Free volume structure and transport properties of glassy polymers—materials for separating membranes

Abstract

The structural organization and transport properties for various glassy polymers being utilized or having potential to be applied as the materials of separating membranes are discussed. Among them are poly(vinyltrimethylsilane) (PVTMS), poly(trimethylsilyl-1-propyne) (PTMSP), and poly(phenylene oxide) (PPO). In addition, the data for other glassy and rubbery polymers are included into consideration for the comparison. Free volume of polymers was estimated by sorption of low-molecular-weight probe molecules at various pressures and temperatures, by positron annihilation method, by density technique including calculations by means of group contributions. Transport characteristics of polymers investigated were studied by sorption-desorption and permeation techniques. It was shown that highly permeable glassy polymers may posses free volume fraction on the level of that for highly permeable rubbers. This free volume has non-equilibrium nature and exist in the glassy polymer as a interconnected microporous network. Glassy polymers have heterogeneous structure consisting of the regions with ordered and disordered structures. The regularities of gas sorption in and transport through the glassy polymers and rubbery ones are different. The following sequence of changing in gas sorption and diffusion mechanism can be proposed: liquids, rubbery polymers, glassy polymers, highly permeable glassy polymers, microporous sorbents. © 1991 The Society of Polymer Science, Japan. All Rights Reserved.