When a polymerizable system is subjected to periodic light flashes, which induce the formation of primary radicals, a pseudostationary state is established which is characterized by a periodic profile of the (polymer) radical concentration. Within such a period of length 6 the radical concentration will decay according to a second-order rate law. At the end of this period the radicals, which have escaped termination up to this moment, have propagated up to a chain length L, = 6 . $ . cM , $ representing the propagation rate constant and c, the monomer amount concentration. When the next flash arrives these radicals are opposed to a strongly increased overall concentration of radicals which leads to an enhanced probability for their termination. As a consequence the formation of dead polymer molecules with a chain length close to L, is favoured. The chain-length distribution of polystyrene prepared under such pseudostationary conditions, which was evaluated by gel permeation chromatography, in fact exhibits such a peak. The analysis of the theoretical distribution curves, derived in this communication, reveals that it is easily possible to correlate this peak to L, , independently of the mode of termination (disproportionation or combination). Thus, a method of evaluating / ci , is derived without any reference to the termination rate constant 4 and largely independent of all features which usually cause problems in the evaluation of kp and 4 (such as primary radical termination etc.). The experimental results agree fairly well with the data reported in literature, especially with those obtained from the number of particles and the rate of polymerization in emulsion systems.

A newly developed method for the determination of the radical reactivity ratios is presented. Two main equations are used and the parameters can be calculated from the ordinate and the slope of the linearization plots. Both equations yield identical values when applied to synthetic data which conforms to the ideal situation of no error in the input data. As experimental data are always subject to some kind of error, a sensitivity analysis was carried out which took into account a relatively pronounced error in the monomer reactivity ratios. It turned out that the new linearization method may even be indicative of the quality of the input data under favorable conditions.magnified image

A large number of the already published data of the experimental rate constants of propagation as a function of the monomer composition for copolymerization systems has been analyzed by applying a linearization procedure (introduced in the preceding publication) and new linear least square methods in order to obtain the radical reactivity ratios s. The compilation of data comprises the originally published parameter sets and those determined by the alternative methods. Besides the determination of the s parameters, the linearization plots also offer the possibility to rate the error of data sets as either non‐correlated or systematic. Simulations taking into account a random scatter in the experimental values give more insight into the accuracy of data. The limited applicability of the simplifying assumptions introduced by Fukuda et al. is confirmed. Correlations between the monomer and radical reactivity ratios, respectively, and the homopropagation rate constants are investigated. A systematic procedure for rating radical reactivity ratios based on the linearization procedure is proposed.