The observation of photo-Kolbe reaction as a novel pathway to initiate photocatalytic polymerization over oxide semiconductor nanoparticles

Polymerization of vinyl acetate is achieved under the photocatalysis of TiO2 nanoparticles in aqueous suspensions. It is clarified that the photocatalytic polymerization is due to the acetic acid generated from the hydrolysis of vinyl acetate. 13C NMR analysis further demonstrates by using 2-13C-acetic acid that vinyl acetate is initiated by methyl radical that results from the photo-Kolbe reaction. This result reveals a new function of the photo-Kolbe reaction as a pathway to realizing photocatalytic polymerization. A free radical chain mechanism is established for the polymerization. Kinetics studies show that the rates of initiation increase with the amounts of acetic acid added increasing. If the vinyl acetate aqueous solution is replaced by a vinyl acetate bulk, no polymerization is detected under the identical irradiation condition. This difference is correlated with the acid–base equilibria of the TiO2 nanoparticles and the anionic CH3COO− from the ionization of acetic acid.