Metallo-supramolecular block copolymer micelles: improved preparation and characterization

Micelles prepd. 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 prepn. procedure developed, which is described here, was used to prep. two \"protomer\"-type micelles: PS20-[Ru]-PEO70 and PS20-[Ru]-PEO375. The dropwise addn. of water to a soln. of the compds. in DMF was replaced by the controlled addn. of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equil. analyses in an anal. ultracentrifuge and by transmission electron microscopy of neg. stained samples. Sedimentation anal. showed virtually unimodal size distributions, in contrast to the findings on micelles prepd. previously. PS20-[Ru]-PEO70 micelles were found to have an av. molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle prepn. by the std. method) and an av. hydrodynamic diam. (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 \"equil.\" micelles prepd. 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 diams. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity anal. The findings from electron microscopy were in disagreement with those from the sedimentation anal. both in av. micelle diam. and in the width of the distributions, apparently because of imperfections in the staining procedure. The prepn. procedure described also may be useful in micelle formation from other types of protomers. [on SciFinder (R)]