(The) particle size and molecular weight distributions in suspension polymerization of styrene

Abstract

The suspension polymerization of styrene using benzoyl peroxide (BPO) as initiator and poly(vinyl alcohol) as suspension stabilizer was carried out in a four-neck flask at 80,85, and 90 ℃. The sizes of polystyrene particles were determined by screen analysis using standard testing sieves and the molecular weights were obtained by measuring the intrinsic viscosity and analyzing the Gel Permeation Chromatograms. The particle sizes produced in this study ranged between 0.03 and 0.4cm. The average bead diameter decreased with PVA concentration and water to monomer phase ratio, and increased with BPO concentration. The average molecular weight decreased slightly with particle size in the same sample, showing the existence of masstransfer intrusion. The dispersity ratio ($\overline{M}_w/\overline{M}_N$) varied from 1.6 to 2.3. The molecular weight distribution curves have nearly the same shape except for a slight difference in the position of peak occurrence in the chromatograms of the polystyrene particles of different sizes. By measuring the weight of polymer formed and calculating the conversion rate of styrene monomer into polystyrene, the overall activation energy of 21,600 cal/gmole was obtained.