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

✍ Scribed by Michael Buback; Markus Busch; Ralf A. Lämmel

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 948 KB
• Volume: 5
• Category: Article
• ISSN: 1022-1344
• DOI: 10.1002/mats.1996.040050505

✦ Synopsis

Abstract

The 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 k~p~. 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~p~ 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 simulatioenous high quality of the SEC (low broadening) is very well suited for the k~p~ 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.