Ab-Initio-Based Kinetic Modeling to Understand RAFT Exchange: The Case of 2-Cyano-2-Propyl Dodecyl Trithiocarbonate and Styrene.

Ab-initio-calculated rate coefficients for addition and fragmentation in reversible-addition fragmentation chain transfer (RAFT) polymerization of styrene with 2-cyano-2-propyl dodecyl trithiocarbonate initiated by azobisisobutyronitrile allow the reliable simulation of the experimentally observed conversion, number average chain length, and dispersity. The rate coefficient for addition of a macroradical Ri to the macroRAFT agent Ri X at 333 K (6.8 104 L mol-1 s-1 ) is significantly lower than to the initial RAFT agent R0 X (3.2 106 L mol-1 s-1 ), mainly due to a difference in activation energy (15.4 vs 3.0 kJ mol-1 ), which causes the dispersity to spike in the beginning of the polymerization.