Effect of Silanes on the Morphology, Hydrophobicity, and Dynamical Mechanical Properties of Polyimide/Silica Hybrid Membranes

Polyimide (PI)/silica hybrid membranes with high contact angles were prepared through the in situ sol-gel process. The precursor, poly(amic acid) with controlled block chain length, was synthesized using 4,4'-diaminodiphenyl ether (ODA), 3,3',4,4'-benzophenone-tetracarboxylic dianhydride (BTDA) and 3-aminopropyl-trimethoxysilane (APrTMOS) or 3-aminopropyldimethylethoxysilane (APDiMOS). And then, phenyltrimethoxysilane (PTS) or tetramethoxysilane (TMOS) or methyltrimethoxysilane (MTrMOS) was respectively, added to the above polyamic acid and mixed thoroughly. Following curing reaction, the PI/silica hybrid membranes with different cross-linkages, silica content, and hydrophobic properties were prepared. The effect on the formation of PI imide ring during imidization reaction is increased as the increase of silanes content and characterized by frequency shiftment and absorbance ratio of Fourier transform infrared (FTIR) measurements. All the hybrid membranes show high transparency though with high silica contents. The storage modulus, tan delta, and damping intensity by DMA measurements are all correlated with silane content or block chain length. And all these membranes with silane content possess high contact angle as compared to pure PI without any silanes added and the contact angles increase with increasing the silane content. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 648-656, 2011