Studies on the Degradation of Poly (Vinyl Chloride)

Abstract

The industrial significance of studies on the degradation of poly(vinyl chloride), or PVC, was discussed and the literature relating to the causes and mechanism of the degradation reaction reviewed. Apparatus for measuring the rate of degradation of PVC in bulk form and in solution was described and details given of the experimental technique. Different kinetics were observed depending on whether the polymer was studied in bulk or in solution and this was explained in terms of the catalytic effect of hydrogen chloride. Samples of PVC prepared to different conversion and at different temperatures were found to degrade at a rate which was directly related to their temperature of polymerisation but independent of the extent of conversion to polymer. Infra-red measurements showed that the degree of branching was also independent of the extent of conversion. Polymer fractions with different molecular weights obtained by precipitation from solution degraded at a uniform rate. It was concluded that branch points are of major importance in initiating the dehydrochlorination of PVC. A study was made of the kinetics of degradation in solvents and solvent mixtures and the effect of inhibitors for free-radical reactions on the degradation rate. The results did not clarify the nature of the mechanism of the reaction in the absence of oxygen. The thermo-oxidative degradation of PVC in solution was also studied and a reaction mechanism involving direct attack of oxygen on the macromolecule suggested.