Syntheses of siloxane-grafted aromatic polymers and the application to pervaporation membrane

The syntheses of siloxane-grafted poly(amide-imide) and polyamide were carried out by a macromonomer method, in order to develop a highly permeable and durable membrane material for pervaporation. A novel compound, 3,5-bis(4-aminophenoxy)benzyloxypropyl-terminated polydimethylsiloxane (BAPB-PDMS), was synthesized as a macromonomer. BAPB-PDMSs with different PDMS segment lengths were prepared by hydrosilylation of 3,5-bis(4-nitrophenoxy)benzyl allyl ether with hydrosilyl-terminated PDMS using Pt catalyst, followed by hydrogenation reduction of the terminal dinitro groups. The polycondensations of BAPB-PDMSs with trimellitic anhydride chloride and terephthaloyl chloride yielded the desired siloxane-grafted poly(amide-imide) (PAI-g-PDMS) and polyamide (PA-g-PDMS) copolymers, respectively. The copolymer membranes were prepared by solvent-casting method, and the gas permeability and pervaporation property of these membranes were evaluated. As the solubility of the copolymers depended on the main chain structure, PA-g-PDMS membrane was insoluble in any solvents after it was dried in vacuo. The gas permeability coefficients of these copolymer membranes were increased as increase of PDMS segment length, and these values of PAI-g-PDMS were higher than those of PA-g-PDMS containing the same PDMS segment length. From the results of pervaporations of the dilute aqueous solutions of organic solvents, it was found that PA-g-PDMS exhibited the excellent permselectivity toward several organic solvents, such as alcohols, acetone, tetrahydrofuran, chloroform, dichloromethane and benzene with a high and stable permeation. Furthermore, it was confirmed that the removal of tetrahydrofuran from its dilute aqueous solution was efficiently achieved by the pervaporation using PA-g-PDMS membrane.