Synthesis and characterization of polystyrene-b-polyisoprene-b-poly(methylmethacrylate) triblock copolymer

Polystyrene-b-polyisoprene-b-poly(methylmethacrylate) (PS-b-PI-b-PMMA) triblock copolymer was synthesized by sequential anionic polymerization. The as-synthesized triblock copolymer contains side products of inadvertently terminated PS and PS-b-PI precursors. The side products can be effectively removed by semi-prep scale liquid chromatography using multiple injection method to obtain pure PS-b-PI-b-PMMA. It was found that the removed side product contains another polymer species, coupled PS-b-PI, which could not be recognized by size exclusion chromatography (SEC) analysis since the elution peak of the coupled product overlaps with that of PS-b-PI-b-PMMA. This study demonstrates that the size based separation of SEC is often not good enough to characterize complex polymers precisely and interaction chromatography can render unique advantage over SEC analysis.