Effect of average molecular weight of the original polymer on the separation characteristics in successive solutional fractionation

Abstract

AbstractWhen solutions of a polymer with a molecular weight distribution (MWD) having a great variety of the average molecular weights are solutionally fractionated, the effect of the average molecular weight on the phase separation features can be described by means of a hypothetical calculation technique. The Flory‐Huggins theory is employed as a basic principle for the simulation. The partition coefficient, σ, as well as the volume ratio of the polymer‐lean phase to the polymer‐rich phase, R, decrease with an increase in the average molecular weight of the original polymer under the same operating conditions, i.e., initial concentration, v, the concentration dependence of the polymer/solvent interaction parameter, p, and the amount of fraction, ϱ. The value of standard deviation, σ′, of MWD in the fraction is predominantly influenced by σ, irrespective of the average molecular weight and of MWD type in the original polymer.The fractions obtained by successive solutional fractionation (SSF) are approximately symmetric with respect to the peak and their MWD in the fractions, obtained under the same operating conditions, become broader with increasing weight‐average degree of polymerization X̄ of the original polymer. Very sharp fractions can be separated by SSF even if X̄ is varied over a tenfold range. The superiority of SSF over successive precipitational fractionation (SPF) is very apparent for large X̄ polymers.