Water-soluble Chiral Polyisocyanides Showing Thermoresponsive Behavior

Stimuli-responsive polyisocyanides combine the unique properties of smartpolymers, the ordered secondary structure and high rigidity, which are promising inmany applications, including electronics, chiral catalysts and molecular devices.Though various stimuli-responsive polyisocyanides have been reported, lessattention was paid on thermoresponsive ones. Thermosponsive polymers are amongone of the most important stimuli-responsive polymers and found potentialapplications in the fields ranging from biomaterials, drug carriers to biosensors.Therefore, it’s valuable to develop novel polyisocyanides with attractive and tunablethermoresponsive properties.Herein, we report the synthesis of a series of novel polyisocyanides carryingoligoethylene glycols (OEGs) modified dipeptides as the pendent groups. Thesepolyisocyanides not only show different chiroptical properties, but also possesscharacteristic thermoresponsive property (Figure A). The corresponding monomerscarrying different OEG units in the periphery are water-soluble, thus allowing theirpolymerization feasible in aqueous medium with NiCl26H2O as the catalyst. Forcomparison, polyisocyanides were also prepared in organic solvents. The effects ofsolvent and polymerization temperature, as well as chemical structures of thependants on the chiroptical properties of the resulting polymers were examined. Thecharacteristic thermoresponsive behavior of these chiral polymers was investigatedby1H NMR spectroscopy and UV/Vis spectroscopy. The thermally-inducedaggregation processes were also followed by dynamic light scattering. It was foundthat the phase transition temperatures of these polymers were significantlyinfluenced not only by the over-all hydrophilicity but also by their secondarystructures.