Media-modulated Inter-chain Or Intra-chain Coordination Of Amphiphilic Block Copolymer Micelles

Hybrid nanoparticles have received a great deal of attention because of their useful applications in catalysis, optics, data storage, biosensing, medical diagnostics and controlled drug release. The controlled assembly of these nano-scaled functional materials from molecular entities is a key issue for the future developments. Nature endows us with numerous fine models of self-assembled functional hybrid nanoparticles. Inspired by the coordination mode tunability of natural zinc proteins, this paper describes a new type of polymer micelles, whose coordination mode may be finely tuned simply via adjusting the solution media. A well-defined amphiphilic poly[N-(6-(3,5-di-tert-butyl-2-hydroxyl- benzylideneamino)hexyl)methacrylamide]-block-poly(2-hydroxyethylmethacrylate) copolymer (PDBHHMA-b-PHEMA) was synthesized via a rapid and well-controlled visible light activating RAFT polymerization at 25 oC, and a subsequent reaction with 3,5-di-tert-butyl-2-hydroxybenzaldehyde. 1H NMR and GPC analyses indicated the intact structure, well-defined molecular weight and narrow distribution of this block copolymer. PDBHHMA32-b-PHEMA120 could self-assemble into small-sized PDBHHMA-core micelles in methanol, or large-sized inversed PDBHHMA-shell micelles in dichloromethane. Both types of micelles could coordinate with cobalt ions in the whole PDBHHMA micellar shells or cores. This coordination proceeded much more rapidly in PDBHHMA micellar shells than in PDBHHMA micellar cores. The hydrodynamic diameters of both types of micelles kept essentially constant upon coordination. The coordination in micellar cores led to the linear increase of light scattering intensity up to a saturated point of [Co2+]:[DBHHMA]=0.4:1, but no intensity variation was detectable upon coordination in micellar shells, even large excess of cobalt ions added. The addition of small amount of DMF significantly accelerated the coordination of micellar cores but brought down the intensity increase tendency. Both DLS and GPC results evidenced the interchain coordination mode of micellar cores, the addition of small amount of DMF clearly led to the intrachain coordination tendency because of the co-solvation effect. In contrast, the coordination of micellar shells was predominantly in intrachain coordination mode. These novel media-tunable coordination behaviors are desirable not only in the chem-related fields such as catalysts or nanoreactors, but also for the bio-related applications for biosensors or drug carriers.