Gas transport in modified polysulfones with trimethylsilyl groups: effect of substitution site

Trimethylsilyl (TMS) groups were chemically introduced on to the phenylene group of bisphenol-A polysulfone (PSf) at sites ortho to ether (EM3) or to sulfone (SM3) linkages. Gas permeabilities increased by substitution of TMS and especially oxygen permeability increased from 1.1 barrer for PSf to 4.2 barrer for SM3 and to 7.1 barrer for EM3. Perm-selectivity of oxygen to nitrogen decreased from 5.8 to 5.5 and therefore substitution of TMS on polysulfone resulted in improved gas transport properties. In addition, it was found that EM3 is more effective in enhancing the gas transport properties than SM3. In order to interpret the effect substitution site on gas transport, d-spacing was investigated in terms of interchain packing. Furthermore, the effect of substitution site on chain motion was investigated through dynamic mechanical analyzer (DMA), dielectric analyzer (DEA), and solid-state NMR. DMA and DEA experiments showed that motions of unsubstituted phenylene and sulfonyl linkage are much more hindered in SM3 than in EM3. NMR experiments showed that motion of TMS is more mobile in EM3 than in SM3. These results revealed that chain motions of SM3 are more hindered than those of EM3 and substitution site affects chain motions. Therefore, we can conclude that these changes in chain motion also gas transport in modified polysulfones with silyl side group.