Helix–Coil Transition in Cylindrical Brush Polymers with Poly-l-lysine Side Chains

Abstract

Cylindrical brush polymers with poly-l-lysine side chains were prepared by grafting lysine NCA from a macroinitiator via living ring-opening polymerization. The main chain degree of polymerization of the methacrylate main chain was Pw = 870, the side chains consisted of 25 and 55 lysine repeat units, respectively. Upon deprotection, the cylindrical brush polymers in 0.005 M NaBr exhibited an almost rodlike conformation with a Kuhn statistical segment length of several hundred nanometers. Cryo-TEM as well as AFM in aqueous solution clearly demonstrated pronounced undulations along the main chain at low ionic strength which could not be detected at higher salt concentrations. With increasing concentration of NaClO4 the PLL side chains underwent a coil-to-helix transition as revealed by CD measurements. The effect of the side chain coil-to-helix transition on the main chain stiffness could not be followed by light scattering due to intramolecular attraction (“folding”) of the cylindrical brushes at high salt...