Hydrogel-Coated Glassy Nanospheres:  A Novel Method for the Synthesis of Shell Cross-Linked Knedels

Abstract

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.

Packaging of DNA by shell crosslinked nanoparticles

“…DLS measurements (29) confirmed that the SCK/DNA aggregates formed while in solution and provided for The hydrodynamic diameter distribution of the DNA used to prepare SCK/DNA complexes was also characterized by DLS. Unlike the SCK component of the complexes, the diameter distribution of the DNA component was extremely broad.…”

Double Hydrophilic Block Copolymer Monolayer Protected Hybrid Gold Nanoparticles and Their Shell Cross-Linking

“…If one block bears reactive functional groups, the morphologies of the aggregates can be fixed by chemical cross-linking. [32][33][34] In particular, shell cross-linked (SCL) micelles combine the properties of micelles, microgels, nanoparticles, and dendrimers, and various applications such as targeted drug delivery, sequestration of metabolites, and entrapment of environmental pollutants have been suggested. [35][36][37][38][39] The first example of SCL micelles was described by Wooley and co-workers, who oligomerized pendent styrene groups by using free radical polymerization chemistry.…”

Preparation and Morphologies of Shell Cross-Linked Micelles Based on Commercial Poly(styrene-block-ethylene-co-butene-block-styrene)

“…All the copolymers were prepared in laboratories by living polymerization, particularly, sequential anionic polymerization. [1][2][3][4][5][6][7][8][9][10] However, the preparation of such re- † To whom correspordence should be addressed. quired block copolymers is usually costly and timeconsuming.…”

“…Recently Wooley and coworkers have reported the synthesis of shell crosslinked "knedel" (SCK) micelles. [1][2][3][4][5] SCK's belong to a new class of nanomaterials which resemble polymer micelles in their core-shell morphology as well as dendrimers and arborescent polymers in being covalently bound and stable structures. 2 Various applications in areas as diverse as solubilization, catalysis, fillers, coatings, and delivery have been proposed for these fascinating new materials.…”