Termination, Propagation, and Transfer Kinetics of Midchain Radicals in Methyl Acrylate and Dodecyl Acrylate Homopolymerization

Methyl acrylate (MA) and dodecyl acrylate (DA) homopolymerizations (1.5 M in toluene) were investigated via single pulse-pulsed laser polymerization in conjunction with detection of the type and of the concentration of radicals by electron paramagnetic resonance spectroscopy (SP-PLP-EPR). The evolution of secondary propagating (SPR) and midchain (MCR) radicals, after instantaneous laser-induced production of an intense burst of primary radicals, was measured with a time resolution of microseconds from 0 to 60 degrees C. With the kinetics of chain-length-dependent termination and of propagation for SPRs being already known from experiments at subzero temperature, the rate coefficients for the formation of MCRs from SPRs by backbiting, k(bb), of propagation from MCRs, k(p)(t), and of cross-termination between an SPR and an MCR, K-t(st), were deduced. The present paper aims at elucidating the impact of the size of the ester side chain on k(bb), k(p)(t), and k(t)(st). In passing from MA to DA (in 1.5 M solution of toluene), the rate coefficients are lowered by factors of about 1.5 for k(bb), 3.7 for k(p)(t), and 8 for k(t)(st), depending on polymerization temperature. Together with the earlier results for SPRs, the reported data provide a comprehensive set of rate coefficients for the simulation of MA and DA homopolymerizations in solution. The data may be used for estimating, by interpolation, the rate coefficients of acrylates with intermediate sizes of the alkyl side chain.