The effect of intramolecular transfer to polymer on stationary free radical polymerization of alkyl acrylates

New expressions that account for the formation of acrylate midchain radicals by intramolecular transfer and their subsequent propagation, termination, and transfer events have been derived for polymerization rate, average chain-length, and chain-length distribution under stationary conditions. The nonidealities observed in previous kinetic studies are captured in a single lumped rate coefficient, theta, that controls the apparent order of rate on monomer concentration. Applied to rate data from the literature, the treatment yields consistent estimates for theta and k(p)/k(t)(0.5) for butyl acrylate polymerization at 50 degreesC. Combining these ratios with chain-end propagation values determined by pulsed-laser polymerization, intramolecular transfer rate coefficients estimated from C-13 NMR data, and/or radical concentrations measured by ESR provides a new means to estimate the individual rate coefficients for acrylate polymerization systems. It is also shown that estimates for butyl acrylate transfer to monomer rate coefficients obtained from chain-length distributions are valid even in the presence of acrylate backbiting events.