Effects of oxygen on thermal dehydrochlorination of poly(vinylidene chloride)

The early stages of thermal degradation below 1% dehydrochlorination poly(vinylidene chloride) (PVDC), can be divided into an induction period, period with conversion below 0.1% dehydrochlorination, and that with conversion ranging from 0.1 to 1%. The time of induction period increases with oxygen concentration due to retardation effect. The second and third stages of degradation follow the apparent zero-order reaction and rates of dehydrochlorination of both stages increase linearly with oxygen concentration. The melting points of samples with different degrees of degradation show a decreasing trend with degrading time regardless of annealing effect. By combination with our differential scanning calorimetry (DSC) thermograms and wide-angle X-ray diffraction (WAXD) patterns, in the presence of pure oxygen which first reacts with the PVDC dangling chains outside the crystalline, and cuts through the degraded crystalline along the backbones resulting in many pieces of small crystallite. A polarity change of PVDC characterized by solid-state nuclear magnetic resonance (NMR) due to degradation can be observed.