Polyurethanes containing Poly(arylene ether sulfone) and Poly(ethylene oxide) segments for gas separation membranes

Poly(arylene ether sulfone) and poly(ethylene oxide) (PEO)-based segmented polyurethanes were synthesized as potential gas separation membrane materials. Poly(arylene ether sulfone) oligomers with controlled molecular weights (15,000 and 20,000 g/mol M_n) were prepared with phenol endgroups by nucleophilic aromatic substitution step growth polymerization of 4,4'-dichlorodiphenylsulfone with a calculated excess of 4,4'-(propane-2,2-diyl)diphenol (bisphenol A). The oligomers with phenolic endgroups were subsequently reacted with ethylene carbonate to obtain aliphatic hydroxyethyl terminal functionality. The hydroxyethyl terminated polysulfone oligomers and hydroxy-terminated PEO were reacted with 4,4'-methylene diphenyl diisocyanate (MDI) to obtain segmented polyurethanes. Compositions with high poly(arylene ether sulfone) content relative to the hydrophilic PEO blocks were of particular interest due to their mechanical integrity. Size exclusion chromatograms confirmed that the polyurethanes had high molecular weights with unimodal molecular weight distributions. DMA and DSC thermograms revealed polyurethanes containing 30 wt % PEO have two distinct T_g's. Pure gas permeabilities of membranes were measured using a series of gases having different kinetic diameters including H₂, He, CO₂, O₂, N₂, and CH₄. Gas transport measurements showed changes in permeabilities as the PEO content in the polyurethane increased. The CO₂/N₂ and CO₂/CH₄ gas selectivity of membranes increased systematically as PEO content increased in the polyurethanes.