Synthesis, characterization, and properties of ABA type triblock copolymer brushes of styrene and methyl acrylate prepared by atom transfer radical polymerization

A tethered triblock copolymer has been synthesized by sequential monomer addition to a self-assembled monolayer of (11- (2-bromo-2-methyl)propionyloxy) undecyltrichlorosilane. Si/SiO2// polystyrene-b-poly(methyl acrylate)-b-polystyrene (PS-b-PMA-b-PS) and Si/SiO2//PMA-b-PS-b-PMA were prepared by the "grafting from" method using atom transfer radical polymerization. The resulting triblock brushes were characterized by ATR-FTIR, water contact angles, ellipsometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Free polymer formed during the brush formation was characterized by gel permeation chromatography. Treatment of the triblock brushes with blockselective solvents caused reversible changes in the water contact angles and AFM. AFM analysis revealed a patterned nanomorphology when the brush was treated with a good solvent for the mid-block. We have interpreted this nanomorphology in terms of a folded brush structure where the two end blocks aggregate and force the mid-block to the air interface, XPS and water contact angle observations are consistent with this interpretation.