Spiral- and meridian-patterned spheres self-assembled from block copolymer/homopolymer binary systems

Spiral nanostructures, mainly in the 2D form, have been observed in polymer self-assembly, while well-defined 3D spirals are rarely reported. Here we report that a binary system containing polypeptide-based block copolymers and homopolymers can self-assemble into well-defined spiral spheres (3D spirals), in which the homopolymers form the core and the copolymers form the spirals. Upon increasing the preparation temperature, meridian spheres were obtained. Mixing polypeptide block copolymers with opposite backbone chirality also leads to the formation of meridian spheres. In the meridian patterns, a tighter packing manner of the phenyl groups appended to the polypeptide blocks was observed, which is responsible for the spiral-to-meridian transitions. This work enriches the research of spiral assemblies and provides a facile route to switch chiral/achiral nanostructures by regulating the packing manner of the pendant groups. Spiral spheres are self-assembled from a binary system of rod-coil block copolymers and homopolymers, and a spiral-to-meridian pattern transition achieved by increasing temperature is attributed to a tighter packing of the block copolymers.