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SUMMARYThe use of pulsed lasers to induce radical polymerization with a subsequent analysis of the polymer molecular weight distribution (MWD) through size exclusion chromatography (PLP-SEC method) revolutionized the determination of propagation rate coefficients kv In this paper the program package PREDICI is applied to the simulation of PLP-SEC orginated MWDs. The comparison with SPEEDUP-simulations from Hutchinson et al. shows that both programs are equally well suited for the calculation of the MWD of PLP samples. The emphasis is on the study of the effects that the experimental parameters, i.e. the primary radical concentration in a specific experiment, the gradients of this radical concentration, and above all the instrumental broadening of SEC analysis, have on the measured MWD, and therewith on the k, determination via PLP experiments. By detailed consideration of a styrene bulk polymerization experiment at 70 "C and ambient pressure, it is shown that the PLP-SEC technique at primary radical concentrations between those given by the limiting cases of the low and high termination rate limits and with simultaneous high quality of the SEC (low broadening) is very well suited for the kp determination, As the MWD of samples from PLP is influenced in a rather complex fashion by the kinetics of the polymerizing system, by the choice of the experimental parameters determining laser-induced primary free radical concentration, and by the performance of the SEC device, it appears highly recommendable to accompany PLP studies by simulation.

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There is currently a highly controversial debate about the nature of the reversible addition-fragmentation chain transfer (RAFT) mechanism. In this debate, kinetic computer modeling is frequently used as a powerful tool to correlate experimental data with theoretical models to deduce the rate coefficients that govern the process. Frequently, the PREDICI program package has been used as a simulation tool. Recently, the implementation and mathematical basis of the RAFT process, with respect to PREDICI, have been criticized. This communication discusses the mathematical and mechanistic implementation of the RAFT process in the PREDICI program package and elucidates the well-founded mathematical basis of the approach.

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