Preparation of polyimide/polydimethylsiloxane graft copolymer and its permeabilities for gases and liquids

Polyimide/polydimethylsiloxane (PI/PDMS) graft copolymers with various PDMS contents were prepared by polycondensation of PDMS macromonomer 1 with aromatic diamines and pyromellitic dianhydride followed by heating at 220°C. The PDMS content of the grafts copolymers was controlled by changing the average degree of polymerization of the PDMS macromonomer in the range between 4 and 21. Graft copolymer membranes were prepared by casting films in the poly(amic acid) stage 2 and subsequent imidation upon heating. PI/PDMS membranes thus obtained are insoluble. The permeability coefficients towards nitrogen, oxygen, hydrogen, methane and carbon dioxide were evaluated. In the region of a PDMS content above 50 wt.-%, the oxygen permeability coefficient of a PI/PDMS graft copolymer membrane is > 10−8 cm3(STP) · cm · cm−2 · s−1 · cmHg−1. In addition, the permeability coefficient of methane is remarkably enhanced in comparison with a PI membrane. Preferential permeation of ethanol was observed through the graft copolymer membrane in the case of pervaporation of aqueous ethanol solution. Furthermore, acetone, acetonitrile and tetrahydrofuran were efficiently separated from water at any solvent/water ratio in the mixture.