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Polyimide‐silica (PI‐SiO2) hybrids were prepared from a novel polyimide (PI), derived from pyromellitic dianhydride (PMDA), 1,6‐bis(4‐aminophenoxy)hexane (synthesized) and 4,4′‐oxydianiline. SiO2 networks (5–30 wt%) were generated through sol–gel process using either tetraethylorthosilicate (TEOS) or a mixture of 3‐aminopropyltriethoxysilane‐PMDA‐based coupling oligomers (APA) and TEOS. Thin, free standing hybrid films were obtained from the respective mixtures by casting and curing processes. The hybrid films were characterized using Fourier transform infrared, 29Si nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectrometry and atomic force microscopy (AFM) techniques. 29Si NMR results provide information about formation of organically modified silicate structures that were further substantiated by FE‐SEM and AFM micrographs. Contact angle measurements and thermogravimetric thermograms reveal that the addition of APA profoundly influences surface energy, interfacial tension, thermal stability and the residual char yield of modified hybrids in comparison to those obtained by mixing only TEOS. It was found that reduced particle size, efficient dispersion and improved interphase interactions were responsible for the eventual property enhancement. Copyright © 2012 John Wiley & Sons, Ltd.

Novel polyimide/γ-ray irradiated MWCNTs (PI/γ-MWCNTs) nanocomposites with improved dielectric properties were fabricated by casting and curing processes. The interfacial interactions between the two domains, i.e. PI and MWCNTs, were enhanced by hydrogen bonding between the hydroxyl groups present on PI and modified CNTs. A PI matrix having pendant phenolic hydroxyl groups was derived from pyromellitic dianhydride (PMDA) and diamine monomer 4,4′-diamino-4′′-hydroxytriphenylmethane. MWCNTs (5-20 wt%) were dispersed in the synthesized PI matrix. Before addition to PI, the surface of MWCNTs was equipped with hydroxyl and carboxylic groups by irradiating with γ-rays under a dry oxygen environment. Surface examination of PI/γ-MWCNTs composite films by scanning electron microscopy (SEM) revealed that MWCNTs are uniformly dispersed and completely wrapped by PI matrix, most likely due to the hydrogen bonding. The influence of greater adhesion of MWCNTs with PI matrix on the dielectric, visco-elastic, and mechanical properties of final PI/γ-MWCNTs nanocomposites was explored using appropriate analytical techniques. The composite films exhibited high dielectric constant, a 7.6 folds improvement as compared to pristine PI. The storage modulus (E′) and glass transition temperature (Tg) demonstrated an improvement of 1.4 and 1.2 folds, respectively. Similarly, mechanical and thermal properties were also found to be improved remarkably. We believe that significant property enhancement of PI/γ-MWCNTs nanocomposites is the direct consequence of increased interface compatibility via hydrogen bonding between polymer matrix and carbon nano-filler.