Preparation And Curing Properties Of Self-crosslinkable Unsaturated Polyesters

In recent years, the research of environment friendly thermosetting unsaturatedpolyesters received a lot of special attentions. Researchers tried to find somecross-linking monomers which have no toxicity instead of styrene, but, these kinds ofunsaturated polyesters usually have poor thermal resistance. In this paper, we tried tochange the traditional way of unsaturated polyesters’ curing process and prepareself-crosslinkable unsaturated polyesters in order to solve the environmental problemcaused by the volatile of cross-linking monomers.Two kinds of self-crosslinkable unsaturated polyesters were prepared: one isself-crosslinkable unsaturated polyesters with hydroxyl groups on branched chainswhile the other with double bonds on branched chains. The preparation process of theresins, mechanism of the self cross-linking reaction and the properties of the resinafter curing were investigated.1) Self-crosslinkable unsaturated polyesters with hydroxyl groups on branchedchains were synthesized through the polycondensation of maleic anhydride andglycidol. Investigation demonstrated that the unsaturated polyester resin could be selfcured through the addition reaction of pendant hydroxyl groups with the double bondson main chain when it was heated above150°C without additional cross-linkingmonomer. H-nuclear magnetic resonance (1H-NMR), Fourier transform infraredspectroscopy (FT-IR) and differential scanning calorimetry (DSC) were used tocharacterize. The results showed that self-crosslinkable unsaturated polyesters withhydroxyl groups on branched chains has excellent thermal resistance and mechanicalproperties.2) The preparation process and self-curing properties of the unsaturatedpolyesters with different raw material ratios were studied. The results showed that theunsaturated polyester resin turned into yellow hard solid after curing at150℃for2hours and post curing at180℃for4hours, two kinds of reactions were happened:the formation of ether bond by the addition reaction of hydroxyl to double bonds and ring opening reaction between epoxide and hydroxyl. With the increasing ofpolymerization degree, the conversion rate of double bonds in self crosslinkingreduced while the conversion rate of epoxide remained about the same.3) Self-crosslinkable unsaturated polyesters with double bonds on branchedchains was synthesized by the condensation reaction of acrylic acid and glycidolwhile the raw material ratios is3:1. The preparation process and self-curing propertieswere studied. Investigation demonstrated that this kind of unsaturated polyester resinturned into yellow hard solid after curing at100℃for2hours and post curing at120℃for2hours. Addition reaction happened between the double bonds on branchedchains. H-nuclear magnetic resonance (1H-NMR) and Fourier transform infraredspectroscopy (FT-IR) were used to characterize and the tensile properties of theunsaturated polyester resin after curing was tested. The results showed that theunsaturated polyester with double bonds on branched chains can be self cured and hasexcellent thermal resistance and mechanical properties.