Allylation of a lignin model phenol: a highly selective reaction under benign conditions towards a new thermoset resin platform

Abstract

The lack of aromatic material constituents derived from renewable resources poses a problem to meet the future demands of a more sustainable society. Lignin is the most abundant source of aromatic structures found in nature and is a highly interesting source for material applications. Development of controlled chemical modification routes of lignin structures are crucial in order to further develop this area. In this study allyl chloride is used to selectively modify a lignin phenol in the presence of other lignin functionalities, i.e. aliphatic hydroxyls and conjugated alkenes, under mild reaction conditions in quantitative yields. For this, coniferyl alcohol was used as a model compound in the present study. The modification was carried out in ethanol as the synthesis media. Studies on the effect of reaction time and temperature revealed optimum conditions allowing for a quantitative yield without any detectable levels of byproducts as studied with NMR, FT-IR and FT-Raman. The thermal stability of the formed product was determined to be up to at least 160 °C through DSC measurements. In addition, as a proof of concept, the use of the allylated monomer to form crosslinked films using free radical thiol–ene polymerization was demonstrated.