Amphiphilic cylindrical core-shell brushes via a "grafting from" process using ATRP

Atom transfer radical polymerization (ATRP) was applied to the synthesis of amphiphilic cylindrical polymer brushes by using the "grafting from" techn ique. The procedure included the following steps: (1) ATRP of 2-hydroxyethy l methacrylate (HEMA) gave well-defined poly(HEMA), (2) subsequent esterifi cation of the pendant hydroxy groups of poly(HEMA) with 2-bromoisobutyryl b romide yielded a polyinitiator, poly(2-(2-bromoisobutyryloxy)ethyl methacry late (PBIEM), (3) ATRP of various monomers (tent-butyl acrylate, or styrene ) using PBIEM as polyinitiator yielded cylindrical brushes with homopolymer side chains, (4) addition of a second monomer (styrene or tent-butyl acryl ate) formed the cylindrical brushes with diblock copolymer side chains (cor e-shell cylinders), and (5) hydrolysis of the poly(tert-butyl acrylate) (Pt BA) block of the side chains to poly(acrylic acid) (PAA) formed amphiphilic core-shell polymer brushes. By using this technique, well-defined core-she ll cylindrical polymer brushes with polystyrene (PS), PtBA, PS-b-PtBA, PtBA -b-PS, PS-b-PAA, or PAA-b-PS as side chains were successfully synthesized. The molecular weights and radii of gyration of the polymer brushes were obt ained by static light scattering in THF. The absence of inter/intra-macromo lecular coupling reactions during ATRP synthesis was confirmed by GPC, NMR, and MALDI-TOF analyses of the side chains and scanning force microscopy (S FM). Single wormlike unimolecular nanocylinders are clearly visualized on a mica surface while aggregates are usually observed on a SiOx surface. The brushes with PS-b-PtBA side chains were hydrolyzed to PS-b-PAA side chains forming unimolecular wormlike micelles. These unimolecular micelles showed a unique response to solvent quality, as indicated by H-1 NMR and dynamic l ight scattering.