An investigation of physico-chemical properties of a new polyimide–silica composites

Abstract

In the present study, a novel diamine 1,4-bis[4-(hydrazonomethyl)phenoxy]butane (4-BHPB) has been successfully synthesized by a facile method. 4-BHPB was reacted with pyromellitic dianhydride (PMDA) to derive a novel polyimide (PI). Highly compatibilized PI–SiO₂ nanocomposites were tailored using synthesized PI matrix and modified silica nanoparticles. The compatibility between organic–inorganic (O–I) components was remarkably improved by charge transfer complex (CTC) formed between PI chains and modified silica nanoparticles. PI chains have electron donor and acceptor groups (diamine and dianhydride portion, respectively). These groups were generated in silica nanoparticles by the organic modification through 2,6-bis(3-(triethoxysilyl)propyl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone (M-SiO₂), which in turn, was prepared reacting PMDA with 3-aminopropyltriethoxysilane. Sol–gel method was used for in situ synthesis of silica nanoparticles from a mixture of M-SiO₂ and TEOS. The enhanced compatibility between O–I phases through CTC formation furnished PI–SiO₂ nanocomposites (designated as OI-M) with improved thermal stability, hydrophobicity, and surface smoothness. For the comparison of properties, another series of PI–SiO₂ composites (OI-UM) were prepared dispersing unmodified silica micro-particles into PI matrix. OI-UM hybrid system does not contain CTC between PI matrix and silica particles. The structure of the monomer, PI, and organically modified silica network was analyzed by FTIR, and NMR spectroscopy. Thermogravimetric analysis, FE-SEM, contact angle measurement, and AFM were used to study thermal and morphological properties of the synthesized PI–SiO₂ hybrids.