New bio-based polymeric thermoset synthesized by ring-opening polymerization of soybean oil-based resin with green curing agent

Renewable resources, such as vegetable oils, woody biomass and terpenes, have attracted a great deal of attention in polymer synthesis [1, 2]. As one of the most important derivatives from rosin, the maleopimaric acid (MPA) is a fascinating choice to be a green curing agent for epoxy. In our study, MPA was successfully synthesized between abietic acid (AA) and maleic anhydride (MA) by using the catalyst p-toluene sulfonic acid[3]. The optimal experiment was conducted at 1:1.1 molar ratio of AA to MA and 190℃ in an airtight reactor for 2h. The chemical structure and properties of the product were characterized in detail by FT-IR, DSC, 1H NMR and 13C NMR, which indicated that MPA with high purity could be synthesized through the isomerization of AA to levopimaric acid (LA) following by Diels-Alder reactions between LA and MA. And then, a new bio-based polymeric thermoset was developed by the ring-opening polymerization of epoxidized soybean oil (ESO) with MPA catalyzed by 2-ethyl-4-methylimidazole (EMI)[4]. The curing was performed at 160℃ for 2h and 180℃ for 1h in a vacuum oven. The curing behaviors and the properties of the polymeric thermoset were studied with a comparison of a commercial curing agent, methylhexahydrophthalic anhydride (MHHPA). The epoxidized soybean oil cured by MPA can be used for various industrial applications not only due to its similar thermal and mechanical properties to that cured by the commercial curing agent but also the extra potential biodegradability