Network density control in epoxy–silica hybrids by selective silane functionalization of precursors

Following previous work on the compatibilization of organic–inorganic hybrids through coupling reactions with the precursor components, the present study evaluates the relative efficiency of different types of coupling agents on the morphology and properties of epoxy–silica hybrids. In particular, this investigation compares the effects of introducing trialkoxysilane functional groups at the chain end (using amine‐ and mercapto‐silanes) with similar types grafted in the middle of the chain of the constituent resin (using an isocyanate silane). The use of coupling agents with a basic character (amine silane type) brings about the formation of denser networks in both constituent phases of the resulting epoxy–silica hybrid, which is manifest through a large increase in the Tg and a more extensive suppression of the molecular relaxations within the glass transition regions. Increasing the number of alkoxysilane functional groups at the chain end, with the use of a bis‐aminosilane, has a relatively minor effect on the morphology and dynamic mechanical spectra of the resulting epoxy–silica hybrids. It was also found that while the incorporation of small amounts of a high molecular weight epoxy resin causes considerable plasticization of the organic phase, much larger amounts of organic (aliphatic) co‐agent within the siloxane phase are required to deteriorate those properties that are related to the inorganic character of the hybrid material.