Interpenetrating polymer networks of polyurethane and graft vinyl ester resin: polyurethane formed with toluene diisocyanate

For enhancing the compatibility and/or the interpenetration of the simultaneous interpenetrating networks (SINs) composed of polyurethane (PU) formed with toluene diisocyanates (TDI) and vinyl ester resin (VER) in which there were no chemical bonds between the two networks, a series of well-defined graft VERs consisting of different side chains were synthesized and characterized. The side chains existing in such graft VERs were formed from TDI and butanol (called BO-g-VER) or poly(oxypropylene) with different molecular weights (Mw: 200 and 390, called 200-g-VER and 390-g-VER, respectively). Differential scanning calorimetry measurements and the scanning electron microscopy observation indicated that the morphology of graft VERs had a great effect on the interpenetration and/or the compatibility between the two networks for PU/graft VER SIN systems. The SIN consisting of 200-g-VER exhibits excellent interpenetration between the two networks, as 200-g-VER network is a compatible system. For SIN composed of BO-g-VER, the compatibility between the two phases is greatly improved, since there are more content of urethane groups existing in grafts which should mix well with those in the PU network. Thus, the mechanical properties increase appreciably with the increase of graft VER content for these two SIN specimens. However, the reinforcement effect of 390-g-VER network on PU network is poor, as such a SIN shows a serious phase separation due to the micro-phase separated morphology of 390-g-VER network’s own self.