Preparative fractionation of a random copolymer (SAN) with respect to either chain length or chemical composition

TL;DR

This paper investigates methods to fractionate random copolymers of styrene and acrylonitrile (SAN) by chain length or chemical composition using liquid/liquid phase equilibria, revealing conditions favoring each separation type.

Contribution

It demonstrates how phase separation mechanisms can be controlled to selectively fractionate SAN copolymers by chain length or composition, depending on the system setup.

Findings

Fractionation by chain length occurs in SAN/toluene solutions.

Composition-based fractionation is possible with SAN and polystyrene in dimethyl acetamide.

Different phase separation mechanisms are explained theoretically.

Abstract

The possibilities to fractionate copolymers with respect to their chemical composition on a preparative scale by means of the establishment of liquid/liquid phase equilibria were studied for random copolymers of styrene and acrylonitrile (san). Experiments with solutions of san in toluene have shown that fractionation does in this quasi-binary system, where demixing results from marginal solvent quality, take place with respect to the chain length of the polymer only. On the other hand, if phase separation is induced by a second, chemically different polymer one can find conditions under which fractionation with respect to composition becomes dominant. This opportunity is documented for the quasi-ternary system dmac/san/polystyrene, where the solvent dimethyl acetamide is completely miscible with both polymers. The theoretical reasons for the different fractionation mechanisms are discussed.