The determination of chain-length dependent rate coefficients in free radical polymerization by pseudostationary techniques

lt is the aim of the project to determine the rate constants of termination kt in free radical polymerization by means of new approaches. This is not trivial because kt is chain-length dependent, obeying a power-law of the type kt=k t0 . P-b (P=chain-length). This necessitates the evaluation of two parameters in each case. The methods proposed are based on a direct determination of the rate constant of chain propagation kp by means of laser-pulsed initiation and subsequent analysis of the chain-length distribution (cld) and either an evaluation of the second moment of the cld or a measurement of the rate of polymerization. In both cases estimated averages are obtained for kt which are in good agreement with the true average. These averages are plotted vs. the number average degree of polymerization on a double logarithmic scale for the determination of kt0 . and b. The quantity b should be further controlled by a curve-fitting procedure of the cld obtained for experiments with low pulse frequencies. In this way, the sparse knowledge of reliable termination constants should be improved and the kt-function determined for various bulk, solution, and copolymerization systems. Furthermore, the value of the exponent b should convey valuable information on the mechanism of termination.