Abstract
The non-hydrolytic sol-gel process has been used for the synthesis of ORganically- MOdified SILicas (ORMOSILs). The effect on morphology of the ormosil particles has been investigated using different solvents, types of stirring, and additives such as surfactants or polystyrene. Dimethyl sulfoxide has been used as a novel oxygen donor for the catalyst-free formation of colourless silsesquioxanes. The products are organic- inorganic hybrid (nano)composite materials where the organic modifications (methyl, ethyl, hexyl or phenyl groups) are covalently attached to silicon. Spherical particles of ca. 1 mum diameter were obtained in the non-hydrolytic sol-gel synthesis of methyl-modified silicate particles under certain conditions such as using BrijRTM 52 as surfactant and using DMSO as oxygen donor. Product yields were generally high, and the products were characterised by Fourier transform infra-red (FT-IR) spectroscopy, 29Si nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and elemental analysis (EA). Selected ormosils were used as additives to an epoxy resin system (XLVR16-2) .as toughening agents. Compatibility of the hybrid with the epoxy was varied by changing the nature of the organic group in the hybrid. The ormosil additives were uniformly dispersed throughout the resin matrix. The fracture toughness of the resin was improved using 5 parts per hundred of the resin of ethyl-modified silicate (50 % greater than that of the unmodified resin) maintaining the excellent thermal properties of the system. Epoxy resin systems were characterised by SEM, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and fracture toughness testing. Emulsion polymerisation of polyhedral oligomeric silsesquioxanes (POSS) with methacrylate functionalities covalently attached to them was also investigated. Two types of polymerisation were carried out: homopolymerisation of POSS monomers, and copolymerisation of POSS monomers with methyl methacrylate (MMA) at different molar ratios, which lead to spherical nanoparticles ranging from ca. 5 to 15 mm in diameter.