Theoretical Validation of Single-Pulse Pulsed-Laser Polymerization as a Method for Investigating Chain-Length-Dependent Termination

Abstract

Abstract Ideally, single-pulse pulsed-laser polymerization (SP PLP) experiments are marked by a simple relation between time and radical chain length. Thus time-resolved data from such experiments have the potential to directly reflect the chain-length dependence of the termination reaction. However this capability is hostage to various assumptions. These are investigated by performing a series of theory vs. theory comparisons. On the one hand, assumption-free simulations of the kinetics of SP PLP experiments are carried out. The results thus generated are compared with the predictions of equations derived by making assumptions. In this way it is possible to gauge the rectitude of data-analysis methods based on the equations. In turn, the following assumptions are investigated: (1) That of radicals being of length 0 at time 0; (2) That of all radicals terminating at the same rate at any instant; (3) That of transfer being negligible; (4) That of termination being described by a simple power-law; and (5) That of propagation being chain-length independent in rate. All these assumptions are probed in relation to analysis of SP PLP kinetic data, while assumptions (1) and (4) are looked at in relation to the analysis of molecular weight distributions. While some surprising findings do emerge, for the most part it is found that data-analysis methods are reasonably robust, even if they will generally result in underestimation of the true strength of the chain-length dependence of termination. Further, it is possible to make these methods even more accurate by adopting some refinements that are recommended. In general the outstanding potential of SP PLP experiments for investigating the chain-length dependence of the termination reaction is validated.