Spectroscopic studies of carbons. XIV. The vacuum pyrolysis of non-oxygen containing materials : PVF

Abstract

Although the degradation of polyvinyl fluoride (PVF) has been studied, emphasis has been placed on weight loss analyses and the study of the gases evolved during the degradation process. Little is currently known about the nature of the pyrolytic residue or of the chars which are formed during thermal degradation at higher temperatures. Fourier transform beam deflection spectroscopy was used in this study to examine chars produced by heating pure PVF in vacuum at temperatures ranging from 110°C to 685°C. The infrared spectra of the chars provide direct information about the degradation and subsequent carbonization of PVF. PVF exhibits a higher thermal stability than the polyvinyl halides which we have previously examined and consequently the first spectral evidence of degradation is not observed until 300°C. This higher temperature, which accompanies the initial loss of fluorine, suppresses the formation of long polyenic sequences and results in an overall degradation mechanism which consists of overlapping reactions involving polyene formation, chain scission, cross-linking and intramolecular cyclization. At temperatures above 500°C the aliphatic and aromatic structures formed during the first stages of the degradation process are replaced by a growing aromatic network. The spectral evidence for the occurrence of many of these reactions is presented in detail.