Propagation kinetics of isoprene radical homopolymerization derived from pulsed laser initiated polymerizations
The propagation kinetics of isoprene radical polymerizations in bulk and in solution are investigated via pulsed laser initiated polymerizations and subsequent polymer analyses via size-exclusion chromatography, the PLP-SEC method. Because of low polymerization rate and high volatility of isoprene, the polymerizations are carried out at elevated pressure ranging from 134 to 1320 bar. The temperatures are varied between 55 and 105 °C. PLP-SEC yields activation parameters of kp (Arrhenius parameters and activation volume) over a wide temperature and pressure range that allow for the calculation of kp at technically relevant ambient pressure conditions. The kp values determined are very low, e.g., 99 L mol−1 s−1 at 50 °C, which is even lower than the corresponding value for styrene polymerizations. The presence of a polar solvent results in a slight increase of kp compared to the bulk system. The kp values reported are important for determining rate coefficients of other elemental reactions from coupled parameters as well as for modeling isoprene free-radical polymerizations and reversible deactivation radical polymerization with respect to tailored polymer properties and optimizing the polymerization processes.