Chain Length Dependence of Chain Propagation Revisited

Abstract

On the basis of recently developed numeric procedures, the results obtained for the propagation constants kp by means of the PLP−SEC method (pulsed laser polymerization followed by size exclusion chromatographical analysis of the chain length distribution) were subjected to a critical reevaluation and reanalysis particularly with respect to the chain length dependence of kp. In this context the errors arising from a broadening caused by axial dispersion in the SEC were largely eliminated together with other uncertainties in assessing the characteristic chain length L0 on which the evaluation of kp is based. The main result that refers to the bulk polymerization of methyl methacrylate and styrene in the temperature range 25−70 °C is that the previously found negative long-range chain length dependence of kp survived this procedure to an extent that widely exceeds the known variation of kp for extremely short chains and extends over a range of several hundreds of propagation steps.