Multilayered Polymersome Formed by Amphiphilic Asymmetric Macromolecular Brushes

Abstract

Well-defined amphiphilic asymmetric macromolecular brushes were synthesized recently and were able to self-assemble into vesicles in selective solvents. The self-assembly of polymer brushes consisting of a solvophobic backbone attached with two different side chains, solvophilic and amphiphilic diblock, is explored by dissipative particle dynamics. Dependent on the block length, molecular architecture, and grafting density, the multicompartment aggregate exhibits a rich variety of morphological conformations, including five types of vesicles: porous aggregates, worm-like micelles, donut micelles, hamburger micelles, and unimolecular micelles. For certain polymer brushes, atypical polymersomes with asymmetric multilayered membranes are spontaneously formed. In addition, temperature variation induced morphological transformation from an asymmetric four-layered polymersome to a symmetric seven-layered polymersome is observed for polymer brushes containing a thermoresponsive block. Consequently, the resulting polymersome decreases in size quite sharply as temperature exceeds lower critical solution temperature. These simulation findings are consistent with experimental observations. By varying the lengths of various blocks, the morphological phase diagram and internal structures of the resulting aggregates are obtained. At a fixed composition of polymer brushes, the aggregate morphology varies with the structural arrangement of the two solvophilic blocks in the molecule. Asymmetric polymersomes are formed when the two solvophilic blocks are separately attached to the backbone and side chain. Although asymmetric vesicles are observed at moderate grafting density, unique donut aggregates are formed for high density but hamburger micelles develop at low density.