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 °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.