Prismatic Block Copolymer Hexosomes

Cubosomes and hexosomesare recent solution morphologies with anordered porous structure and are observed for lipids and amphiphilicblock copolymers (BCPs) with high hydrophobic fractions. Whereas lipidhexosomes typically exhibit a prismatic shape, BCP hexosomes haveso far only been observed as closed microspheres where inner channelsare not connected to the surrounding medium. Here, we describe theformation of flat, prismatic BCP hexosomes with pronounced facetingand a highly ordered lattice of hexagonally packed channels. We assemblepolystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP or SV) into the hexosome framework using polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT) as a macromolecular surfactant in low-& chi;solvents. During solvent exchange, SV-rich domains form through liquid-liquidphase separation, followed by solidification and confined assemblywithin these domains. Since the final solvent (acetone) has a verylow & chi; parameter toward PS and P4VP (equaling low interfacialtension), solidification of the hexosome occurs under confinementconditions that we term "supersoft". The low interfacialtension allows the stabilization of the hexagonal-prismatic shape,which originates from the hexagonal lattice of channels. Increasingthe interfacial tension with polar cosolvents at some point dominatesthe particle shape, resulting in deformation of prismatic BCP hexosomesinto spinning-top structures. The use of low-& chi; solvents forconfined assembly of BCPs may allow the formation of unusual particleshapes simply by tuning the polymer-solvent interaction.