Bio-based monomers for UV-curable coatings: allylation of ferulic acid and investigation of photocured thiol-ene network

Ferulic acid (FA) is an unsaturated hydroxycinnamic acid that can be isolated from lignin. In this study, the biorenewable FA was allylated to result in a library of mono- or diallylated monomers, either having the inherent cinnamoyl double bond intact or saturated through hydrogenolysis. All monomers were photo-chemically cured with trimethylolpropane tris(3-mercaptopropionate) (TRIS) into crosslinked films in the presence of a photoinitiator (Irgacue 819). The reactivity of the FA-derived monomers toward TRIS was investigated in detail by photorheology and FT-IR spectroscopy to reveal details on the relative reaction rates for the different alkene groups. The thermo-mechanical properties of the crosslinked films were fully characterized by means of dynamic mechanical analysis (DMTA) and thermal calorimetry (DSC). It was demonstrated that the glass transition temperature of the final crosslinked network could be controlled by the addition of a monoallylated monomer. By increasing the content of the monoallylated compound, it was possible to observe a linear decrease of the Tg-values of the crosslinked films.