Block-copolymer-free strategy for preparing micelles and hollow spheres: Self-assembly of poly(4-vinylpyridine) and modified polystyrene

Noncovalently connected micelles (NCCM) with poly(4-vinylpyridine) (PVPy) as the shell and hydroxyl -containing polystyrene, i.e., PS(OH), as the core were formed in a selective solvent mixture for PVPy by inter-polymer hydrogen bonding. With increase in the hydroxyl content in PS(OH), the structure of the micelles changed from perfect spheres to rodlike and then networklike aggregates. Shell-cross-linked micelles and then hollow spheres were obtained based on the NCCM, with hydrogen bonding rather than covalent bonds between the core and shell. The shell structure was locked in by the reaction of PVPy with the cross-linker of 1,4-dibromobutane, under mild conditions, Cavitation of the spherical micelles was realized just by changing the medium from the selective solvent to a common one to dissolve PS(OH) chains in the interior of the micelles, The resultant spheres were proved to be hollow by TEM observation and by both static and dynamic light scattering, The thickness of the shell could be controlled by changing the micelle composition. DLS, TEM, SEM, and AFM studies demonstrated that the integrity of the assembled spheres was maintained during the cross-linking and cavitation, The size of the hollow spheres increased apparently with dilution of the solution. Compared to the conventional route to shell-cross-linked micelles and hollow spheres from the micelles made of block copolymers, the current approach has the significant advantages of avoiding synthesis of block copolymers and chemical degradation of the core components.