Catalyst-Free Visible Light-Induced RAFT Photopolymerization

In contrast to thermoinitiated polymerization techniques, photoinitiated systems offer more attractive benefits, such as spatio-temporal control and polymerization rate control through a modulation of light intensity and wavelength. Until recently, there were very few living/controlled polymerization techniques which could be activated by visible light. In this contribution, we investigate the photolysis of different thiocarbonylthio compounds, including 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT), 4-cyanopentanoic acid dithiobenzoate (CPADB), and 2-(n-butyltrithiocarbonate) propionic acid (BTPA), under visible lights (typically, 5W) to initiate a reversible addition-fragmentation chain transfer (RAFT) polymerization. This is the first report which shows successful polymerizations of methacrylate monomers under visible LED light. Successful polymerization were obtained in the presence of CDTPA under blue and green LED light. A good control of the molecular weight as well as a low molecular weight distribution was achieved under green light.