Intrinsic microporosity and gas transport in polyphenylene oxide polymers

Glassy polymers of the polyphenylene oxide series (PPOs) were investigated using the low-temperature nitrogen adsorption and Xe-129 NMR spectroscopy t echniques. The experimental data are indicative of a developed system of in terconnected microcavities existing in the polymers. The intrinsic micropor osity of PPOs is most probably formed by a continuous three-dimensional net work of molecular-sized interstices between the rigid-chain macromolecules. These supposedly constitute the fi ee volume of the polymers. The micropor es are likely to be of the 'throat and cavity' type, where a cavity may pos sess several throats. Effective diameters of the throats were estimated to be approximately 0.4 nm at 77 K. It is believed that transport of gas molec ules occurs through these micropores. Variations in gas permeability and so rption characteristics, which are dependent on the previous history of the polymer, were investigated and interrelations between these features analyz ed. Crystallinity vs. gas permeability relationships for PPO membranes were studied. It is concluded that crystalline and amorphous phases of polyphen ylene oxides have similar gas permeabilities for the experimental condition s employed. Analysis of the experimental data shows that it is justified to look upon polyphenylene oxides as polymeric analogues of solid microporous adsorbents. (C) 1999 Elsevier Science B.V. All rights reserved.