Polymer brushes with liquid crystalline side chains

We report on the synthesis and the properties of side-chain liquid-crystal polymer (LCP) brushes attached to silicon oxide surfaces. The polymer monolayers have been generated at the surface of the substrate in situ following a "grafting-from" procedure. The mesogenic group of the LC brushes consists of a phenylbenzoate moiety linked to the methacrylate main chain via a flexible spacer. The thickness of the brush and the grafting density of the surface-attached polymer molecules can be controlled by adjusting the monomer concentration during brush growth and the reaction time of the polymerization, respectively. LC brushes with a thickness of up to 200 nm in the dry, solvent-free state have been obtained. The transition temperatures between the nematic and the isotropic state have been studied and compared to those of spin-cast films of the same polymer. The optical textures are investigated as a function of layer thickness, temperature, and sample history. The textures exhibit a strong memory effect in the sense that the exact same texture reappears after isotropization by heating or solvent exposure and returning to the nematic state.