MECHANICAL-PROPERTIES OF POLYURETHANE-UNSATURATED POLYESTER INTERPENETRATING POLYMER NETWORKS

Interpenetrating polymer networks (IPNs) based on a polyurethane (PU) and two unsaturated polyester (UPE) resins (a commercially available U PE and a partially endcapped UPE) were prepared. The mechanical proper ties, such as tensile strength, elongation at break, impact strength, and dynamic mechanical properties of IPNs, were studied by changing re action temperature, PU reaction rate, and UPE reaction rate. Owing to the unique microgel formation of UPE, the first formed network tends t o be the dispersed phase in the PU-UPE IPN system. The reaction sequen ce was found to be an important factor in determining the phase mixing and phase morphology of the IPNs. When the PU reaction was faster, ex tensive phase mixing due to strong grafting or chain interpenetration was obtained. When the UPE reacted first, grafting was retarded by the microgel formation of the UPE network. It was found that simultaneous reaction of the two reacting system resulted in a co-continuous struc ture that provided enhanced tensile properties and impact strength.