The mechanism and thermodynamic studies of CMRP: Different control mechanisms demonstrated by CoII(TMP), CoII(salen?), and CoII(acac)2 mediated polymerization, and the correlation of reduction potential, equilibrium constant, and control mechanism

The mechanism study of cobalt mediated radical polymerization (CMRP) is performed with CoII(TMP), CoII(salen?), and CoII(acac)2 at 60 C to demonstrate that the control of vinyl acetate radical polymerization is achieved via a degenerative transfer pathway when CoII(TMP) and CoII(salen?) are used but via a reversible termination process with equilibrium constant (Keq) equal to 1.4 ? 106 m-1 when CoII(acac)2 is the mediator. Given by the measured Keq in CMRP with varied cobalt complexes and the reduction potential (E1/2) of the corresponding cobalt complexes, a linear correlation between log(Keq), and E1/2 is found and can be used to estimate the Keq of other CMRP systems. With the enriched database of Keq values, the control mechanisms of CMRP are quantitatively defined by CoII/CoIII equilibrium constant. The connection of reduction potential, equilibrium constant, and control mechanism would contribute to the in-depth understanding of CMRP process. The control mechanisms in cobalt mediated radical polymerization (CMRP) are quantitatively defined by the CoII/CoIII equilibrium constants, which are either measured by following the cobalt concentration or derived from the reduction potentials of corresponding cobalt species using the linear correlation of log(Keq) and E1/2. The difference of control mechanisms in CMRP is demonstrated by vinyl acetate polymerization mediated by varied cobalt complexes as well. ? 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.