New biobased epoxy hardeners: Thiol-ene addition on oligobutadiene

We report the synthesis and characterization of oligobutadienes functionalized with primary amine groups and theirs use as hardeners for epoxy resins. The functionalization of polybutadiene (with 59% of 1,2 double bonds) was carried out by the addition of 2-amino-3-mercaptopropanoic acid (cysteamine) in different ratios through thiol-ene coupling. The thiol-ene addition was performed in tetrahydrofurane solvent with 2,2′-azobis(2-methylpropionitrile) as radical initiator at 70 °C. The ratio polymer/cysteamine was varied in order to obtain several number of amine functions per polymer chain and to compare the reactivity of thiol onto 1,2 and 1,4 double bonds of polybutadiene. The different characterizations of synthesized polymeric amines allowed us to identify the quantities of amine groups grafted onto 1,2 and 1,4 double bonds, the cyclization side reactions of 1,2 double bonds and the unreacted 1,2 and 1,4 double bonds. These polymeric amines were mixed with epoxy resins (BADGE) and led to materials with glass transition temperatures between 20 °C and 60 °C depending on the polymeric amines functionalities. The thermal properties of synthesized resins are similar to the ones measured on epoxy resins obtained with commercial hardeners (cycloaliphatic amine and 1,10-diaminodecane).