Reversible addition-fragmentation chain transfer cyclopolymerization of dimethacryloyl open-cage silsesquioxane

We recently reported a bifunctional methacrylate monomer having a side-opened cage-silsesquioxane as a scaffold. Although free-radical polymerization proceeded mainly through cyclopolymerization, cross-linking structures were included. In this work, we have optimized the reaction conditions for reversible addition-fragmentation chain transfer cyclopolymerization using 2-cyano-2-propyl dithiobenzoate. As a result, polymers with relatively low polydispersity indices were successfully obtained. After removal of dithiobenzoate end groups, the transparency was high (>98%) in the range of visible range (400-800 nm). The content of the unreacted dangling vinyl groups, which was controlled by monomer concentration, affected the thermal stability of the resulting polymers. In addition, the bifunctional cage-silsesquioxane monomer can be readily copolymerized with methyl methacrylate without cross-linking.