Quantitatively Probing Cross-Termination in RAFT Polymerization by an Externally Applied Magnetic Field

Cross-termination in bulk reversible addition-fragmentation chain transfer (RAFT) polymerization is characterized by defining a new parameter, R-M, in terms of the polymerization rates with and without an externally applied magnetic field (EAMF). For the bulk RAFT polymerization (RAFTP) of styrene (St), mediated by (2-cyano-2-propyl)dithiobenzoate (CPDB) and S-1-dodecyl-S-(, -dimethyl--acetic acid)trithiocarbonate (DDMAT), an R-M of 0.534 and 0.382 is obtained respectively, showing a sensible dependence on the RAFT agent. It is also found that R-M has a close relationship with the strength of the EAMF and the concentration of the RAFT agent. Detailed discussion reveals that R-M can be used as a characteristic parameter to measure the extent of cross-termination in RAFTP. The experimental technique offers an efficient way to quantitatively probe the cross-termination in situ, and sheds light on the mechanism of RAFTP.