Visible and sunlight driven RAFT photopolymerization accelerated by amines: kinetics and mechanism

Recently, photochemical polymerizations have received interest since they can be performed under mild conditions and they offer temporal control over the reaction. In this study, the kinetics of photochemical dithiobenzoate-mediated RAFT polymerization in the presence of triethylamine is explored. This system uses mild light sources such as visible light and sunlight, and does not require the use of expensive or rare earth catalysts. Instead triethylamine is combined with reagents used in RAFT polymerization. This study investigates the effects of light source, RAFT chain transfer agent concentration, and amine concentration, to understand the kinetic contributions of each component and possible mechanism of this process. Data suggests that there is electron transfer from the amine to the excited RAFT end-group, which is the major radical generation pathway. Radicals are also generated directly from the excited RAFT end-group. This method yields living polymers as evidenced by the synthesis of well-defined block copolymers.