Nonionic Amphiphilic Linear Dendritic Block Copolymers. Solvent-Induced Self-Assembly and Morphology Tuning

摘要

In this article, we report the solution self-assembly of a series of amphiphilic linear-dendritic block copolymers (LDBCs), which are composed of hydrophilic dendritic poly(ether-ester), PEE, blocks based on 2,2-bis(hydroxymethyl)propionic acid and hydrophobic linear poly(styrene), PSt, blocks. The investigated LDBCs have narrow dispersity with three PEE generations (1-3) and a broad range of PSt molecular masses and are produced by dendron-initiated atom transfer radical polymerization of styrene followed by deprotection of the peripheral dendron hydroxyl groups. The solution self-assembly of the copolymers is performed by slowly adding water to the polymer solution in tetrahydrofuran (THF) as the common solvent for both blocks of the copolymers. The morphologies of the supramolecular assemblies are preserved either by diluting their dispersion by excess of water or by THF evaporation. It is found that the micellar morphology (sphere, wormlike, and/or vesicle) depends on the hydrophilic block fraction (F-pEE) and dendron generation. The self-assembly morphology transition from vesicle to wormlike micelle or sphere is achieved by switching the common solvent from THF to dimethylformamide. Interestingly, LG2-PSt 18k forms a bicontinuous phase, while LG3-PSt 68k forms onion-like aggregates with acetone as the common solvent. Palladium complexation within the dendron block leads to formation of cubosomes and other structures with morphology of higher order.