Metallo‐supramolecular block copolymer micelles: Improved preparation and characterization

Abstract

Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis‐(2,2′:6′,2″‐terpyridine‐ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two “protomer”‐type micelles: PS20‐[Ru]‐PEO70 and PS20‐[Ru]‐PEO375. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS20‐[Ru]‐PEO70 micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (dh) of 18 nm. For PS20‐[Ru]‐PEO375 micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and dh = 34 nm. The latter particles were found to be identical to the “equilibrium” micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4458–4465, 2004

Monte Carlo Simulations of Metallo‐Supramolecular Micelles

“…[15] Dynamic light scattering [13] and cryo-TEM experiments [16] revealed a strong tendency of metallo-supramolecular micelles to aggregate in contrast to the analogous traditional diblock copolymer micelles, a phenomenon that can be suppressed by modifying the method of preparation of the micelle. [17] Unless metallo-supramolecular micelles were prepared in salt-screened solutions, their core size does not scale linearly with the degree of polymerization of core-forming blocks as expected from the classical theory for traditional micelles. [18] Metallo-supramolecular micelles are relatively stable in water and various organic solvents [13] due to the large binding constant of the terpyridine-ruthenimum complexes and high glass transition temperature for the core-forming block.…”

Using Metallo‐Supramolecular Block Copolymers for the Synthesis of Higher Order Nanostructured Assemblies

“…The groups of Schubert, Gohy, and coworkers [39,43,90] have shown that, as for covalent analogues, amphiphilic AB metallo-block copolymers can self-assemble, to give various metal containing micellar architectures in solution. Their first report in this area detailed the self-assembly of a bis-terpyridine Ru(II) linked PS-b-PEO block copolymer (PS 20 -[Ru]-PEO 70 ) into spherical micelles, induced via the addition of a non-solvent for one of the blocks ( Figure 6).…”

“…Thus, in theory, upon self-assembly into triblock micelles, cross-linking to give nanoparticles and subsequent selective PS core removal, the targeted core hollowed, hydrophobic nanocages incorporating a new PMA internal shell layer could be accessed. An asymmetric SCS Pd(II) pyridine complex linked triblock terpolymer was synthesized with the structure: poly(acrylic acid)-b-poly(methyl acrylate)-[Pd)-PS or PAA 90 -PMA 45 -[Pd)-PS 35 , upon polymerization with functional CRP initiator species. [48] This strategy relies upon the established complexation chemistries of the previous system, but utilizes reversible addition fragmentation chain transfer (RAFT) polymerization to synthesize a covalently linked amphiphilic diblock (PAA 90 -PMA 45 -[Pd) which, when complexed to a second block bearing a pyridine functionality, Figure 11.…”

“…65 nm) which showed no further aggregation. [90] Further investigations into their micellization behavior utilized a library of block copolymers of the type: PS x -[Ru]-PEO y with varying block lengths (x and y). They found that, unlike the classical theory for covalent amphiphilic copolymers, the micelle size did not scale linearly with respect to the degree of polymerization (DP) of the PS core block.…”

Hybrid metal–polymer composites from functional block copolymers

“…[68][69][70][71] Related end-functional polymers have been used for the stabilization of metallic nanoparticles either by polymer growth from initiators attached to the nanoparticle surface 72,73 or by the mixing of preformed end-functional polymers with nanoparticles. 60 Although such systems are of great potential use, the remainder of this highlight focuses on those systems in which metal species are complexed to highly functionalized polymer blocks.…”