Photochemical synthesis of nitroxyl free radicals in the presence of vinyl monomers

Abstract The photochemical formation of an inhibitor in the presence of monomers and a photoinitiator offers the possibility of producing positive two‐step photoresists. As inhibitor precursor sterically hindred amines have been used in the presence of air oxygen and Rose Bengal as oxidation photosensitizer. On irradiation with visible light (546 nm). stable nitroxyle radicals are formed, which act as strong inhibitors of free radical polymerization. Hexanediol diacrylate and 2‐acryloxy‐2′‐propionyl oxydiethylether were used as monomers. The photoinitiator required for the second step polymerization is benzoin isopropyl ether, which photolyzes on irradiation at 340 n,. The quantum yield of nitroxyl radical formation has been determined in solution and in polymeric films. Polymerization inhibition experiments were carried out with methyl methacrylate in solution and with neat monomers. Though the quantum yield Φ NO° is low, especially in the last case, the experiments confirm the possibilities of this two‐step procedure.