INVESTIGATION OF METHACRYLATE FREE-RADICAL DEPROPAGATION KINETICS BY PULSED-LASER POLYMERIZATION

An extensive study of free-radical depropagation kinetics has been per formed for several methacrylates at high temperatures in bulk and solu tion using a pulsed-laser technique. As expected from theory, the rela tive importance of depropagation on rate increases with increasing tem perature and with decreasing monomer concentration. The temperature de pendence 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 b est-fit values (-53.8 kJ/mol and -113 J/(mol.K)) provide a good repres entation of high-temperature propagation/depropagation kinetics measur ed for n-butyl, cyclohexyl, isobornyl, and 2-hydroxypropyl methacrylat es, suggesting that a single set of universal values may be employed w hen modeling high-temperature polymerizations of all methacrylates.