Shaping block copolymer micelles by supramolecular polymerization: making ‘tubisomes’

Abstract

Amphiphilic block copolymers in water usually self-assemble into spherical objects such as micelles or vesicles. Wormlike micelles are only formed in a small range of the block ratios. In all other cases an additional driving force is required to compel these materials into an anisotropic shape. To date crystallization processes have been the major force exploited to provide the necessary energy. Here, we demonstrate that supramolecular interactions can transform amorphous block copolymers which normally adopt a spherical configuration into a rigid cylindrical micelle called a tubisome. To create this force planar cyclic peptides (CP) are inserted at the interface between the hydrophilic and hydrophobic domains of amphiphilic block copolymers. The CPs form strong hydrogen bonds creating multiple stacks of the peptides or a so-called supramolecular polymer. As a result, the conjugates of these CP and amphiphilic polymer blocks self-assemble into tubisomes independent of the ratio of the attached hydrophilic and hydrophobic polymers, while the respective pristine block copolymers vary in their micelle shape. Cylinder lengths of 200 nm to 400 nm and core radii between 8 nm to 10 nm are obtained which solely depends on the size of the hydrophobic block.