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.