Photocatalytic decarboxylation of diacids for the initiation of free radical polymerization

Abstract

Photopolymerization, which is one of the most attractive polymerization methods, has been recently studied for the development of new photoinitiators. Herein, we use a binary mixture of titanium dioxide (TiO₂) nanoparticles and carboxylic diacid as a novel photoinitiator to initiate the free radical polymerization of vinyl acetate (VAc). The polymerization of VAc is achieved both in aqueous medium and bulk. The initiation mechanism of TiO₂/diacids is studied via nuclear magnetic resonance (NMR) spectroscopy using ¹³C labeled diacids as probing molecules. Further, a universal reaction mechanism is established, where the polymerization of VAc is initiated by the HOOC-R˙ radical, which is generated from the photocatalytic decarboxylation of the diacid. The polymerization kinetics results indicate that the polymerization rate is strongly dependant on the diacid structure. Compared to the use of diacids with an odd number of carbons, it is found that using diacids with an even number of carbons results in the polymerization rate reaching the maximum value faster.