Quercetin allylation and thiol–ene click photopolymerization to produce biobased polymer thermosets with robust thermomechanical properties

Abstract

The development of biobased and functionalized monomers along with eco-friendly photopolymerization processes represent promising methods for the development of renewable and more environmentally friendly thermosets. Thiol–ene ‘click’ photopolymerization is particularly advantageous in this regard; however, the materials derived from this method often exhibit low glass transition temperatures (T_g) and unsuitable thermomechanical properties for applications at room temperature. Herein, we report the synthesis of biobased allyl derivatives from quercetin, a renewable flavonoid compound widely available in fruits, vegetables and plants. We demonstrated the isolation of tetra- and penta-allylated quercetin (Q1 and Q2, respectively) and their subsequent photoactivated thiol–ene polymerization. By introducing a biobased thiol curing agent (PTTMP) derived from glycerol and mercaptopropionic acid, we produced fully biobased crosslinked thermosets with high content of aromatic moieties provided by the framework of the monomers. Real-time infrared spectroscopy showed the effective thiol–ene photopolymerization of Q1 and Q2 and PTTMP with conversions of 60% and 75%, respectively, after 15 min of UV irradiation. Due to the modulated crosslinking degree from the allyl group functionalization in the monomers, the biobased crosslinked networks showed storage moduli from 420 to 739 MPa, thermal stability from 220 to 257 °C and T_g values ranging from 75 to 90 °C. This work outlines straightforward strategies for creating biobased thermosets that overcome the limited thermomechanical properties of thiol–ene networks and offer potential antimicrobial and antioxidant properties. © 2024 Society of Chemical Industry.