Preparation and characterization of novel polyimide-silica hybrids

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 (5-30wt%) 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. © 2012 John Wiley & Sons, Ltd.

Synthesis and characterization of novel coatable polyimide-silica nanocomposites

We report synthesis of a novel diamine 1,2-bis(4-(Hydrazonomethyl)phenoxy) ethane (bis- HPE) and a derived novel polyimide. The diamine was reacted with PMDA and ODA to synthesize copolyimide. Unmodified and modified silica particles were dispersed in the polyimide to prepare polyimide-silica hybrids: (a) unmodified (PSH-UM), and (b) modified (PSH-M). The PSH-UM were prepared by generating silica particles in situ in PI. In PSH-M, structural group identical to PI, 2,6- bis(3-(triethoxysilyl)propyl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)- tetraone was introduced into silica nano-particles. The structural similarity enhanced compatibility between organic-inorganic components by like-like chemical interactions as both contain flexible alkyl groups. PSH-M have shown improved surface smoothness, hydrophobicity and thermal stability. Such properties are mandatory for stable coatings. The structure of silica and PI was affirmed by FTIR, EDX, and solid-state 29Si NMR spectroscopy. Morphological and thermal properties of the prepared PI-SiO2 nano-composites were investigated by field emission scanning electron microscopy, atomic force microscopy, contact angle measurement and thermogravimetric analysis. © 2013 Springer Science+Business Media Dordrecht.

Development of novel coatable compatibilized polyimide-modified silica nanocomposites

A series of novel coatable polyimide silica (PI-SiO2) nanocomposites have been synthesized. A new PI matrix, containing pendant hydroxyl groups, was prepared reacting diamine monomers (4,4'-diamino-4"- hydroxytriphenylmethane, and 4,4'- oxydianiline) and pyromellitic dianhydride (PMDA). Whereas, silica reinforcement was generated using TEOS. A coupling oligomeric species 2,6-bis(3-(triethoxysilyl)propyl)pyrrolo[3,4- f]isoindole-1,3,5,7(2H,6H)-tetraone (APA) was used to furnish silica nanoparticles with imide linkages and hydroxyl groups. As these groups are already present in PI matrix, so their presence in nanoparticles brought structural similarity, and hence enhanced phase connectivity among two phases. The resulting PI-SiO2 hybrids, with improved interfacial interactions through hydrogen bonding and like-like chemical interactions, displayed much enhanced morphological, thermomechanical, and thermal properties. The properties of resulting hybrids were studied by various advanced techniques and compared with PI-SiO2 hybrid system which was prepared from same polyimide and unmodified silica network.© Springer Science+Business Media Dordrecht 2014.