Continuous fractionation and solution properties of PVC, 1. Continuous fractionation, characterisation

Abstract

AbstractA new Continuous Polymer Fractionation method, called CPF, is described. The polymer to be fractionated is dissolved in a solvent/non‐solvent mixture, and this solution (feed) is extracted continuously by a second liquid (extracting agent), which contains the same solvent components as the feed. In the case of PVC, the fractionation was carried out with a pulsed counter current extraction apparatus and THF/water was used as solvent/non‐solvent mixture. Fractionation is achieved by the fact that the molecules are distributed over the counter current phases according to their chain length; the feed leaves the column as gel and the extracting agent as sol. First some explorative experiments were made in order to determine suitable working parameters, like frequency and amplitude of pulsation, compositions of feed and extracting agent and the ratio of flow. With the so obtained parameters, preparative experiments were carried out, yielding five PVC‐fractions with molecular weights ranging from 20 000 to 100 000 (GPC, LS) and non‐uniformities, U = (Mw/Mn) −1, of about 0,2 (GPC) using a starting material with Mw = 67 000 and U = 0,95.