Gas permeability of poly [1-(trimethylsilyl)-1-propyne] membranes modified by hexafluorobutyl methacrylate

Abstract

Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes have a very high oxygen permeability but a low separation factor for oxygen and nitrogen. Hexafluorobutyl methacrylate (HFBM) was incorporated into PTMSP membranes in order to increase the selectivity of the membrane for oxygen. HFBM was imbibed into the cast PTMSP membrane and polymerized by UV irradiation. The resulting membranes were not fully symmetrical; the chemical modification took place to a larger extent in the membrane volume closer to the UV light. The activation energy for the permeation of oxygen and nitrogen through the modified PTMSP membranes was determined to be positive. For HFBM modified PTMSP membranes, the higher the flux was, the lower the separation efficiency. Values of the permeability coefficient P for oxygen at 20°C, and of the separation factor for the modified membranes were: P(O 2)=1.39 × 10 −7 cm 3 (STP)-cm/cm 2-sec-cmHg, and P(O 2)/ P(N 2) = 5.4 for the sample with the highest separation efficiency, and P(O 2)=5.56 × 10 −7 cm 3 (STP)-cm/cm 2-sec-cmHg, and P(O 2)/ P(N 2) = 2.0 for the sample with the highest permeability. Both the unmodififed and HFBM modified PTMSP membranes showed no decline in P(O 2) and P(O 2)/ P(N 2) values over a period of six months.