Modeling of molecular weight distribution in pulsed laser free‐radical homopolymerizations

Abstract

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.

Modeling of Emulsion Polymerization, Will It Ever be Possible ? Part‐2: Determination of Basic Kinetic Data Over the Last Ten Years

“…Also other authors used a constant broadening factor for correction of PLP data. [27,28] It has to be noted that the extend of column broadening depends on the quality of the SEC equipment and in particular the quality of the column or column set. The frequency dependence of k p was noted in many laboratories but the extend may differ because of the use of different columns.…”

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

“…[21] This is of a comparable dimension as the error introduced by (wrongly) using the location of the peak maximum in the low termination rate limit. [25] This leads to the question whether polymerization was really carried out in the high termination rate limit in all cases as was claimed by the authors. Usually, laser intensities decrease dramatically with increasing pulse separation times what would lead to the generation of lower concentrations of initiating radicals.…”

The Use of Simulation Techniques in Developing Kinetic Models for Polymerization

“…The benefits of accompanying experiments closely with modeling were demonstrated by Buback et al [8]. This is even the case for quite fundamental experiments such as the combination of pulsed laser polymerization experiments with subsequent analysis of polymeric product by size exclusion chromatography (PLP-SEC experiments), which is the IUPAC recommended master experiment for a model-free determination of propagation rate coefficients.…”