Thiol-ene coupling: An efficient tool for the synthesis of new biobased aliphatic amines for epoxy curing

Thiol-ene coupling interestingly allowed to synthesize reactive primary and multi-functional amines from renewable resources with high yield and in mild conditions. These syntheses were performed in two steps from triallyl pentaerythritol (PE-Al) by esterification of the hydroxyl function with a long or medium alkyl chain and thiol-ene coupling with the cysteamine hydrochloride on the allyl functions. The first step, the esterification allowed to fix a hydrophobic chain giving the water-insoluble characteristic to the future amine to increase the yield of the extraction after amination by thiol-ene reaction. The second step, the thiol-ene coupling was realized under UV initiation with excellent yields. The synthetized multifunctional amines were used as hardeners with different aromatic biobased epoxy matrix: the phloroglucinol tris epoxy (PGTE) and the diepoxydized cardanol (NC-514). A traditional petroleum-based epoxy matrix, bisphenol A diglycidyl ether (BAGDE), was also used for comparison and to precise the functionality of synthetized amines. Glass transition temperatures of each epoxy network are evaluated from 10 °C for the NC-514 networks to 100 °C for the PGTE networks and the thermal stability was also studied by thermogravimetric analysis.