Palladium-based coordination cages as dynamic crosslinks in acrylamide hydrogels

Area of Science:

• Materials Science
• Polymer Chemistry
• Supramolecular Chemistry

Background:

• Soft polymer networks are typically formed using covalent crosslinks.
• Palladium (Pd) complexes offer dynamic coordination chemistry suitable for creating reversible crosslinks.

Purpose of the Study:

• To develop a water-based method for creating hydrogels crosslinked by palladium cages.
• To investigate the tunability and stimuli-responsive properties of these novel hydrogel materials.

Main Methods:

• Photoinitiated copolymerization of palladium cages with acrylamide monomers in aqueous solution.
• Utilized palladium cages with varying nuclearities (n=2, 4, or 12) and different acrylates.
• Incorporated N-isopropylacrylamide (NIPAm) to achieve thermoresponsive properties.

Main Results:

• Successfully synthesized hydrogels with Pd₂L₄-type junctions via photoinitiation in water.
• Demonstrated that material properties, such as crosslinker density, can be tuned.
• Achieved stimuli-responsive hydrogels, including thermoresponsive behavior with NIPAm.
• Showcased anion-induced conversion of Pd₄L₈ to Pd₂L₄ crosslinks, altering network topology.

Conclusions:

• Photoinitiated copolymerization in water provides an efficient route to palladium-cage-crosslinked hydrogels.
• The dynamic nature of palladium crosslinks enables the design of tunable and stimuli-responsive soft materials.
• Anion-responsive network transformations highlight the potential for advanced material design.