Ultra-stiff and tough hydrogels based on small but strong hydrophobic associations via a low-reactive hydrophilic monomer

Synthetic hydrogels have achieved great progress in mechanical performance. But it is still a challenge to combine adequate stiffness, strength, and toughness in a single hydrogel. Herein, ultra-stiff, strong, and tough hydrogels are prepared by constructing a network with dense, small but strong hydrophobic associations. A hydrophobic monomer, 2-aminoethyl methacrylate isopropyl carbamate (IMA), is used to form strong hydrophobic associations enhanced by hydrogen bonding due to its hydrophobic moiety-protected carbamate side group. Low-reactive hydrophilic acrylamide (AAm) is copolymered with IMA at different monomer ratios to tailor the density, size, and strength of hydrophobic associations. Finally, a homogeneous and compact network based on dense but small and strong hydrophobic associations is constructed, and the hydrogels show comprehensive mechanical performance with the compressive modulus ranging from 28 to 200 MPa, compressive stress (85% strain) > 100 MPa, and compressive toughness from 9 to 26 MJ m(-3). These hydrogels also display good self-recovery and fatigue resistance due to these dynamic cross-links. These ultra-stiff, strong, and tough hydrogels show great potential as load-bearing materials in many fields.