How can xanthates control the RAFT polymerization of methacrylates?

A xanthate bearing S-cyanoisopropyl and O-2,2,2-trifluoroethyl groups was identified as a potential RAFT agent for sequential polymerization of methyl methacrylate and vinyl acetate. The intrinsic low reactivity of the xanthate for MMA polymerization was compensated by implementing a semi-batch emulsion process with a thorough adjustment of the process parameters to keep MMA concentration to a minimum during polymerization. In a second stage, the xanthate-capped PMMA seed was chain extended during batch vinyl acetate polymerization at room temperature, yielding a well-defined PMMA-PVAc diblock copolymer.