Investigation into the photolytic stability of RAFT agents and the implications for photopolymerization reactions

The photolytic stability of various RAFT agents (i.e., thiocarbonylthio-containing compounds) under irradiation from a blue LED light source has been investigated. The effect and implications of efficient photo-fragmentation and potential photo-degradation with regard to their performance in photopolymerization reactions is reported. The stability is found to depend strongly on the structure of the fragmenting (R-) group and the reactivity of the carbon-centered radical formed following photolytic cleavage. This is proposed to be due to the competitive rates of radical recombination and thiyl radical degradation, and has implications on the choice of monomer (as monomer propagation requires re-initiation of the oligomeric/polymeric RAFT agent). These findings can provide guidelines and increase understanding when conducting a photopolymerization employing thiocarbonylthio RAFT agents.