Requirements associated with studies into a chain-length dependence of propagation rate coefficients via PLP-SEC experiments

Experiments directed toward the determination of free-radical propagation rate coefficients kappa(p) from pulsed laser initiated polymerizations (PLP) in conjunction with size-exclusion chromatography (SEC) were modeled using the program PREDICI. The simulations were carried out in order to investigate whether an experimentally observed variation of kappa(p) with the initiating laser pulse repetition rate is necessarily due to a chain-length dependence of kappa(p) The modeling was performed for laser pulse repetition rates ranging from 0.5 to 50 Hz and primary radical concentrations being varied by more than 2 orders of magnitude. The resulting molecular weight distributions were very different in shape. The kappa(p) data derived from the simulated molecular weight distributions showed a variation of about 30% with chain lengths, although the same propagation rate coefficient was introduced into all the simulations. The experimental finding of kappa(p) being dependent on chain length induced by using different laser pulse repetition rates is not necessarily due to a chain-length dependence of kappa(p). The modeling results show the importance of reporting all experimental details together with kappa(p) data derived from PLP-SEC experiments.