Palladium-based coordination cages as dynamic crosslinks in acrylamide hydrogels

Abstract

Soft polymer networks with palladium cages as crosslinks can be obtained by combining polymeric N-donor ligands with Pd^II salts in organic solvents. Herein, we describe an alternative procedure that enables the preparation of hydrogels with Pd_nL_2n-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.