Realignment of Bottlebrush Segments Induces the Contraction of Individual Polymer Vesicles

The shape transformation of polymer vesicles is of great importance for biorelevant applications as well as for understanding cellular shape adaptation. However, realizing shape transformation in a controlled manner by rationally manipulating the molecular geometry of the building block is still challenging. Herein, we reported a controlled contraction process of individual polymer vesicles via the realignment of bottlebrush segments by using a linear-alt-bottlebrush alternating multiblock copolymer (LBAMBCP) as the building block. The well-defined LBAMBCPs, A50[(xbB)mA50]n (x = 1 and 3 refer to the grafting density, m = 10, 20, and 30, n = 1, 3, and 5), that consisted of the xbB segment of bottlebrush with varied grafting densities (x) of PS branches and the A segment of linear poly[norbornene-oligopoly(ethylene glycol)] (poly(NB-OEG)) were first synthesized. To perform the self-assembly in a selective solvent of poly(NB-OEG) segments, we found that these LBAMBCPs with a high grafting density (x = 3) of PS branches promoted the formation of vesicular structures, and typical hollow vesicles with an average size over 600 nm were produced. It was observed that the vesicles formed by 7- and 11-LBAMBCPs A50[(3bB)10A50]n (n = 3 and 5) could further undergo the contraction of individual vesicles to evolve into compound vesicles with a steady reduction in size by the realignment of bottlebrush segments in the vesicle wall. The contraction process was confirmed to be strongly related to the number and grafting density of bottlebrush segments and could be simply regulated by changing the initial concentration and solvent composition. Overall, we provide a fresh case for the controlled contraction of individual vesicles by manipulating the molecular geometry of the building blocks.