| Abstract: | Polyurethanes (PU) based on poly(butylene adipate) [PU(PBA)] and poly(oxypropylene) [PU(PPG)] polyols have bean introduced into the diglycidyl ether of bisphenol A (epoxy) to form interpenetrating polymer networks (IPNs) with a PU-grafted epoxy structure (graft-IPNs). The tensile strength in both PU(PPG)/epoxy and PU(PBA)/epoxy systems increases with increasing PU content. Maximum values emerge at PU/epoxy ratios between 19/81 and 27/73. This is explained as a result of the presence of the graft structure, which leads to more intimate interpenetration between the PU and epoxy in the graft-IPNs. Dynamic mechanical analysis (DMA) indicates that the PU introduced can be incorporated in either the α or β transition domain of the epoxy. The tensile strength of the resulting graft-IPNs shows a significant improvement as the PU is incorporated in the α transition domain of the epoxy. It is also noted that suitable amounts of PU incorporated in both the α and β transition domains of epoxy can increase the tensile strength of the IPNs, while excessive amounts of PU introduced into both α or β transition domains tend to decrease the tensile strength of the graft-IPNs. |
