1,2-Dithiolane-Derived Dynamic, Covalent Materials: Cooperative Self-Assembly and Reversible Cross-Linking

Area of Science:

• Polymer Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Dithiolane-containing polymers offer a route to dynamic and responsive materials.
• ABA triblock copolymers with poly(ethylene oxide) and polycarbonate blocks were synthesized.
• Pendant 1,2-dithiolane functionalities were incorporated into the polycarbonate blocks.

Purpose of the Study:

• To investigate the self-assembly and gelation behavior of dithiolane-functionalized ABA triblock copolymers.
• To elucidate the mechanism of thiol-induced ring-opening polymerization and cross-linking.
• To understand how dithiolane structure influences hydrogel properties.

Main Methods:

• Amphiphilic block copolymer synthesis and characterization.
• Small-angle X-ray scattering (SAXS) for micelle structure analysis.
• Rheological measurements to study gelation and mechanical properties.
• Kinetic and thermodynamic studies of dithiolane ring-opening polymerization.

Main Results:

• Amphiphilic block copolymers self-assemble into bridged flower micelles in aqueous solution.
• Addition of thiols triggers dithiolane ring-opening polymerization, leading to cross-linking and hydrogel formation.
• Hydrogels derived from methyl asparagusic acid exhibit dynamic, self-healing properties.
• Hydrogels derived from lipoic acid are rigid, resilient, and brittle.
• Dramatically different hydrogel properties correlate with the thermodynamics and kinetics of the specific dithiolane's ring-opening polymerization.

Conclusions:

• The structure of 1,2-dithiolane functionalities critically dictates the dynamic and mechanical properties of the resulting hydrogels.
• ABA triblock copolymers with dithiolane groups provide a versatile platform for designing tunable, responsive hydrogels.
• Incorporating different dithiolane monomers allows for precise control over hydrogel characteristics, from highly dynamic to rigid materials.