Mechanically robust hydrogel from thermosetting polybenzoxazine with dual crosslinking network

The main chain of polymer composition in hydrogels is mostly aliphatic and the crosslinking density is usually low, which renders the hydrogels with low mechanical strength. In this work, a kind of thermosetting resin, benzoxazine is used as the starting material to prepare the corresponding hydrogels by one-pot synthesis. The organic gels are firstly formed in dimethylformamide with the aid of catalyst, followed by extraction of water to give the hydrogels. It is revealed that due to the presence of covalent crosslinking and abundant hydrogen bonding, the as-prepared rigid hydrogels show extremely high compressive strength. The hydrogel with 55.8 wt % of water shows yield strength about 20 MPa and sustains compressive strength of 75 MPa (compressive stress of 30 kN, compressive strain of 67 %) without cracking. The hydrogel also show extremely high dielectric constant of 392,000, dielectric loss of 971,000, and ionic conductivity of 1.7 x 10-3 S/m at 100 Hz. Moreover, the responsiveness to pH variation suggests its potential application as smart responsive materials. To show the superiority of preparing functional composite hydrogels using this strategy, electroconductive and magnetic fillers are introduced and the as-prepared composite hydrogels show good electromagnetic shielding performance.