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 degrees 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.

Automated summary

Thermoresponsive polymers with rapid and reversible cross-linking under solvent-free conditions have been prepared via the dynamic exchange of Bis(hindered amino)disulfide (BiTEMPS) units. The cross-linking reaction through BiTEMPS units leads to enhanced toughness of the polymer, with the capability of structural transformation back to the original state. Various characterization techniques such as gel permeation chromatography, rheology, tensile tests, and swelling experiments were used to study the structural transformation and physical properties of the polymers.