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A novel method was developed to prepare shell-cross-linked knedel-like structures (SCK's), which are double-layered polymer nanospheres, in a convenient three-step procedure:  (1) polystyrene-b-poly(acrylic acid) ((DP n )PS = 130, (DP n )PAA = 120) copolymer was prepared by sequential anionic polymerization of styrene and tert-butyl acrylate, followed by hydrolysis; (2) the amphiphilic block copolymer was allowed to self-assemble into spherical multimolecular micelles in a water and THF solvent mixture; (3) the poly(acrylic acid), comprising the shells of micelles, was cross-linked by amidation using several di- and multiamino linkers (2,2‘-(ethylenedioxy)bis(ethylamine), hexakis(ethylene glycol)diamine, hexamethylenediamine, and triethylenetetramine). The extent of cross-linking was controlled by the relative amount of cross-link reagent used. The SCK's were spherical, core−shell structures composed of polystyrene cores and cross-linked hydrogel-like shells. The sizes, shapes, and structural differences between the polymer micelles and the SCK's were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) in aqueous solution. The non-cross-linked polymer micelles deformed substantially upon adsorption onto mica and became ellipsoidal upon drying on a carbon surface, whereas the SCK's remained as stable, spherical structures under all conditions. The polymer micelles had a number average height of 17 nm from AFM and 26 nm diameter from TEM, while the SCK's prepared from 2,2‘-(ethylenedioxy)bis(ethylamine) cross-linkers had a number average height of 24 nm from AFM and a number average diameter of 28 nm from TEM. The SCK shell thickness swelled 2−3-fold in water, as determined from comparison of the number average diameter obtained by DLS (37 nm) with that by TEM. Spectroscopic methods and thermal analysis were utilized to further characterize the SCK's.

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.

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An emulsion process has been developed for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solvents. The process entails formation of emulsion particles with a mean hydrodynamic diameter of 150 nm and consisting of a water-soluble organic solvent (e.g., 2-butoxyethanol), a water-insoluble organic acid (e.g., dinonylnaphthalenesulfonic acid), aniline, and water. Aniline is protonated by the organic acid to form a salt which partitions into the organic phase. As oxidant (ammonium peroxydisulfate) is added to the reaction mixture, PANI intermediates are formed in the organic phase. As the reaction proceeds, the emulsion flocculates, forming a two-phase system. The reaction features an induction period followed by an exothermic polymerization, at which time soluble PANI forms in the organic phase. The reaction progress is conveniently monitored by temperature, pH, and open circuit potential. When dinonylnaphthalenesulfonic acid (DNNSA) is employed as the organic acid, the resulting product is highly soluble in organic solvents such as xylene and toluene (not a dispersion), has high molecular weight (M w > 22 000), and forms moderately conductive (10-5 S/cm) films. We have also found that the conductivity of PANI−DNNSA films may be enhanced (up to 5 orders of magnitude) by treating the films with surfactants such as benzyltriethylammonium chloride (BTEAC) or low-molecular-weight alcohols and ketones such as methanol and acetone. Electron microscopy shows that the conductivity enhancement phenomenon observed upon treatment with surfactants is due to self-assembly of PANI−DNNSA molecules into an interconnected network morphology. In the case of alcohol or ketone treatment the film conductivity is enhanced due to extraction of excess dopant, densification of the polymer, and a concomitant increase in crystallinity.