A stable phase of toroidal, or ringlike, supramolecular assemblies was formed by combining dilute solution characteristics critical for both bundling of like-charged biopolymers and block copolymer micelle formation. The key to toroid versus classic cylinder micelle formation is the interaction of the negatively charged hydrophilic block of an amphiphilic triblock copolymer with a positively charged divalent organic counterion. This produces a self-attraction of cylindrical micelles that leads to toroid formation, a mechanism akin to the toroidal bundling of semiflexible charged biopolymers such as DNA. The toroids can be kinetically trapped or chemically cross-linked. Insight into the mechanism of toroid formation can be gained by observation of intermediate structures kinetically trapped during film casting.

Core-shell brush copolymers were prepared on the basis of a tandem synthetic strategy and used as single molecular templates for the preparation of polymeric nanomaterials. An alkoxyamine-functionalized norbornene monomer was prepared and then polymerized by ring-opening metathesis polymerization. The well-defined polymer (Mn = 122 kDa, Mw/Mn = 1.13) contained one alkoxyamine functionality per repeat unit and was then used as a polyfunctional macroinitiator for sequential nitroxide-mediated radical polymerizations of isoprene and tert-butyl acrylate. The resulting well-defined brush copolymer (Mn = 1410 kDa, Mw/Mn = 1.23) was transformed to an amphiphilic core-shell brush copolymer comprising poly(isoprene)-b-poly(acrylic acid) grafts by hydrolysis. Subsequent cross-linking of the poly(acrylic acid) block segments afforded peripherally cross-linked brush copolymer nanostructures, which served, finally, as templates for hollowed nanoscale frameworks by ozonolysis of the poly(isoprene)-based cores. Each transformation led to dramatic changes in the nanoscale composition and structure which were detected by combinations of spectroscopic measurements, atomic force microscopy imaging in the solid state, and/or dynamic light-scattering characterization in aqueous solution.

Shell cross-linked nanoparticles (SCKs) presenting surface- and bioavailable biotin functional groups were synthesized via a mixed micelle methodology, whereby co-micellization of chain terminal biotinylated poly(acrylic acid)-b-poly(methyl acrylate) (PAA-b-PMA) and nonbiotinylated PAA-b-PMA were cross-linked in an intramicellar fashion within the shell layer of the mixed micelles, between the carboxylic acid groups of PAA and the amine functionalities of 2,2'-(ethylenedioxy)diethylamine. The hydrodynamic diameters (D(h)) of the micelles and the SCKs with different biotinylated block copolymer contents were determined by dynamic light scattering (DLS), and the dimensions of the SCKs were characterized with tapping-mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The amount of surface-available biotin was tuned by varying the stoichiometric ratio of the biotinylated PAA-b-PMA versus the nonbiotinylated PAA-b-PMA, as demonstrated with solution-state, binding interaction analyses, an avidin/HABA (avidin/4'-hydroxyazobenzene-2-carboxylic acid) competitive binding assay, and fluorescence correlation spectroscopy (FCS). The avidin/HABA assay found the amount of available biotin at the surface of the biotinylated SCK nanoparticles to increase with increasing biotin-terminated block copolymer incorporation, but to be less than 25% of the theoretical value. FCS measurements showed the same trend.