Water-Soluble Chiral Polyisocyanides Showing Thermoresponsive Behavior

To afford chiral polyisocyanides with thermoresponsiveness may open new gates to enhance their functionality and to broaden their applications. Herein, we report the synthesis of a series of novel polyisocyanides carrying oligoethylene glycols (OEGs) modified dipeptides as the pendent groups. These polyisocyanides not only show different chiroptical properties but also possess characteristic thermoresponsive behavior. The corresponding monomers carrying different OEG units in the periphery are water-soluble, thus allowing their polymerization feasible in aqueous medium with NiCl2 as the catalyst. For comparison, polyisocyanides were also prepared in organic solvents, such as dichloromethane and tetrahydrofuran. The effects of solvent and polymerization temperature as well as chemical structures of the pendants on the chiroptical properties of the resulting polymers were examined. The characteristic thermoresponsive behavior of these chiral polymers was investigated by H-1 NMR spectroscopy and turbidity measurements using UV/vis spectroscopy. The thermally induced aggregation processes were also followed by dynamic light scattering. It was found that the phase transition temperatures of these polymers were significantly influenced not only by the overall hydrophilicity but also by their secondary structures.