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Pyrolysis of Poly(vinyl Chloride) 3 4 E. P. CHANG and R. SALOVEY, Hooker Research. Center, Hooker Chemical Corporation, Niagara Falls, New York 14303 Synopsis A pyrolysis-gas chromatography-moss spectrometric technique has been developed 1 to study the thermal degradation of poly(vinyl chlorides) polymerized at different temperatures. Hydrogen chloride and benzene evolution during successive stages of pyrolysis have been quantitatively determined and correlated to the tactieity and ~jk molecular weight of the polymer. It was found that lowering the temperature of polymerization and molecular weight depresses benzene evolution and increases char weight but does not affect the HC1 yield. It is suggested that the syndiotactie Irons microstructure favored at low temperature of polymerization yields polyenes which cannot cyclize to form benzene. As the molecular weight decreases, the increase in number of vinyl chain ends facilitates pyrolytic crosslinking and char formation. INTRODUCTION It is well known that thermal degradation of poly(vinyl chloride) (PVC) evolves HC1, and the dehydrochlorination proceeds along the polymer chain resulting in the formation of a conjugated polyene which is'responsible for the dark color of the degraded polymer.1 The initial reaction is believed to be the elimination of a chlorine atom adjacent to a carbon-carbon double bond or at a tertiary' C--Cl bond which is weaker than a secondary C--Cl site.1 Stromberg,* in studies of the thermal degradation of PVC at 400C for 30 min under vacuum, identified approximately' 25 hydrocarbon products after stripping the resin of HC1 at temperatures up to 350C for 30 min. Otani and Ishikawa4 pyrolyzed PVC at 425C in a nitrogen atmosphere and studied the resulting degradation products by infrared and ultraviolet spectroscopy'. They found that PVC of higher syndiotacticitv produced shorter-chain alkyl-substituted aromatics. Thinius ct a!.1 showed by gas chromatography the presence of saturated and unsaturated hydrocarbons up to Cs, benzene, toluene, and other aromatic materials during the de composition of PVC in air. In addition, they reported traces of chlori nated hydrocarbons, formaldehyde, and certain other oxygenated species. J Noffz et al.,` using pyrolysis chromatography with capillary columns, demonstrated that the hydrocarbon degradation products consisted mainly of aromatic compounds, while a volatile aliphatic hydrocarbon fraction was too complex to be identified. Wolley detected by gas chromatography of the thermal decomposition product of VVC approximately 7f> organic 2927 1974 by Jntin \ViI*y Sc Sons, Inc. TENO 585 ;