PHYSICAL MODIFICATION OF POLY[1-(TRIMETHYLSILYL)-1-PROPYNE] MEMBRANESFOR GAS SEPARATION

Poly[1-(trimethylsilyl)-1-propyne], PMSP, has the highest gas permeabi lity of any synthetic polymer but exhibits a deterioration of these ga s permeability properties with time. A technique of blending PMSP with liquid poly(dimethylsiloxanes), PDMS, of different molecular weights was used to alter the decay in gas permeability properties of PMSP. So rption isotherms and permeability coefficient of CO2 were measured. Th e Langmuir capacity constant, C(H)', decreased with increasing content of PDMS in the membrane. Both the sorption and the permeability behav ior showed that modified membranes changed from a glassy state to a ru bbery state where the PDMS content of the lower viscosity liquids was larger than 40 wt%. PDMS of higher viscosity was more effective for de creasing of C(H)'. These results suggest that the filling of larger PD MS molecules occurred selectively in the larger microvoids rather than the smaller ones and the filling of smaller PDMS molecules occurred i n both the small and large microvoids in the PMSP membrane.