Phase separation of binary copolymers from solution non-solvent mixtures in relation to copolymer structure, and polymer-solvent interactions

Abstract

Turbidimetric titration is well established as a technique for determining the nature and composition of a polymer in dilute solution by its precipitation behaviour on titration with non-solvent. Although the technique is simple, there are many experimental and theoretical difficulties in obtaining reliable results. Here, a novel technique is described which overcomes some of the experimental difficulties of the titration technique. In particular, the polymer concentration remains constant. Results presented illustrate how clearly pure graft and block copolymers may be distinguished by this technique from constituent homopolymers, their physical mixtures or the corresponding random copolymers of similar molecular weight. The turbidity-precipitant content graphs are sigmoidal in form, but pure graft or block copolymers show a distinct double inflection in the middle of the graph. The effects appear in several different polymer solution systems studied and may be quite general.