Gas transport properties of polyimides (PIs) and their silica hybrids were investigated. The PIs synthesized with several methyl-substituted phenylenediamines were hybridized with silica via a sol-gel process with different alkoxysilanes. The prepared hybrid membranes showed controlled gas permselectivity, depending on the selected phenylenediamines and alkoxysilanes. It was worth noting that the hybrids prepared with tetraethoxysilane possessed improved CO(2)permselectivity with increasing silica content, which tended to exceed the upper-bound trade-off line. This fact suggested the additional formation of free volume holes especially favorable for the CO2/CH(4)separation around the polymer/silica interfacial area.
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