Preparation of monodisperse polymer samples by solubility difference method

An attempt was made to prepare the polymer fractions having extremely sharp molecular weight distribution (MWD), by using a successive solutional fractionation (SSF) method, in which a polymer-lean phase was separated as a fraction from a polymer-rich phase. For this purpose a large-scale preparative SSF apparatus was constructed. Atactic polystyrene (PS) high-density polyethylene (PE), and cellulose di- and tri-acetates (CDA and CTA) were fractionated by SSF. The fractions isolated from a quasi-binary mixture (polymer/solvent system) have the same MWD as that predicted by the computer simulation technique. Even under the conventional fractionation conditions (initial polymer volume fraction vop = ∼ 0.01, total number of fractions nt = 10 ∼ 20) the fractions with the ratio of the weight to number-average molecular weight Mw/Mn less than 1.1 for PS, 1.2 for PE, 1.3 for CDA and 1.4 for CTA were obtained, with exception of a few initial fractions. The advantage of the SSF method was clarified over the conventional preparative methods such as gel permeation chromatography and the column fractionation method.