Synthesis and mechanical properties of unsaturated polyester-polyurethane IPN hybrids

Abstract

The IPN hybrids of unsaturated polyester (UPE) - polyurethane(PU) were prepared by the simultaneous polymerization process. The PU network was crosslinked with trimethylol propane (TMP) and the UPE network with styrene and divinyl benzene (DVB). The effect of the crosslink density of PU on the mechanical properties was investigated with the variation of amount of TMP. The tensile and impact properties were measured as a function of composition and degree of unsaturation of UPE. Enhanced tensile strength(79.8 MPa) and impact strength (27.3 J/M) were observed at the content of 20 wt.\% of PU. As the crosslink density of PU was increased, the tensile and impact strength were increased due to the increase of the degree of interpenetrating and grafting between two networks. When the degree of unsaturation of UPE is low, the crosslink density of PU had more influenced on the tensile properties andthe shift of $T_g$. This indicates that the crosslinking of polysyrene with UPE is restricted by the presence of PU because the grafting of UPE occurs at early stage of the reaction. It was suggested that the improved thermal stability was not directly related to the increase of physical entanglement but related to the unzipped monomers acting as radical scavengers for the radicals produced from the polyurethane degradation.