Synthesis and Solution Self-assembly of Amphiphilic Molecular Bottlebrushes

Well-defined AbBA triblock bottlebrushes with the poly(N,N'-dimethyl acrylamide) (PAm) as A block and polyacrylate densely grafted with polystyrene (PS) as B block were prepared by the combination of controlled radical polymerization and copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The composition and structure of the bottlebrushes were confirmed by hydrogen nuclear magnetic resonance ((HNMR)-H-1) and gel permeation chromatograph (GPC), which showed a high side-chain grafting density of about 100%. The self-assembly behavior of the bottlebrushes with different PAm contents was investigated under various conditions. The morphologies of assemblies were observed using transmission electron microscope (TEM). Under the identical condition, the amphiphilic bottlebrushes with higher PAm content (>5%) self assembled into sphere micelles, while the bottlebrushes with lower PAm content trended to form lamellar micelles and vesicles. The effects of initial concentration and solvents were investigated using PAm195-b-(PA-g-PS67)(153)-PAm195 under different conditions. The increase of the initial concentration changed the micelles from spheres to lamellae/vesicles. A common solvent with the solubility parameter closer to PS increased the mobility of the PS chains in the core, and led to assemblies of vesicles (thermodynamics steady state); while a selective solvent with the solubility parameter differed greatly from PS led to aggregation to form larger vesicles.