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 k p. 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 L 0 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 k p 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.

Investigation of the Chain Length Dependence of kp: New Results Obtained with Homogeneous and Heterogeneous Polymerization

“…Thus the chain length dependence of the k p values can not only be compared directly for the two polymerization systems but can also be compared with the data published by Willemse et al [2] The filled diamonds (triangles) represent the results for the polymerization in microemulsion (solution) as deduced from the location of the point of inflection on the low molecular weight side; the full squares (inverted triangles) represent the data obtained from the peak maximum. All four data sets show the same general trend of a chain length dependence persisting to higher chain lengths as was already shown by Olaj et al [1,24] In order to make sure that BB can be excluded as a possible source for discre- The corresponding open symbols represent the results after application of the correction (Equations (7a) and (7b)). The CLD function calculated according to Equation (8) is included as full and broken curve, respectively, which are only shifted by the constant value as indicated.…”

Solvent Influence on Propagation Kinetics in Radical Polymerizations Studied by Pulsed Laser Initiated Polymerizations

“…[15,16] More recently, SEC broadening and its influence on k p determination was addressed by van Herk, [75][76][77] as well as by Olaj and Schnöll-Bitai. [78][79][80][81][82] In PLP experiments, an evenly spaced sequence of laser pulses, mostly at a UV wavelength, is applied to the reaction system containing monomer and a photoinitiator. As discussed by García and coworkers, in particular at high laser pulse repetition rates and/or high energy per laser pulse, special care has to be taken to avoid a temperature increase during pulsing.…”

Ab Initio Study of Free‐Radical Polymerization: Polyethylene Propagation Kinetics

“…[4] A recent re-evaluation of the experimental data of reference [3] by Olaj et al confirmed their former conclusion that the long-range chain-length dependence of k p extends over several hundreds of propagation steps. [5] Olaj et al explicitly reject the alternative view of Willemse et al that only the k p data for extremely short chains are responsible for this chain-length dependence.…”