Controlling vesicle formation via interpolymer hydrogen-bonding complexation between poly(ethylene oxide)-block-polybutadiene and poly(acrylic acid) in solution

This paper describes a controllable vesicle formation of a diblock copolymer of poly( ethylene oxide)-block-polybutadiene (PEO-b-PB) and a homopolymer of poly(acrylic acid) (PAA) in a solvent mixture of THF and n-dodecane. The number-average molecular weights (M-n) of both the PEO and PB blocks are 5100 g/mol; the weight-average molecular weight (M-w) of the PAA is similar to 2000 g/mol. The assembly is driven by the hydrogen-bonding complexation between the complementary binding sites on PEO and PAA. The vesicles can load PAA far above the stoichiometrical monomer ratio of PAA to PEO ([AA]/[EO]). At 0.85 <= [AA]/[EO] <= 2.5, unilamellar vesicles (ULVs) with a constant membrane thickness of 16 nm are obtained in a controllable manner, of which the surface area increases linearlywith [AA]/[EO]. Further increasing [AA]/[EO] above 3 results in the formation of multivesicular vesicles (MVVs). The PAA chains in ULVs are uniformly inserted into membranes with a direction preferentially perpendicular to the interface. When the PB blocks are unable to sufficiently cover the interface and the PEO blocks do not interact homogeneously with PAA chains, the MVVs form.