Continuous spin fractionation and characterization by size-exclusion chromatography for styrene-butadiene block copolymers

Linear and star-shaped styrene-butadiene block copolymers synthesized by anionic polymerization of butadiene and styrene were fractionated by applying a newly developed large-scale fractionation technique, named continuous spin fractionation (CSF). Their molecular weight and polydispersity index (d = Mw/Mn) were measured with size-exclusion chromatography and static light scattering. For the linear triblock copolymer a fractionation via temperature variation turned out to be better suited than the usual isothermal procedure. The star-shaped polymer with the d value of 1.33 was fractionated in two CSF steps to get the targeted sample, which has a considerably more uniform structure and a narrower molecular weight distribution (d = 1.11). The corresponding starting linear diblock copolymer was fractionated in one step reducing d from 1.68 to 1.17. With one set of simple laboratory equipment, 1 kg polymer can be fractionated per day. Utilizing CSF, for the first time, we fractionated successfully the block copolymers.