Dually cross-linked single networks: structures and applications

Abstract

Dually cross-linking endows polymeric materials with strength and responsiveness simultaneously. In this review, structural aspects of dually cross-linked single networks and possible applications are considered.

Enhancing Mechanical Performance of a Polymer Material by Incorporating Pillar[5]arene-Based Host–Guest Interactions

“…Due to this effective energy dissipation mechanism, polymer gels with physical crosslinkers can always bear a higher mechanical load, leading to outstanding toughness [ 12 ]. Apart from toughness, dual-crosslinked polymer gels are also capable of recovering their mechanical properties following relaxation, which is attributed to the cooperation of covalent crosslinking and the reversibility of non-covalent bonds [ 13 , 14 , 15 ]. Thus, incorporating physical crosslinkers in polymer gels is a promising strategy by which to improve the mechanical properties of polymer gels and has achieved much progress in numerous investigations [ 16 ].…”

“…To date, the most common physical crosslinkers include metal coordination [ 16 , 17 ], hydrogen bonds [ 18 , 19 , 20 ], and host–guest interactions [ 13 , 21 , 22 , 23 , 24 ]. Zhou et al utilized Fe 3+ –acrylic acid coordination as the crosslink point to design a dual-crosslinked hydrogel network that exhibits outstanding toughness and mechanical performance [ 25 ].…”

A hierarchical system of covalent and dual non-covalent crosslinks promotes the toughness and self-healing properties of polymer hydrogels

“…[6][7][8][9] The construction of noncovalent bonds has been gaining widespread attention for self-healing hydrogel materials, which is primarily based on metal-ligand, [10][11][12][13] host-guest, [14][15][16] hydrophobic, [17][18][19][20] hydrogen bonding, [21][22][23][24][25][26] and ionic interactions. [27][28][29] Generally, noncovalent bonds are more susceptible to the external environment than dynamic covalent linkages. The self-healing hydrogel systems based on non-covalent interactions are more stimuli-responsive and easier for structural control than those based on dynamically reversible covalent bonds.…”

Multi-energy dissipation mechanisms in supramolecular hydrogels with fast and slow relaxation modes

“…18 The characteristics of non-covalent bonds are often quantified by thermodynamics and dynamics. 21,29,32,33 These parameters complexly tune the properties of cross-linked supramolecular polymeric materials. In general, the thermodynamic parameter is related to the degree of cross-linking in the network.…”

“…Inspired by the different features of non-covalent bonds, combinations of several kinds of reversible cross-links in a single network have attracted much attention as a way to establish more highly functional materials. 32 Such hydrogels containing two kinds of reversible cross-links are called dual physically cross-linked hydrogels. While many of them were designed for effective self-healing [34][35][36][37] and multistimuli responsiveness, [38][39][40][41][42][43][44] some hydrogels cross-linked by metal-ligand coordination, 33,45 hydrogen bonding, 46,47 or ionic interactions 48,49 have exhibited outstanding mechanical properties, probably due to their high binding energies.…”