Original Bio-Based Antioxidant Poly(meth)acrylate from Gallic Acid-Based Monomers

Herein, we report a multistep synthesis of novel (meth)acrylate monomers based on gallic acid (GA), a biosourced phenolic acid. The objective of this work was to obtain bio-based polymers exhibiting antioxidant properties provided by monomers derived from gallic acid. The phenolic groups of GA, which are responsible for antioxidant properties, need to be protected for two reasons. On the one hand, functionalization to transform GA into polymerizable monomers must not take place at the phenolic groups because they must remain free to maintain the maximum antioxidant activity in the final polymers. On the other hand, their protection is necessary to prevent radical scavenging during the radical polymerization. After synthesis of such monomers, protected GA-based polymers were thus produced through a photo-mediated RAFT polymerization at room temperature by evaluating two trithiocarbonate-type chain transfer agents (CTAs). The kinetics and molecular weight distributions were studied depending on the monomers and the CTAs. Protected polymers were then deprotected to afford polymeric chains carrying one free gallic acid moiety on each monomer unit. The antioxidant activity of these free GA-based polymers was demonstrated either through the DPPH free radical scavenging property or through the inhibition of methyl linoleate oxidation.