| Abstract
| - A novel method was developed to prepare shell-cross-linkedknedel-like structures (SCK's), which aredouble-layered polymer nanospheres, in a convenient three-stepprocedure: (1) polystyrene-b-poly(acrylicacid)((DPn)PS = 130,(DPn)PAA = 120) copolymer wasprepared by sequential anionic polymerization of styreneandtert-butyl acrylate, followed by hydrolysis; (2) theamphiphilic block copolymer was allowed to self-assembleintospherical multimolecular micelles in a water and THF solvent mixture;(3) the poly(acrylic acid), comprising theshells of micelles, was cross-linked by amidation using several di- andmultiamino linkers (2,2‘-(ethylenedioxy)bis(ethylamine), hexakis(ethylene glycol)diamine,hexamethylenediamine, and triethylenetetramine). The extentofcross-linking was controlled by the relative amount of cross-linkreagent used. The SCK's were spherical, core−shell structures composed of polystyrene cores and cross-linkedhydrogel-like shells. The sizes, shapes, andstructuraldifferences between the polymer micelles and the SCK's were studied byatomic force microscopy (AFM), transmissionelectron microscopy (TEM), and dynamic light scattering (DLS) inaqueous solution. The non-cross-linked polymermicelles deformed substantially upon adsorption onto mica and becameellipsoidal upon drying on a carbon surface,whereas the SCK's remained as stable, spherical structures under allconditions. The polymer micelles had a numberaverage height of 17 nm from AFM and 26 nm diameter from TEM, while theSCK's prepared from2,2‘-(ethylenedioxy)bis(ethylamine) cross-linkers had anumber average height of 24 nm from AFM and a numberaverage diameter of 28 nm from TEM. The SCK shell thicknessswelled 2−3-fold in water, as determined fromcomparison of the number average diameter obtained by DLS (37 nm) withthat by TEM. Spectroscopic methodsand thermal analysis were utilized to further characterize theSCK's.
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