Studies on the propagation reaction in the free radical polymerization of ethyl alpha-hydroxymethacrylate

The free radical propagation kinetics of ethyl alpha -hydroxymethacrylate h ave been investigated using pulsed-laser polymerization experiments. Experi mental conditions were not optimised for successful experiments in bulk mon omer, where transfer caused complications in the interpretation of the data . However, in solutio and at low temperatures (below 45 degreesC), successf ul experimental conditions were identified and an extensive data set of pro pagation rate constants is reported. A remarkable dependence of the propaga tion rate coefficient k(p), on the solvent was observed. The variation in k (p) is exemplified by the range obtained at 15 degreesC where k(p) was foun d to fall between 580 (THF) and 1860 (xylene) L/mol/s. The Arrhenius parame ters for the propagation reaction were obtained in three solvents (tetrahyd rofuran, toluene and ethanol) at three different dilutions. The samples wit h the highest concentration of EHMA yielded values for the activation energ y of 15-16 kJ/mol and pre-exponential factors 5-10 times lower than those p reviously reported for ethyl methacrylate. Both Arrhenius parameters were s trongly dependent on solvent type and concentration. A hypothesis for these results is tendered - suggesting direct interaction sin the transition sta te between the monomer and the propagating radical. These specific interact ions are ameliorated to a greater or lesser extent by the inclusion of diff erent solvents.