Amphiphilic Cylindrical Core−Shell Brushes via a “Grafting From” Process Using ATRP

Abstract

Atom transfer radical polymerization (ATRP) was applied to the synthesis of amphiphilic cylindrical polymer brushes by using the “grafting from” technique. The procedure included the following steps: (1) ATRP of 2-hydroxyethyl methacrylate (HEMA) gave well-defined poly(HEMA), (2) subsequent esterification of the pendant hydroxy groups of poly(HEMA) with 2-bromoisobutyryl bromide yielded a polyinitiator, poly(2-(2-bromoisobutyryloxy)ethyl methacrylate (PBIEM), (3) ATRP of various monomers ( tert -butyl acrylate, or styrene) using PBIEM as polyinitiator yielded cylindrical brushes with homopolymer side chains, (4) addition of a second monomer (styrene or tert -butyl acrylate) formed the cylindrical brushes with diblock copolymer side chains (core−shell cylinders), and (5) hydrolysis of the poly( tert -butyl acrylate) (P t BA) block of the side chains to poly(acrylic acid) (PAA) formed amphiphilic core−shell polymer brushes. By using this technique, well-defined core−shell cylindrical polymer brushes with polystyrene (PS), P t BA, PS - b -P t BA, P t BA - 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 obtained by static light scattering in THF. The absence of inter/intra-macromolecular coupling reactions during ATRP synthesis was confirmed by GPC, NMR, and MALDI−TOF analyses of the side chains and scanning force microscopy (SFM). Single wormlike unimolecular nanocylinders are clearly visualized on a mica surface while aggregates are usually observed on a SiO x surface. The brushes with PS- b -P t BA 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 1 H NMR and dynamic light scattering.