Preparation and properties of epoxy resin modified with polyurethane based on hexamethylene diisocyanate and different polyols

Polyurethanes (PURs) synthesized using hexamethylene diisocyanate (HDI) and polyethylene glycol with molecular weights of 400 g mol(-1) and 600 g mol(-1) (PUR 400 HDI and PUR 600 HDI) or polyoxypropylene diol (POPD) of molecular weights 1002 g mol(-1) and 2002 g mol(-1) (PUR 1002 HDI and PUR 2002 HDI) were used as modifiers for diglycidyl ether of bisphenol A. It was found that maximum improvement in impact strength and critical stress intensity factor (K-C) values was obtained for compositions containing 15% PUR 400 and 5% PUR 1002. Such improvement in the resistance to crack propagation due to PUR incorporation might be related with the soft segments of polyethylene glycol and POPD. The critical stress intensity factor (K-C) values increased from 1.7 MPa m(1/2) (virgin epoxy) to 2.5 MPa m(1/2) with the addition of 10% PUR 400. Fourier transform infrared spectra confirmed the formation of an interpenetrating polymer network structures with polymeric modifier. Scanning electron micrographs of epoxy resins (EPs) modified with PUR with longer chains (PUR 1002 and PUR 2002) exhibited a deformed leaf-like morphology with larger plastic deformation zones with the presence of microcracks. However, EP/PUR based on polyethylene glycol showed less deformed structure.