Formation and structure of the epoxy-silica hybrids

The organic-inorganic hybrid interpenetrating network (TPN) composed of an epoxide-amine network and silica was prepared and studied. Formation of the inorganic phase from tetraethoxysilane (TEOS) by sol-gel process was characterized by Si-29 n.m.r. spectroscopy, gas chromatography, small-angle X-ray scattering and electron microscopy. Kinetics of the silica structure build-up in the organic matrix, its final structure and morphology depend on the method of IPN hybrid preparation. The large compact silica aggregates, 100-300 nm in diameter, are formed during the one-stage polymerization. The two-stage process with the acid prehydrolysis of TEOS leads to an acceleration of gelation and formation of more open and smaller silica structures: 50-100 nm in diameter. The most homogeneous hybrid morphology with the smallest silica domains of size 10-20 nm, appears in the sequential IPN. The development of the silica structure is restricted by a rigid reaction medium of the preformed epoxide network. (C) 1998 Elsevier Science Ltd. All rights reserved.