RAFT for the Control of Monomer Sequence Distribution - Single Unit Monomer Insertion (SUMI) into Dithiobenzoate RAFT Agents

In this paper we explore RAFT (reversible addition-fragmentation chain transfer) single unit monomer insertion (SUMI) into dithiobenzoates. Styrene and N-isopropylacrylamide (NIPAm) were successfully inserted into 2-cyanopropan-2-yl dithiobenzoate. Attempted SUMI of methyl methacylate (MMA) provided an oligomeric insertion product due to the low transfer constant of the dithiobenzoate in MMA polymerization. A very low yield with maleic anhydride (MAH) reflects the low reactivity of MAH towards 2-cyanopropan-2-yl radicals. We also examined insertion of MAH, styrene and NIPAm into the styrene SUMI product. Insertion of MAH was rapid and efficient. SUMI with styrene and NIPAm was slower, which is attributed both to the low monomer concentrations used and the poor leaving group ability of the propagating species. The reaction with NIPAm is additionally complicated by initiator-derived by-products.