“…At elevated temperatures, well below its decomposition temperature, PVC loses HCl, and becomes discoloured, leading to changes in chemical and physical properties of the polymer. Thermal degradation of PVC is generally considered to be initiated at unstable structural irregularities (particularly tertiary and allylic chlorides) within PVC, and some authors [1][2][3][4][5] have claimed that these structural defects are responsible for the low thermal stability of the polymer. Although structural irregularities considerably increase the initial rate of PVC degradation, and indeed initial rates of degradation at low conversions (0.1 -0.3%) have been shown to correlate well with allylic and/or tertiary chloride content of PVC 6,7) , it has been argued that on account of the low concentrations in normal PVC of these structural irregularities, initiation of thermal degradation of PVC also takes place at regular monometric units [8][9][10][11][12] .…”