Modification of Epoxy Resins with Polyether-g-polysiloxanes

To improve the toughness of epoxy resin, and clarify the complex interrelationshipbetween the miscibility, morphology, toughness and composition of epoxyresin/graft copolymer blends, amphiphilic polysiloxane graft copolymers(F6-PMSs) with different contents of polyether were synthesized via hydrosilylationbetween epoxy-immiscible poly(methylhydrosiloxane) and epoxy-miscible allylpolyoxyethylene polyoxypropylene ether (F6) to modify diglycidyl ether of bisphenol A(DGEBA). The miscibility of amphiphilic graft copolymers with epoxy resin wasinvestigated by observing the transparency of the modified epoxies before and aftercuring and by detecting the glass transition temperature (Tg) of the cured epoxies usingdifferential scanning calorimetry. The morphologies of the cured epoxies were studiedby scanning electron microscopy, and the toughness in terms of tensile and impactstrength were examined by tensile and impact testing. Results indicated to highermiscibility of polysiloxane with DGEBA by grafting with polyether. Relative to the neatepoxy network, the polysiloxane modified epoxies exhibited lower Tgs and with theincreased polyether in graft copolymer, there was a decreasing trend noticed in Tg. Thenanostructures were obtained for the modified epoxies with different F6 to PMS ratios(5 wt% of DGEBA). The formation of the nanostructures in the thermosettingcomposites was judged by following the self-assembly and reaction-inducedmechanisms, mainly dependent on the miscibility of graft copolymer with epoxy resin.Moreover, toughness of the epoxy networks was greatly improved by F6-PMS of100/100 weight ratio at relatively low addition levels.