Anionic Synthesis of Block Copolymer Brushes Grafted from a 1,1-Diphenylethylene Monolayer

Abstract

A new method to prepare diblock copolymer brushes on oxide surfaces by anionic polymerization has been developed using a surface bound 1,1-diphenylethylene monolayer. Properties of the brushes were characterized by X-ray photoelectron spectroscopy (XPS), AFM, FTIR-ATR, X-ray reflectometry, and contact angle measurements. Films of thickness as high as 24 nm (by ellipsometry) were obtained by a “grafting from” strategy. Reacting a covalently attached monolayer of 1,1-diphenylethylene units with n -butyllithium created an initiator layer for the “grafting from” strategy. The corresponding 1,1-diphenylhexyllithium derivatives initiated the polymerization of a smooth brush of polyisoprene. AFM measurements of polyisoprene brushes indicated a surface microroughness of 0.3−0.5 nm (rms). The living chains ends in a polyisoprene brush were first functionalized to yield hydroxy-terminated polyisoprene before formation of a poly(ethylene oxide) block. Successful functionalization was evidenced by both a change in water contact angles, from θ adv = 86 ± 2° for “grafting from” polyisoprene to θ adv = 47 ± 3° for “grafting from” hydroxy-terminated polyisoprene, and changes in the XPS carbon (1s) scans. The presence of a peak at 286.7 eV in the XPS carbon (1s) scan of the hydroxy-terminated polyisoprene was consistent with the presence of carbon bonded to alcohol groups. The hydroxy-terminated poly(isoprene) brush was converted to the corresponding potassium alkoxide with diphenylmethylpotassium and used to initiate ethylene oxide polymerization. Successful polymerization of the PEO block was substantiated by a reduction in the water contact angle (to θ adv = 35 ± 2°) and XPS carbon (1s) scans.