the exotherm was further enhanced in the presence of the acidic comonomer. Furthermore, the exotherm revealed a doublet character with greater separation of the peaks in case of the copolymer than the homopolymer. Possible explanations of these observations are discussed.