Microstructural investigation of dense membranes in relation to their gas transport properties

The morphology together with the gas permeation properties of crosslinked membranes prepared from different amounts of a polyorganophosphazene −(−NP(R1)0.18(R2)0.76(R3)1.06−)n−−(−NP(R1)0.18(R2)0.76(R3)1.06−)n− where R1 = 2-allylphenoxy, R2 = 4-isobutylphenoxy and R3 = 4-methoxyphenoxy (M¯w=1,350,000 g/mol) and a hydride terminated polydimethylsiloxane M¯n=14,400 g/mol were investigated. The microstructure of some resulting films was first examined by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The transport properties of the films were second examined with respect to their permeability to light gases such as He, H2, O2, N2 and CO2, and selectivity ratios were established. Different theoretical copolymer permeability models were tested as a function of the chemical composition to investigate the relationship between morphology and permeation properties and to give a complete insight into the copolymer morphology. Selectivity ratios are discussed as a function of the penetrant nature and of the copolymer structure.