Abstract
Glassy polymers of the polyphenylene oxide series (PPOs) were investigated using the low-temperature nitrogen adsorption and 129Xe NMR spectroscopy techniques. The experimental data are indicative of a developed system of interconnected microcavities existing in the polymers. The intrinsic microporosity of PPOs is most probably formed by a continuous three-dimensional network of molecular-sized interstices between the rigid-chain macromolecules. These supposedly constitute the free volume of the polymers. The micropores are likely to be of the ‘throat and cavity’ type, where a cavity may possess 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 molecules occurs through these micropores. Variations in gas permeability and sorption characteristics, which are dependent on the previous history of the polymer, were investigated and interrelations between these features analyzed. Crystallinity vs. gas permeability relationships for PPO membranes were studied. It is concluded that crystalline and amorphous phases of polyphenylene oxides have similar gas permeabilities for the experimental conditions employed. Analysis of the experimental data shows that it is justified to look upon polyphenylene oxides as polymeric analogues of solid microporous adsorbents.
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