Computer simulation of successively solutional fractionation of macromolecules

Abstract

Abstract The successive solution fractionation (SSF) ( i.e. , the successive solvent extraction of coacervate) was simulated by using an electronic computer. A polymer having the most probable distribution of number average degree of polymerization, X 0 n = 150, and weight average degree of polymerization, X 0 w = 300, was hypothetically fractionated, on the basis of the generalized FLORY‐HUGGINS‐FUJISHIRO theory in which the concentration dependence of the polymer/solvent interaction parameter, expressed as p, was taken into account. As p is increased the composition of the fraction with a larger degree of polymerization (X), obtained by SSF, decreased, while the smaller X region remained almost constant. The composition of the fraction in the region of the smaller X is much smaller than that obtained from successive precipitation fractionation (SPF). The fractionation data ( X w and the amount of the fraction) were analyzed according to the treatment of SCHULZ and of KAMIDE et al . The results revealed that the first one is preferable to the second one in the case of SSF. The broadness of the molecular weight distribution in the fraction markedly decreased with decrease in the initial concentration of polymer, v 0 p , if v 0 p was higher than 0.1%. An asymtotic, limiting value for X w / X n of an extremely small fraction of polymer, separated by SSF, was appreciably larger than that from SPF, but the corresponding value for the standard deviation was zero. The molecular weight distribution of the fractions becomes narrower as their amount is smaller. This behaviour is in contrast to the case of SPF. In SSF, a decreasing in the relative amount of each fraction, besides that of an initial concentration, effectively enables fractions of narrow distribution to be obtained.