Supramolecular self-assembly of an ABA-Triblock bottlebrush polymer: Atomic-force microscopy visualization of discrete oligomers

A novel ABA-triblock bottlebrush polymer (PS-PD-PS), whose terminal PS block and central PD block were densely grafted with polystyrene and poly[2-(dimethylamino)ethyl methacrylate], respectively, on polynorbornene backbones was synthesized by three mutually orthogonal types of controlled polymerization. Dynamic light-scattering analysis revealed that in polar solvents such as tetrahydrofuran/water (99:1, v/v), PS-PD-PS self-assembled into oligomeric-to-polymeric aggregates through solvophobic interaction of the PS block. The size of these aggregates depended on the concentration of PS-PD-PS and on the polarity of the solvent. Atomic-force microscopy (AFM), showed that single molecules of PS-PD-PS adopted a dumbbell shape in which the three blocks in PS-PD-PS could be clearly distinguished. In AFM samples prepared under appropriate conditions, PS-PD-PS self-assembled into discrete oligomeric aggregates with well-defined structure, including linear and cyclic dimers, a tadpole-like trimer, and higher oligomers. The arrangement and junctions of the monomeric units could be clearly visualized at a single-molecular level. [Display omitted] •Synthesis of an ABA-triblock bottlebrush polymer (PS-PD-PS) with adhesive PS-blocks.•Detailed DLS study on the self-assembling profiles of PS-PD-PS in the solution.•AFM visualization of monomeric PS-PD-PS with well-distinguishable three blocks.•AFM visualization of oligomeric aggregates of PS-PD-PS connected at the PS-blocks.•First observation of noncovalently ring-closed structures of bottlebrushes.