Retardative chain transfer in free radical free-radical polymerisations ofvinyl 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 degreesC u nder a variety of conditions were investigated. The bulk reaction was succe ssfully modelled using conventional free-radical polymerisation with termin ation rate coefficients calculated from diffusion theory. The reaction was strongly retarded by the presence of toluene or low-molecular-weight polyis oprene. This retardation behaviour was consistent with a mechanism comprisi ng chain transfer of the radical activity to a double bond on the polyisopr ene backbone to form a radical centre of low reactivity, which may subseque ntly terminate with other propagating radicals ("transfer-induced retardati on"). 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 fr om the propagating VneoD radical to toluene and to polyisoprene. The rate c oefficients for transfer to toluene determined by both methods were similar (7.5 dm(3) mol(-1) s(-1) from the conversion-time data, and 10.8 dm(3) mol (-1) s(-1) from the molecular weight distribution). The rate coefficient fo r transfer to toluene was similar for both vinyl acetate (9.9 dm(3) mol(-1) s(-1)) and VneoD, as expected given the similar radical reactivity of thes e monomers. The rate coefficient for transfer to polyisoprene was found by the conversion-time method to be 150 dm(3) mol(-1) s(-1), suggesting that t he polymerisation of VneoD in the presence of polyisoprene would be a usefu l method for inducing grafts onto the polyisoprene backbone. The rate coeff icients and inferred mechanism are similar to those found previously for a VneoD/polybutadiene system [Macromolecules, 33 (2000) 2383]. (C) 2000 Elsev ier Science Ltd. All rights reserved.