SP-PLP-EPR - A Novel Method for Detailed Studies into the Termination Kinetics of Radical Polymerization

Single pulse pulsed laser polymerization electron paramagnetic resonance (SP-PLP-EPR) has been introduced as a powerful method for the very detailed analysis of termination kinetics. During polymerization an intense laser pulse is applied in order to almost instantaneously produce a burst of radicals. The decay of radical concentration is measured by highly time-resolved EPR and is analyzed with respect to the rate coefficients for the termination of two radicals of identical size. SP-PLP-EPR experiments have been carried out for an itaconate monomer, for several methacrylates in bulk and in a solution of ionic liquids, for methacrylic acid in aqueous solution, and for the solution polymerization of butyl acrylate in toluene at low temperature. The data fully support the composite model, which assumes a stronger chain-length dependence of termination for radicals of smaller size and a weaker one for large radicals. The SP-PLP-EPR technique is also applicable in systems with more than one type of growing radicals, as is the case with butyl acrylate polymerization at higher temperature and with RAFT polymerizations, where the novel method may be used for a comprehensive kinetic analysis.