Synthesis of Water-Soluble Zwitterionic Polysiloxanes

A series of water-soluble siloxane polymers with pendent phosphorylcholine (PC) and sulfobetaine (SB) zwitterions was prepared using thiol-ene "click" chemistry. Specifically, well-defined vinyl-substituted siloxane homopolymers and block copolymers were functionalized with small molecule zwitterionic thiols at room temperature. Rapid and quantitative substitution of the pendent vinyl groups was achieved, and zwitterionic polysiloxanes of narrow molecular weight distribution were obtained. The PC-and SB-substituted polymers were found to be readily soluble in pure, salt-free water. Critical micelle concentrations (CMCs) of these polymers in water were measured using a pyrene fluorescence probe, with CMC values estimated to be <0.01 g/L. Polymer aggregates were studied by dynamic light scattering, and the micelles generated from the PC block copolymers were visualized, after drying, by transmission electron microscopy. Aqueous solutions of these zwitterionic polysiloxanes significantly reduced the oil-water interfacial surface tension, functioning as polymer amphiphiles that lend stability to oil-in-water emulsions. (C) 2015 Wiley Periodicals, Inc.