Detailed analysis of radical polymerisation kinetics by pulsed-laser techniques*

Abstract

Pulsed-laser-assisted methods have enormously improved the understanding of kinetics and mechanism of the basic steps of radical polymerisation, i.e. of initiation, propagation, and termination. The decarboxylation kinetics of primary radicals from peroxyester dissociation was studied on a picosecond time scale by UV-pump – VIS/NIR/IR probe experiments. The application of sequences of laser pulses and the subsequent analysis of the structure on the molar mass distribution of so-obtained polymer allows for the reliable measurement of propagation rate coefficients as a function of temperature, pressure and solvent environment. The SP–PLP–EPR technique has emerged as the leading method for addressing the complexity of radical termination. Unrivalled insight into the kinetics is provided by the highly time-resolved measurement of reacting species, i.e. of radicals at sub-micromolar concentrations via electron paramagnetic resonance spectroscopy. The impact of chain length on termination rate may be accurately determined within a wide range of monomer conversion and, via characteristic EPR bands, even for several radical species, which occur whenever backbiting takes place. Application of laser-assisted techniques extends chemical kinetics to very large species and to reactions under heavy diffusion control. The novel techniques demonstrate that polymerisation kinetics obeys the fundamental principles established for small species.