Sorbate-induced structural rearrangements and permeation of gases in the polyphenylene oxide copolymer

Rearrangements of the porous structure of the glassy polyphenylene oxide copolymer occurring in the course of its swelling in the atm. of several gases and the subsequent relaxations were investigated using the low temp. nitrogen adsorption technique. The values of porosity (.vepsiln.) and BET surface area (SBET) were used to quantify the copolymer's free vol. accessible to N2 mols. at 77 K. The magnitude and the rate of changes of the copolymer's free vol. invoked by its conditioning in vacuum, N2, O2, CH4, CO2 and C3H6, were analyzed in terms of .vepsiln. and SBET. These characteristics of the polymer structure were found to depend upon the sorbate nature, its pressure, exposure time and temp. Swelling of the copolymer that occurs in certain atmospheres results in the expansion of the free vol., which is reflected in the increased values of .vepsiln. and SBET. In accordance with the magnitude of the copolymer swelling under exptl. conditions employed in this study, the gases can be qual. ranked as follows: C3H6 > CO2 > CH4 > O2 ~ N2. The swollen polymer, being placed in the environment of a lower swelling ability, experiences structural relaxations. The relaxations result in a decrease of the free vol., which is reflected by a decrease in the values of .vepsiln. and SBET. Gas permeability of glassy polymer membranes is directly related to the conditioning history of a polymer: the state of the glassy polymer characterized by the increased values of porosity and BET surface area corresponds to the more permeable state of a membrane. [on SciFinder (R)]