Reinforcement of crosslinked rubbery epoxies by in-situ formed silica

Rubbery crosslinked epoxide was reinforced with silica-siloxane structures formed in situ by sol-gel process from tetraethoxysilane. The increase in m odulus by two orders of magnitudes was achieved at a low silica content (<1 0 vol%). Various polymerization procedures including simultaneous or sequen tial formation of the epoxide network and silica resulted in different stru ctures of the microphase separated organic-inorganic hybrid composite. Stru cture and morphology of the heterogeneous system were analyzed by electron microscopy and small-angle X-ray scattering. Temperature dependences of sto rage modulus and loss factor were used to evaluate phase structure of the h ybrids and the interaction between epoxy and silica phases. Efficiency of t he reinforcement depends on the reaction conditions; a crucial effect of an interphase formation is shown. Acid catalysis of the sol-gel process proba bly promotes grafting between epoxide and silica phases and leads to a more uniform and finer structure with smaller silica domains. Comparison of the mechanical data with the theoretical models reveals that studied composite s correspond to the morphological model of the hybrid consisting of co-cont inuous epoxy and silica structures. (C) 1999 Elsevier Science Ltd. All righ ts reserved.