Dielectric study of the transition temperature regions for poly (vinyl chloride) and some chlorinated poly(vinyl chlorides)

Abstract

AbstractAudio frequency dielectric constant data versus temperature data for poly(vinyl chloride) exhibit a high temperature (glass) transition which becomes steeper and reaches higher values as the frequency is reduced. The same trend is demonstrated for a series of chlorinated poly(vinyl chlorides) although the transition decreases in magnitude and moves to higher temperatures systematically with increasing chlorine content. Corresponding loss data are presented. Dielectric constant values for poly(vinyl chloride), determined in the high temperature transition region from reversible (d.c.) polarization experiments, show that the trend to steeper and larger transitions continues as polarization lime increases. For 10,000 sec. polarization the curve exhibits a sharp peak with lambda point character and twice the highest a.c. value is reached. This dielectric constant peak is interpreted as a cooperative interaction in noncrystalline regions of long‐rod dipoles with moments perpendicular to the chain axes. This model is related to Natta's crystal structure for syndiotactic PVC where the assembly of planar molecules form an antipolar array. For PVC all the chlorines are on the same side of the axis but for chlorinated PVC, dipolar balancing due to 1,2‐dichloro groupings is responsible for the reduced transition magnitude. The high temperature process involves equilibrium of macroscopic volumes, whereas the low temperature transition, which is little affected by chlorination, involves local equilibrium only.