New copolyimide membranes with high siloxane content designed to remove polar organics from water by pervaporation

The syntheses of oligodimethylsiloxane film forming materials and their organoselective properties for the removal of ethanol and phenol from water by pervaporation are reported. Two series of segmented polydimethylsiloxane-imide (PSI) copolymers were synthesized from α,ω-(bisaminopropyl) dimethylsiloxane oligomers (ODMS) and aromatic dianhydrides (PMDA, 6FDA); synthesized PSI were obtained with a high content of siloxane block, i.e. up to 94 wt.%. To improve the average molecular weight of siloxane copolymers prepared from the longer chain length ODMS, the particular extender 1,3-bis(3-aminopropyl) tetramethyldisolxane (MDMS) was used, giving thus materials with enhanced mechanical properties. Pervaporation (PV) results showed that the PSI led to a selective recovery of the organic compounds from their aqueous mixtures. The structure-properties relationships of these materials are discussed with respect of polydimethylsiloxane-imide microstructures, taking into account especially the dianhydride type and the chain length of the oligomers used. PSI having a high amount of siloxane blocks gave the best PV results and optimum pervaporation performances were obtained with membranes incorporating aromatic fluorinated residues (feed=5 wt.% PhOH: α=22 and J10μm=2.4 kg/m2 h/feed=10 wt.% EtOH: α=10.6 and J10μm=0.56 kg/m2 h).