Precipitation fractionation of block copolymers

Abstract

Possibilities offered by classical precipitation fractionation in the preparative separation of polymer admixtures from block copolymers and in an estimate of the polydispersity in molar mass and of the heterogeneity in chemical composition of block copolymers have been examined. A mixture of a two-block copolymer, polystyrene-block-polyisoprene, with polystyrene was separated in the systems cyclohexane/1-propanol and 1,4-dioxan/1-propanol, and a mixture of three two-block styrene-isoprene copolymers having different chemical composition was fractionated in the system benzene/methanol. In the cyclohexane/1-propanol system, two commercial samples of three-block copolymers polystyrene-block-poly(ethene-co-butene)-block-polystyrene and their mixture were fractionated. The results showed that the polydispersity and chemical heterogeneity thus estimated are much lower than the real ones, especially due to the colloid properties of block copolymers.