GAS-TRANSPORT IN POLYURETHANE POLYSTYRENE INTERPENETRATING POLYMER NETWORK MEMBRANES .2. EFFECT OF CROSS-LINKED STATE AND ANNEALING

Abstract

A series of polyurethane (PU)-polystyrene (PS) interpenetrating polymer network (IPN), semi-IPN (only PU component crosslinked) and linear blend membranes were prepared with varying synthesis temperature and composition. PU was first thermally polymerized, and then PS was polymerized by photolytic methods at two different temperatures, 0-degrees-C and 40-degrees-C. The permeability coefficient decreased and the separation factor increased when preparation took place at the lower temperature due to the increase in homogeneity of PU and PS as shown in the previous papers. The minimum permeability coefficient and the maximum separation factor were observed at a composition with ca. 25 wt.% PU. The permeability coefficient increased in the following sequence; IPN, semi-IPN and linear blends. Thermal annealing was adopted to study the effect of homogeneity of the two polymer components in the membrane on the gas permeation characteristics. Annealing was found to increase the permeability coefficients, while it caused a decrease in selectivity and the extent of synergistic behavior. The annealing effect on the permeation characteristics depended on the nature of crosslinking of the membrane (IPN < semi-IPN < linear blends). It was shown that a change in homogeneity, modulated by change of composition, state of crosslinking, synthesis temperature and annealing temperature etc., could play an important role in controlling the gas transport characteristics through the multicomponent polymeric membranes. The observed permeability characteristics were also substantiated by considering the densities and the degree of relative intermixing (by means of T(g) variations).