Media-modulated interchain or intrachain coordination of amphiphilic block copolymer micelles

摘要

Inspired by the tunability of coordination mode of natural zinc proteins, this paper describes a new type of polymer micelle, whose coordination mode may be finely tuned simply via adjusting the solution media. To this end, a well-defined poly[N-(6-(3,5-di-tert-butyl-2-hydroxybenzylideneamino)hexyl) methacrylamide]-block-poly(2-hydroxyethyl methacrylate) (PDBHHMA-b-PHEMA) amphiphilic block copolymer was synthesized via rapid and well-controlled visible light activating RAFT polymerization at 25 °C and subsequently directly reacted with 3,5-di-tert-butyl-2-hydroxybenzaldehyde. ~1H NMR and GPC analyses indicate the intact structure, well-defined molecular weight, and narrow distribution of PDBHHMA_(32)-b-PHEMA_(120). PDBHHMA_(32)-b-PHEMA_(120) may self-assembles into small PDBHHMA-core micelles in methanol or large inversed PDBHHMA-shell micelles in dichloromethane. Cobalt ions coordinate with the functionalities of PDBHHMA blocks in whole micellar shells or cores. The coordination of DBHHMA units in micellar shells proceeds much more rapidly than in micellar cores. The addition of small amount of DMF may significantly accelerate the coordination process in micellar cores. Although this coordination has a negligible effect on the sizes of both types of spherical micelles, coordination in micellar cores leads to a linear increase of light scattering intensity up to a critical feed molar ratio of [Co~(2+)]_0/[DBHHMA]_0 = 0.4, whereas coordination in micellar shells does not influence light scattering intensity, even large excess of cobalt ions added, e.g., [Co~(2+)] _0/[DBHHMA]_0 = 0.7. In micellar cores, cobalt ions tend to coordinate with DBHHMA units in interchain mode; N,N-dimethylformamide (DMF) cosolvent may accelerate this coordination process but increase the tendency of intrachain coordination. On the contrary, coordination in micellar shells occurs predominantly in intrachain mode. These media-tunable coordination modes finely tune the stability of micelles in their nonselective good solvent DMF.