Sorption kinetics and equilibria in annealed glassy polyblends

Abstract

AbstractThe sorption kinetics and equilibria of n‐hexane in glassy polyblends of polystyrene and poly(2,6 dimethyl‐1,4 phenylene oxide) were studied as a function of annealing conditions. Cast film samples were annealed 20°C above their respective glass transition temperatures for two hours and twenty‐four hours. The rate of relaxation‐controlled (Case II) sorption of n‐hexane in these films was reduced markedly consequent to annealing. The effect of annealing on the sorption kinetics and the independently determined film densities was more pronounced for the poly(phenylene oxide)‐rich samples. Although sorption rates were reduced by as much as a factor of 100, the sorption equilibrium was insignificantly affected by annealing. Super Case II transport was observed for the slow absorbing annealed samples whereas the more rapid sorption in the unannealed samples followed ideal Case II kinetics. The more pronounced effects of annealing for the poly(phenylene oxide)‐rich samples on sorption rates and film densities were explained by considering the increasing difference between the film Tg and the drying temperature used in the original film preparation for the poly(phenylene oxide)‐rich samples. These results suggest that glassy polymers, cast and dried well below their glass transition temperatures, will be subject to large long‐term reductions in absorption rates and specific volume. Moreover, residual, excess free volume significantly affects relaxation‐controlled absorption of vapors in partially annealed glassy polymers.