Abstract
RAFT polymerizations of styrene with azobis(isobutyronitrile-α-13C) as initiator and various RAFT agents (cumyl dithiobenzoate (5), cyanoisopropyl dithiobenzoate (6), benzyl dithiobenzoate-thiocarbonyl-13C (7) or cyanoisopropyl dodecyl trithiocarbonate (8)) were followed by real time 13C NMR. While the rate of AIBN decomposition and the initial fate of the initiator-derived radicals (the initiator efficiency) were not substantially affected by the RAFT agent, the rate of polymerization was strongly dependent on both the type and concentration of RAFT agent. Polymerizations with the more active dithiobenzoate (5,6) RAFT agents and trithiocarbonate 8 display formation of a single unit styrene chain prior to any substantial formation of higher oligomers. An unexpected finding is the observation of 13C CIDNP for the ketenimine formed by cage recombination of AIBN-derived cyanoisopropyl radicals. With benzyl dithiobenzoate (7), consumption of the initial RAFT agent is slow. By-products from intermediate radical termination are also observed.
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