Structural effects on free volume distribution in glassy polysulfones: Molecular modelling of gas permeability

Molecular mechanics and molecular dynamics have been used to build amorphous cells of 13 different aromatic polysulfones. The amorphous-state disorder was analysed in terms of pair correlation functions. Relaxed and equilibrated cells were generated and the cohesive energy density and the solubility parameters calculated. Variations in the solubility parameters were related to polymer structure, and to experimental glass transition temperature, T-g, values for the polymers. The distribution of occupied and unoccupied space was evaluated by the technique of Voronoi tessellation of space. The distributions of the Voronoi polyhedra volumes are very broad, and have a bimodal or a trimodal character, which is related to the structure of the polymer. Experimental values for the permeability of helium and carbon dioxide molecules were related to the fraction of Voronoi polyhedra with volumes > 10.5 Angstrom(3). The validity of the simulated polymer structures were further verified by comparison between the calculated values for the intersegmental spacings, and values measured by using X-ray diffraction. Copyright (C) 1996 Elsevier Science Ltd.