Abstract
A sample of polymethyl methacrylate obtained by bulk polymerization was fractionated by Baker and Williams type column fractionation method and the experimental conditions and the results of the fractionation were discussed. Methyl ethyl ketone (MEK)-ethanol (EtOH) mixture (MEK: EtOH= 6: 4) was used as the solvent. EtOH as the precipitant, and glass beads (50-140 mesh or 100-200 mesh) as the supports and the flow rate of the solvent was maintained at about 40 mi/hr. With the sample weight of O.5g, it was found that better results were obtained when thermal gradient was set on the column than when there was no thermal gradient, and also when the sample was deposited on the beads by selective method than when deposited by non-selective method.
Fractionation data were treated by Tung's method to determine molecular weight distribution for the unfractionated sample and to calculate the weight-average and number average molecular weights (Mw and Mn). The determined distribution did not agres very well with those determined by sedimentation velocity (SV) and by gel permeation chromatography (GPC). The value of Mw/Mn, calculated from the fractionation data agreed well with that obtained from the SV data and the observed value (Mw determined by light scattering and Mn determined by osmotic pressure), but did not agree well with that obtained from the GPC data.
