Trapping Dynamic Disulfide Bonds in the Hard Segments of Thermoplastic Polyurethane Elastomers

Dynamic covalent bonds placed within a polymer chain result in stimulus-responsive materials where the breaking/making and/or exchange of the dynamic bonds controls the response. A key attribute to access such properties is the molecular mobility of the dynamic bonds. The focus of this work is to understand how incorporating a dynamic bond, in the form of disulfide bonds, into the hard phase of a polyurethane will impact the properties of the materials. Thus, uncross-linked polyurethanes with aliphatic disulfide-containing hard segments are synthesized via a two-step protocol, using 2,2'-dithiodiethanol and/or 1,4-butanediol in the second step as the chain extenders. Thermomechanical studies show that, if the dynamic bonds are selectively placed in the hard phase of the polyurethane, the dynamic nature of the disulfide bond can be effectively switched-off below the melting temperature of the hard phase. As such the dynamic and mechanical properties of the materials can be controlled by tailoring the nature of the hard phase.