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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.

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The preparation and characterization of macromolecular nanostructures possessing an amphiphilic core-shell morphology with a hydrophobic, fluidlike core domain with a low glass-transition temperature are described. The nanostructures were prepared by the self-assembly of polyisoprene-b-poly(acrylic acid) diblock copolymers into polymer micelles, followed by crosslinking of the hydrophilic shell layer via condensation between the acrylic acid functionalities and 2,2Ј-(ethylenedioxy)bis(ethylamine), in the presence of 1-(3Ј-dimethylaminopropyl)-3-ethylcarbodiimide methiodide. The properties of the resulting shell-crosslinked knedel-like (SCK) nanoparticles were dependent on the microstructure and properties of the polyisoprene core domain. SCKs containing polyisoprene with a mixture of 3,4-and 1,2-microstructures underwent little shape distortion upon adsorption from aqueous solutions onto mica or graphite. In contrast, when SCKs were composed of polyisoprene of predominantly cis-1,4-repeat units, the glass-transition temperature was Ϫ65°C, and the nanospheres deformed to a large extent upon adsorption onto a hydrophilic substrate (mica). Adsorption onto graphite gave a less pronounced deformation, as determined by a combination of transmission electron microscopy and atomic force microscopy. Subsequent crosslinking of the core domain (in addition to the initial shell crosslinking) dramatically reduced the fluid nature and, therefore, reduced the SCK shape change.

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