Influence of polymerization conditions on the glass transition temperatures of pvc powders

Abstract

Abstract A drop in glass transition temperatures, of as-polymerized poly (vinyl chloride) powders made at low temperatures, between the first and subsequent DSC runs has been reported in the literature. This was interpreted earlier as a consequence of decrease in crystallinity. It has recently been shown that the crystallinity does not decrease in such DSC runs but in fact it increases or remains constant. A simplified analysis, therefore, has been done to explain the observed drop in glass transition temperatures of the as-polymerized poly(vinyl chloride) powders made at low temperatures. It is proposed that the initial high glass transition temperature is due to internal stresses introduced in the particle during the polymerization stage. Based on non-Gaussian chain statistics, an expression has been developed which can be used to evaluate the drop in Tg for a critical extension ratio, and predicts this drop to be inversely proportional to conversion. The experimental conversion−ΔTg data reported in thi...