Palladium-based coordination cages as dynamic crosslinks in acrylamide hydrogels

Soft polymer networks with palladium cages as crosslinks can be obtained by combining polymeric N-donor ligands with PdII salts in organic solvents. Herein, we describe an alternative procedure that enables the preparation of hydrogels with PdnL2n-type junctions. The gels were obtained by photoinitiated copolymerization of palladium cages with acrylamide monomers in water. Cages with varying nuclearities (n = 2, 4, or 12) and different acrylates were employed. The material properties could be tuned by changing the crosslinker density. Thermoresponsive hydrogels were obtained when NIPAm was used as the monomer. The dynamic nature of the Pd-based crosslinks allows the creation of stimuli-responsive hydrogels. In particular, we were able to alter the network topology of a hydrogel by anion-induced conversion of Pd4L8 crosslinks into Pd2L4-type junctions.