Influence of the primary structure of the main chain on backbone stiffness of cylindrical rod brushes

The dimensional properties of rod brushes consisting of a flexible polymethacrylate main chain and poly( n -hexyl isocyanate; PHIC) rod side chains have been studied using static light and small-angle X-ray scattering (SAXS) techniques in tetrahydrofuran (THF) at 25 °C. The results are compared with those consisting of a flexible polystyrene main chain and PHIC side chains (VB-HIC- N s -H, where N s is the weight-averaged degree of polymerization of HIC). The rod brushes were prepared through the radical homopolymerizations of α-methacryloyloxyethoxy-ω-acetyl-PHIC macromonomer (MA-HIC- 61- Ac) in n -hexane at 60 °C. The molecular weight dependence of the z-averaged mean-square radius of gyration (〈 R g 2 〉 z ) of the brush is quantitatively described in terms of the wormlike cylinder model taking into account the end effects. The main chain stiffness parameter ( λ M −1 ) is determined to be 197 nm for poly(MA-HIC- 61- Ac), which is approximately three times greater than that for poly(VB-HIC- 62 -H), which has a polystyrene main chain and the same rod length. The considerably larger stiffness in the polymethacrylate than in the polystyrene is most likely responsible for the larger effective excluded volume effects produced by the freely rotating spacer between the main chain and side rod. A single rod brush of poly(MA-HIC- 61- Ac) on a mica surface is clearly observed using atomic force microscopy to reasonably demonstrate the cylindrical rod brushes. The influence of primary structure difference in the main chain on the dimensional properties of the cylindrical rod brush has been investigated by static light scattering and SAXS measurements to demonstrate that the backbone stiffness is greatly affected by the chemical nature of the main chain.