Fast and Reversible Cross-Linking Reactions of Thermoresponsive Polymers Based on Dynamic Dialkylaminodisulfide Exchange

Thermoresponsive polymers that can cross-link rapidly and reversibly under solvent-free conditions via the dynamic exchange of bis­(hindered amino)­disulfide (BiTEMPS) units have been prepared. Linear polymers with BiTEMPS units in their side chains were synthesized via free-radical copolymerization of hexyl methacrylate and a BiTEMPS-containing methacrylate monomer. When a polymer containing 5 mol % BiTEMPS was heated to 120 °C in the bulk, a cross-linked polymer was obtained within 10 min via exchange reactions of BiTEMPS units. The thermal cross-linking behavior of the linear polymer was investigated using in situ rheological measurements. Tensile tests indicated that the BiTEMPS-based small molecules generated during the cross-linking reaction acted as a plasticizer and enhanced the toughness of the polymer. A de-cross-linking reaction was also achieved under solvent-free conditions via an exchange reaction between the cross-linked polymer and a low-molecular-weight BiTEMPS derivative, which resulted in structural transformation to the original state. The structural transformation and the physical properties of the original linear polymer and the cross-linked polymers were characterized using gel permeation chromatography, rheology, tensile tests, and swelling experiments.