INSITU POLYMERIZATION OF TETRAETHOXYSILANE IN POLY(METHYL METHACRYLATE) - MORPHOLOGY AND DYNAMIC MECHANICAL-PROPERTIES

Dynamic mechanical spectroscopy and transmission electron microscopy were utilized to investigate the properties of composites resulting from the formation of a cross-linked inorganic network via the polymerization of tetraethoxysilane (TEOS) in situ in a poly(methyl methacrylate) (PMMA) binder. The results show that the morphology and physical properties obtained are governed by sample preparation and by the catalyst used to polymerize the TEOS; major differences are obtained when the polymerization of TEOS is performed in different pH regimes. The morphologies which develop are consistent with the known differences in gel structures obtained during the polymerization of TEOS in acidic or basic media. When TEOS is reacted under acidic conditions at elevated temperatures, small (< 100 angstrom) SiO2 domains which are well dispersed in the PMMA matrix result, producing a composite material with a high plateau modulus above the T(g) of PMMA which extends to at least 250-degrees-C. The time-temperature-transformation concept, proposed by Gillham for thermosetting organic polymers, is employed to explain some of these results.