GAS-TRANSPORT PROPERTIES OF POLYPHENYLENE ETHERS

Gas transport properties of the polyphenylene ethers poly (2,6-dimethyl-1,4-phenylene oxide), PDMPO, and poly(2,6-diphenyl-1,4-phenylene oxide), PDPPO, and the thioether poly(1,4-phenylene sulfide), PPS, have been measured as a function of pressure and temperature. The PPS material and free volume correlations were used to estimate the behavior of the unavailable poly(1,4-phenylene oxide), PPO. The results show that symmetrical substitution of phenyl groups on the backbone of polyphenylene ether, PDPPO, increases the gas transport properties by one order of magnitude relative to the unsubstituted material, PPO. Symmetrical methyl substitution, PDMPO, however, increase the permeability, apparent diffusion and sorption coefficients even further. The gas transport coefficients correlate with the fractional free volume of the polymers. PDMPO has the largest fractional free volume and gas transport coefficients followed by PDPPO and then PPS. The results show that substitution of phenyl groups, which leads to polymers that have better thermal and oxidative stability than methyl substituted ones, can be a useful means for increasing free volume and gas permeability coefficients. While methyl groups appear to be more effective for the latter, the enhanced chemical stability of phenyl rings may be useful when gas separation membranes are to be used in harsh environments. (C) 1993 John Wiley & Sons, Inc.