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

ABSTRACT: Chloromethyl groups were introduced into the polystyrene (PS) blocks of hydrogenated poly(styreneblock-butadiene-block-styrene) (SEBS) via Friedel-Crafts reaction. The product (SEBS-CH 2 Cl) formed spherical micelles with PS corona and hydrogenated PB core in THF/ethanol (10/9, v/v). Then, the polystyrene corona carrying CH 2 Cl groups was cross-linked by amination with 1,6-hexanediamine as a cross linker. The shell cross-linked micelles showed spherical core-shell structure and were stable in solution, which was verified by DLS in solution and by TEM in the solid state. KEY WORDS poly(styrene-block-butadiene-block-styrene) (SEBS) / Shell Cross-Linked Micelle / Chloromethylation / Amination / The creation of novel polymeric nanomaterials with the appropriate morphologies and functions for potential applications has become an intensely studied field of nanotechnology. Recently Wooley and coworkers have reported the synthesis of shell crosslinked "knedel" (SCK) micelles. 1-5 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. Currently, the precursors for SCK's are mainly the block copolymers with a cross-linkable block. All the copolymers were prepared in laboratories by living polymerization, particularly, sequential anionic polymerization. EXPERIMENTAL Materials Monodisperse SEBS (G1652, Shell Co) with M n = 52500, M w /M n ≤ 1.06, and 28.6 wt% styrene units was used as the starting material. 1,6-Hexanediamine was used as the cross linker. SnCl 4 , trioxane, and chlorotrimethylsilane were purified by routine methods. Chloromethylation of SEBS and Characterization To avoid cross-linking and degradation of SEBS in the process of chloromethylation, saturation of the residue double bonds in the EB block was performed via successive bromination and hydrogenolysis according to the procedures reported previously