Investigation of methacrylate free-radical depropagation kinetics by pulsed-laser polymerization

An extensive study of free-radical depropagation kinetics has been performed for several methacrylates at high temperatures in bulk and solution using a pulsed-laser technique. As expected from theory, the relative importance of depropagation on rate increases with increasing temperature and with decreasing monomer concentration. The temperature dependence of n-dodecyl methacrylate depropagation has been quantified. The resulting estimates for enthalpy (-50 to -60 kJ/mol) and entropy (-105 to -127 J/(mol.K)) of polymerization, although highly correlated, are in good agreement with available literature data. Moreover, the best-fit values (-53.8 kJ/mol and -113 J/(mol.K)) provide a good representation of high-temperature propagation/depropagation kinetics measured for n-butyl, cyclohexyl, isobornyl, and 2-hydroxypropyl methacrylates, suggesting that a single set of universal values may be employed when modeling high-temperature polymerizations of all methacrylates.