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

Abstract

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 1C. 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 a-methacryloyloxyethoxy-x-acetyl-PHIC macromonomer (MA-HIC-61-Ac) in n-hexane at 60 1C. The molecular weight dependence of the z-averaged mean-square radius of gyration (/R g 2 S 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 (k M À1) 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.

Graft Density Dependence of Main Chain Stiffness in Molecular Rod Brushes

“…24,25,28 The value of λ M −1 of the rod brushes linearly increased with the increasing of N s that followed the scaling law of λ M −1 ∝ N s 1 . The observed power law exponent value could not be explained by the theories for the rod brushes.…”

“…N s dependence of the measured ⟨S c 2 ⟩ 1/2 for PS-g-HIC-N s -0.22 samples and rod brushes from previous studies24,25,28 in THF at 25°C. The solid line is the theoretical value for semiflexible brush model calculated by eq 15 with l g = 0.22 nm.…”

Synthesis and properties of a rod-g-rod bottlebrush with a semirigid mesogen-jacketed polymer as the side chain

“…Scattering studies, including laser light scattering, 15,37,38 SAXS, 15,38,39 and small-angle neutron scattering (SANS), 37,[40][41][42] and AFM 23,43 are usually used to study the nanostructures of bottlebrushes. In order to study the sizes and shapes of the bottlebrushes, SAXS measurements were carried out on solutions of the bottlebrushes in THF at a concentration of 1 mg mL À1 at 25 C. As shown in Fig.…”

“…With the development of living and controlled polymerization and the "click" strategy, now there are mainly three ways to synthesize a bottlebrush: "graing onto", "graing through", and "graing from". [1][2][3][4] With these methods, different bottlebrushes with a exible backbone and exible side chains (coil-g-coil), 5,6 with a rigid backbone and exible side chains (rod-g-coil), [12][13][14] and with a exible backbone and rigid side chains (coil-g-rod) 15 have been synthesized. However, bottlebrushes with a rigid backbone and rigid side chains are rare 16 because it is difficult to synthesize rigid chains by controlled and living polymerization.…”

“…With a rigid backbone, the bottlebrush will be rigid even if the side chains are not so bulky; and with rigid side chains, the rigidity of the side chains will affect the main chain, making it stiffer. 15 Therefore, rod-g-rod bottlebrushes may have the advantage of forming ordered nanostructures with large dimensions, serving as potential candidates for nano-porous materials, photonic crystals, and so on.…”