Membranes of triphenylsilyl substituted polyphenylene oxide in the permeation of propylene and propane gases

Poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) was chemically modified by the attachment of a bulky triphenylsilyl (TPS) group substituent (～30 mol %) to study its impact on hydrocarbon gas permeation. A membrane of the modified PPO (TPS–PPO) was tested for the permeation of pure propylene and propane gas and that of their 55:45 binary mixture at 30 ± 2°C. Gravimetric single‐gas equilibrium sorption studies were carried out to determine the gas solubility coefficients and diffusion coefficients to assess their role in the gas permeation mechanism of the membranes. Characterization studies were done to determine the interrelationship between the transport properties and the polymer structure. The studies included density, fractional free volume, Fourier transform infrared spectroscopy, ¹H‐NMR, differential scanning calorimetry, wide‐angle X‐ray diffraction, tensile testing, and scanning electron microscopy. The TPS–PPO membrane was found to be 3 times more permeable to propylene and 3.8 times more permeable to propane with a small decrease in the propylene/propane ideal permselectivity (3.37) when compared to that of unmodified PPO (4.25). TPS–PPO could be a potential membrane material for the efficient recovery of propylene and propane from mixtures with permanent gases such as those found in refinery off‐gas. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013