Direct Synthesis of Well-Defined Poly[{2-(methacryloyloxy)ethyl}trimethylammonium chloride] Brush via Surface-Initiated Atom Transfer Radical Polymerization in Fluoroalcohol

Abstract

A well-defined cationic polymer and polymer brush were simultaneously prepared by copper-catalyzed atom transfer radical polymerization (ATRP) of 2-(methacryloxy)ethyltrimethylammonium chloride (MTAC) in 2,2,2-trifluoroethanol (TFE) at 60 °C initiated with ethyl 2-bromoisobutylate and the corresponding alkylbromide immobilized on silicon wafer. ATRP of MTAC in TFE as well as aqueous solution proceeded quickly but in a poorly controlled manner, leading to a relatively higher molecular weight distribution (MWD) than Mw/Mn = 1.3, where Mw and Mn are weight-average and number-average molecular weights, respectively. Addition of a small amount of isopropyl alcohol to the TFE-based reaction mixture reduced the polymerization rate and produced a poly(MTAC) with predictable molecular weight and narrower MWD than 1.19. The Mn of poly(MTAC) was controllable in the range 104−105 g mol−1 based on the molar ratio of monomer and initiator in the feed. The Mn of the brush on a flat silicon wafer matched that of the free poly(MTAC). The graft density of poly(MTAC) was 0.20 chains nm−2. The ATRP of MTAC in TFE/1-ethyl-3-methylimidazolium chloride (EMImCl) also proceeded in a controlled manner at 60 °C, yielding polymers with narrow MWDs (Mw/Mn = 1.12−1.13). Analysis of the 13C NMR spectra of the carbonyl region of the resulting poly(MTAC)s revealed that syndiotactic-rich configurations were produced by ATRP of MTAC in aqueous solution, TFE/isopropyl alcohol, and TFE/EMImCl. The solvent effect of TFE and ionic liquid on the tacticity of polymer was negligible.