Diazonium salts for surface-confined visible light radical photopolymerization

The surface chemistry of aryl diazonium salts has progressed at a remarkable pace in the last two decades, and opened many avenues in materials science. These compounds are excellent coupling agents for polymers to surfaces via several surface-confined polymerization methods. For the first time, we demonstrate that diazonium salts are efficient for surface initiating radical photopolymerization in the visible light of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) taken as model monomers. To do so, 4-(dimethylamino)benzenediazonium salt was electroreduced on gold plates or flexible ITO sheets to provide 4-(dimethylamino)phenyl (DMA) hydrogen donor layers; while excited state camphorquinone acted as the free hydrogen abstractor. In the same way, we co-polymerized HEMA and MMA with ethylene glycol dimethacrylate in order to obtain crosslinked polymer grafts. We demonstrate by XPS that gold was efficiently screened by the polymer layers and that the wettability of the surfaces accounts for the hydrophilic or hydrophobic characters of the tethered polymers. Homo- and crosslinked PMMA grafts were found to resist removal by the paint stripper methyl ethyl ketone. The grafted DMA/camphorquinone system operating in the visible light holds great promises in terms of adhesion of in situ designed continuous or patterned polymer coatings on various substrates.