Determination of free-radical propagation rate coefficients for alkyl methacrylates by pulsed-laser polymerization

Values of free-radical propagation rate coefficients (k(p)) for two new methacrylate monomers-2-ethylhexyl and isodecyl methacrylates-have been measured in the temperature range 10-90 degrees C by analyzing molecular weight distributions of polymer produced by pulsed-laser polymerization (the PLP/MWD technique). In addition, new PLP/MWD results for n-butyl and n-dodecyl methacrylates are reported, and previously published data for ethyl and isobutyl methacrylates are reanalyzed. The temperature dependence of k(p) for these six monomers is compared to that recently reported for methyl methacrylate. A consistent increase of k(p) with size of the ester group is observed, with values for n-dodecyl methacrylate 50-60% higher than those for methyl methacrylate. Although this increase is statistically significant, it is less certain whether it is attributable to a decrease in the activation energy or an increase in the frequency factor. The experimental results favor the former explanation.