Microstructure of epoxy resin grafted by polyurethane

Epoxy resins grafted by polyurethane (EP-g-PU) were prepared by reaction of NCO-terminated polyurethane prepolymer with epoxy resin. The effects of content of polyurethane and reactive diluter, diisocyanate structure on Tg and microstructure of cured EP-g-PU were investigated. The DSC results show that Tg of cured EP-g-PU increases with increasing content of polyurethane and decreases with increasing content of reactive diluter. The Tg of cured EP-g-PU derived from different diisocyanate is IPDI>MDI>TDI at the same conditions. The SEM results show that in fracture surface of cured EP-g-PU prepared by IPDI-polyurethane or MDI-polyurethane, epoxy resin is embedded by polyurethane to form a two-phase cell structure. Whereas, in fracture surface of cured EP-g-PU prepared by TDI-polyurethane, polyurethane as the island-phase is dispersed in epoxy resin phase to form an island-sea structure. But a two-phase cell structure of epoxy resin embedded by polyurethane is also observed in the island-phase.