GAS-TRANSPORT PROPERTIES OF POLYCARBONATE POLYURETHANE MEMBRANES

Polyurethanes (PU) were prepared using polymeric diols, containing polar groups, as -O-C(O)-O- (carbonate) groups, carbonate and ether (-O-) groups, or carbonate and ester groups [-C(O)-O-]. PUs were prepared by the prepolymer two-step technique using ethyl acetate (EA) as the solvent; the diol was reacted at about +80-degrees-C with TDI (ratio 1:2) to give the prepolymer terminated with NCO, which was then cross-linked with triisopropanolamine (TIPA). The membranes were prepared using a Gardner knife and were characterized by differential thermal analysis (DSC). Most of the polymers prepared from low and medium molecular weight diols were amorphous and elastomeric at the temperature of gas transport measurement (35-degrees-C). The permeabilities (P) and the diffusion coefficients (D) of different gases (O2, N2, CO2, CH4, CO) were measured by a modified Lyssy apparatus, the solubility coefficient (S) was also calculated. The water-vapor transport properties D and S were measured according to ASTM. Diffusivity data follow the Fujita model and the solubility coefficients the regular solution theory, as developed by Prausnitz and Shair.