Topological Structure-Induced Self-Assembly of Highly Asymmetric PLLA-b-QPDMAEMA Block Copolymers in Solution: Linear Versus Bottlebrush

During self-assembly process of block copolymers in solution, when the volume fraction of solvophobic blocks is too low, usually below 10%, the copolymers generally tend to dissolve, which has caused trouble. Herein, a bottlebrush block copolymer composed of poly(L-lactic acid) (PLLA) and quaternized poly(N,N-dimethylaminoethylmethacrylate) (QPDMAEMA), whose content of solvophobic block PLLA was below 2 wt%, was prepared. Owing to the rigidity derived from the advantages of topological structure of bottlebrush-like molecules, the interfacial curvature between two incompatible microphases is maintained, and this highly asymmetric copolymer unexpectedly spontaneously assembles into uniform spherical micelles with diameters of tens of nanometers. The morphology of aggregates was verified by dynamic light scattering, transmission electron microscopy and atomic force microscope. This study expands the understanding of traditional theory about copolymers self-assembly in solution, which helps to design, prepare, and apply polymer micelles with various structures from a broader perspective.