Effect of Block Composition and Molecular Weight in the Structure of Toroidal Micelles

Abstract

Block copolymers self-assemble into a micelle in a selective solvent. Recently, Huang et al. reported the highly uniform donut-shaped micelle from polyisoprene-block-poly(2-vinylpyridine) (PI-b-P2VP) in mixture solvent system. In this study, we have investigated factors such as block composition and total molecular weight of PI-b-P2VP in the structural behavior of donut-shaped micelle.Two series of PI-b-P2VP samples were synthesized by anionic polymerization. The first series of PI-b-P2VPs have the same total molecular weight with various block composition. Second series exhibits the same block composition with various total molecular weight. PI-b-P2VPs were fractionated by temperature gradient interaction chromatography in order to get rid of by-product in the sample. The prepared micelle was characterized by dynamic and static light scattering in solution state, and their structures were visualized by atomic force microscopy.Generally, morphological changes of micelle are induced by different block compositions of diblock copolymer. However, donut-shaped micelle was shown in wide range of PI block composition from 0.5 to 0.8. Those micelles have similar hydrodynamic radius, however, as volume fraction of core block decreases, aggregation number are getting smaller. And the hydrodynamic size of donut-shaped micelle depends on the total molecular weight.