EFFECT OF STRUCTURAL SYMMETRY ON GAS-TRANSPORT PROPERTIES OF POLYSULFONES

The effects of structural symmetry of phenylene linkages and methyl group placement on the properties of polysulfones have been investigated. Polysulfones with unsymmetric structures have lower gas permeability and higher selectivity coefficients than their symmetric counterparts. The polysulfones with m-phenylene linkages or dimethyl substitutions to the bisphenol unit have lower glass transition temperatures, lower fractional free volumes, and higher sub-T(g) relaxation temperatures. The chains of the unsymmetric polymers are generally more efficiently packed and appear to have greater mobility constraints, stemming from both intramolecular and intermolecular origins, than their symmetric counterparts, all of which influence properties and especially permeation behavior.