Effects of sample history, time, and temperature on the sorption of monomer vapor by PVC

The sorption of vinyl chloride monomer (VCM) vapor by poly(vinyl chloride) (PVC) resin powders has been studied as a function of time, VCM pressure, temperature, and previous PVC history. In fine powders, sorption occurs in two separable stages, a rapid Fickean diffusion and a slow relaxation-controlled process. Hysteresis in interval sorption-desorption experiments and variable resorption behavior can be related to the relaxation-controlled process. The amount of VCM sorbed shows a pronounced variation with postpolymerization thermal history of the PVC sample; this effect seems to result from the freezing-in of differing “hole volumes” under varied conditions of glassification. The heat of VCM sorption by glassy PVC, −4.3 kcal/mole, is nearly equal to the heat of condensation of VCM. The complex dependence of sorption behavior upon experimental variables can reasonably be interpreted as reflecting changes in hole volume with postpolymerization history.