Cylindrical Molecular Brushes with a Loose Grafting Density

A cylindrical molecular brush with a low graft density was synthesized by two steps. Firstly, free radical alternating copolymerization of styrene (St) and N-[2-(2-bromoisobutyryloxy)ethyl] maleimide (BiBEMI) gave a macroinitiator where pendant initiating sites for atom transfer radical polymerization (ATRP) being positioned along the backbone with an interval of four C-C bonds. The backbone-to-be with an alternating sequence was verified by elemental analysis (EA). Secondly, grafting poly(tert-butyl acrylate) chains from the macroinitiator by ATRP produced the novel molecular brush. Size exclusion chromatography, static light scattering (SLS), and H-1 NMR and atomic force microscopy (AFM) were used to characterize the macroinitiator and the molecular brush. The results show that the backbone contains an average 730 repeat units (1 repeat unit = a pair of St and BiBEMI) and the absolute molecular weight of the brush, M-w,M-sLS, was 4.88 x 10(6) Da. The brush reveals a number average length L-n to be 96 nm under AFM observation on carbon coated mica, corresponding to the length per main chain monomer unit (L-unit) of 0.066 nm, indicating a less extended conformation due to the low grafting density. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5527-5533, 2009