Tunable Interpenetrating Polymer Network Hydrogels Based on Dynamic Covalent Bonds and Metal–Ligand Bonds

Abstract

A series of tunable interpenetrating polymer network (IPN) hydrogels are designed by the orthogonal incorporation of two distinct types of reversible bonds, i.e., Schiff base bonds and metal−ligand coordination bonds. Two copolymers based on poly(N,N-dimethyl acrylamide) (PDMA) are synthesized and used as building blocks for the IPN hydrogels. The first one bears ketone pendant groups and is cross-linked by dihydrazide or bishydroxylamine compounds to form, respectively, acylhydrazone-or oxime-based dynamic covalent bond (DCB) networks. The second one bears terpyridine side groups and is cross-linked by the addition of two different transition-metal cations to obtain supramolecular networks based on metal−terpyridine bis-complexes. Several IPN hydrogels are prepared by combining these different types of reversible bonds to investigate how the two subnetworks influence each other. To this end, the influence of the cross-linker nature and of the hydrogel preparation protocol on the rheological properties of these IPNs are also studied in detail. In particular, we show that the obtained IPN hydrogels exhibit a higher modulus compared to the simple addition of the moduli of the single networks, which we attribute to the entanglements between the two networks. We then study how these IPN hydrogels can disentangle and partially relax if one of the reversible subnetworks is composed of cross-links with a shorter lifetime. Finally, pH is used as a stimulus to affect the dynamics of only one of the subnetworks, and the impact of this change on the properties of the IPNs is investigated.

On the Validity of Effective Potentials in Crowded Solutions of Linear and Ring Polymers with Reversible Bonds

“…Having said this, there is plenty of evidence in the literature on formation of IPNs with purely reversible cross-links. [50][51][52][53][54] Our results suggests that such IPNs are kinetically trapped states. The typical activation energies of the dynamic bonds in these IPNs are of several hundreds of kJ/mol, 54 i.e., of the order of 100k B T whereas in our simulations they are about 10k B T .…”

Complementary Dynamic Chemistries for Multifunctional Polymeric Materials

“…Fustin and co‐workers [ 210 ] synthesized two copolymers based on poly( N , N ‐dimethyl acrylamide) to make an IPN hydrogels. Their first copolymer had ketone pendant groups and was crosslinked by dihydrazide or bishydroxylamine compounds to form acylhydrazone‐ or oxime‐based dynamic covalent networks.…”

Enhanced Mechanical Properties by Ionomeric Complexation in Interpenetrating Network Hydrogels of Hydrolyzed Poly (N-vinyl Formamide) and Polyacrylamide

“…The motivation for this work was the development of a high toughness hydrogel that did not derive its toughness from sacrificial covalent bonds as in double networks [ 22 ]. Toward this end, it was desirable to create a hydrogel that achieved high toughness using self-healing ionic bonds [ 38 ]. While hydrogels with two oppositely charged groups have been synthesized previously [ 5 , 11 , 15 , 32 , 35 , 38 ], here, the creation of such a hydrogel starting from two thermodynamically compatible neutral networks has been demonstrated.…”

“…Toward this end, it was desirable to create a hydrogel that achieved high toughness using self-healing ionic bonds [ 38 ]. While hydrogels with two oppositely charged groups have been synthesized previously [ 5 , 11 , 15 , 32 , 35 , 38 ], here, the creation of such a hydrogel starting from two thermodynamically compatible neutral networks has been demonstrated. In general, polyelectrolyte mixtures undergo a degree of microphase separation [ 21 , 22 ].…”