Green synthesis of well-defined linear poly(hydroxyl thioether) direct from epoxide in water

Abstract

Conventional synthetic routes to polythioether usually involve either high energy consumption or potential environmental and health impacts, often accomplished under rigorous conditions. Herein, the oxygen–sulfur exchange reaction (O–S ER) of epoxide and thiocyanate has been successfully combined with aqueous anionic ring-opening polymerization (AAROP) of the in situ generated episulfide, and an unprecedented approach referred to as “cascade O–S ER/AAROP” was established to obtain a well-defined hydroxyl-containing linear polythioether having high molecular weight of 58.6 kDa in an open system at 40 °C. Uniquely, thiocyanate can mediate the O–S ER of epoxide to supply an alkaline circumstance for enhancing the nucleophilicity of sulfanion, and also initiate AAROP of episulfide. The reaction mechanism is revealed by real-time monitoring of the reaction process and tracking pH value of aqueous medium, and further verified by capping and extending the living chain end. Organic ammonium salt can dramatically improve the yield and molecular weight of polythioether with narrow dispersity. This work presents a green strategy where AROP efficiently occurs in water, thereby paving a way to achieving linear poly(hydroxyl thioether) direct from epoxide under mild conditions.