Effects of bromine substitution on the physical and gas transport properties of five series of glassy polymers

The effects of bromine substitution on the physical and gas transport prope rties were examined for five families of tetra-substituted glassy polymers: bisphenol A polycarbonates (PC), hexafluoro-polycarbonates (HFPC), hexaflu orobisphenol-tertiary butyl isophthalates (HFBP-tBIA), fluorenebisphenol-t- butyl isophthalates (FBP-tBIA) and bisphenol A-t-butyl isophthalates (BPA-t BIA). Additionally, the thermal response of the substituted BPA-tBIA polyme rs was explored to elucidate the effects of bromine substitution on the act ivation energies of permeation and diffusion and on the heat of gas sorptio n. Compared to its methyl-substituted analog, each bromine-substituted poly mer had a higher cohesive energy density, a higher glass transition tempera ture and a lower oxygen-specific fractional free volume. Bromine substituti on significantly reduced O-2 and CO2 permeability and substantially increas ed both O-2/N-2 and CO2/CH4 selectivity. An increase in the activation ener gy of diffusion for N-2 compared to O-2, and for CH4 compared to CO2, may b e credited for the majority of the selectivity grain. A new method for eval uating penetrant-dependent fractional free volume proved to be a valuable t ool in determining the effects of structural changes on gas transport behav ior. (C) 1999 Elsevier Science Ltd. All rights reserved.