Retardative chain transfer in free radical free-radical polymerisations of vinyl neo-decanoate in low molecular weight polyisoprene and toluene

The kinetics of free-radical polymerisation of vinyl neo-decanoate (VneoD) and the molecular weight distributions (MWDs) of the polymers formed in the presence and absence of low molecular weight polyisoprene at 50°C under a variety of conditions were investigated. The bulk reaction was successfully modelled using conventional free-radical polymerisation with termination rate coefficients calculated from diffusion theory. The reaction was strongly retarded by the presence of toluene or low-molecular-weight polyisoprene. This retardation behaviour was consistent with a mechanism comprising chain transfer of the radical activity to a double bond on the polyisoprene backbone to form a radical centre of low reactivity, which may subsequently terminate with other propagating radicals (“transfer-induced retardation”). Analysis of the rate and of the MWDs of the polymer formed yielded an estimation of the rate coefficient for transfer of the radical activity from the propagating VneoD radical to toluene and to polyisoprene. The rate coefficients for transfer to toluene determined by both methods were similar (7.5 dm3 mol−1 s−1 from the conversion-time data, and 10.8 dm3 mol−1 s−1 from the molecular weight distribution). The rate coefficient for transfer to toluene was similar for both vinyl acetate (9.9 dm3 mol−1 s−1) and VneoD, as expected given the similar radical reactivity of these monomers. The rate coefficient for transfer to polyisoprene was found by the conversion-time method to be 150 dm3 mol−1 s−1, suggesting that the polymerisation of VneoD in the presence of polyisoprene would be a useful method for inducing grafts onto the polyisoprene backbone. The rate coefficients and inferred mechanism are similar to those found previously for a VneoD/polybutadiene system [Macromolecules, 33 (2000) 2383].