Studies on silicone‐grafted copolyimides, 3. Synthesis of soluble polyimide/polydimethylsiloxane graft copolymer and application to separation membrane

Abstract

AbstractPolyimide/polydimethylsiloxane (PI/PDMS) graft copolymer was prepared following the macromonomer method. First, 3‐(3,5‐diaminobenzyloxy)propyl‐terminated polydimethylsiloxane (DAB‐PDMS) was prepared by hydrosilylation of allyl 3,5‐dinitrobenzyl ether with hydrosilyl‐terminated PDMS, followed by catalytic reduction of the two nitro groups. PI/PDMS graft copolymer was synthesized by polycondensation of DAB‐PDMS with 4,4′‐oxydianiline (ODA) and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), followed by chemical imidation. The average degree of polymerization of the PDMS chain was in the range between 7 and 25. The resulting graft copolymers were soluble in several organic solvents. Membranes were prepared by solvent casting, followed by heating at 220°C in vacuo, upon which the membranes became hardly soluble in organic solvents. The gas permeability coefficients of the graft copolymer membranes were much greater than those of the polyimide homopolymer and of the same order as that of a PDMS membrane. Furthermore, a selective permeation of organic liquids, e.g., tetrahydrofuran, acetone and acetonitrile, was observed in the pervaporation of aqueous organic liquids through the copolymer membrane.