Nanoporous Bisphenol A-Based Polymeric Network Featuring Spontaneous Microphase-Separation Enables Transparent Multifunctional Hydrogels

Multifunctional hydrogels have garnered significant interest but remain challenging due to the complex preparation process and high cost of raw materials. Herein, bisphenol A diglycidyl ether (BADGE) and poly(ethylene glycol) diglycidyl ether (PEGDGE) were reacted with 3-amino-1-propanol via a catalyst-free amine–epoxy “click” chemistry, followed by the addition of hydrophilic 1,3-propane sultone (1,3-PS) to a higher water content, and then cross-linked with hexamethylene diisocyanate (HDI) in one-pot to provide a polymer network, i.e., PBA x PEG y PU–PS. The two-step cross-linking method enables greater precision in controlling the cross-linking density and preparation process. The in situ microphase-separated porous PBA 50 PEG 50 PU–PS demonstrates nanosized pores of approximately 100 nm and uniform distribution due to the thermodynamic incompatibility, enabling superior mechanical properties and high transparency of 87.9%. Upon a water absorption and water loss cycle, a higher transparency of 89.7% was obtained with a lower nanosized pore of approximately 50 nm due to the solvent-induced self-assembly of its amphiphilic structure. Furthermore, the bilayer hydrogel composed of WPBA 90 PEG 10 PU–PS and WPBA 50 PEG 50 PU–PS was designed for a “Janus” soft actuator based on the difference between the two sides in swelling ability upon water absorption, which has been applied in underwater grasping and humidity-responsive switch. To maintain the inherent soft elasticity and conductivity of the hydrogel, glycerol (Gly) and sodium ion (Na + ) were introduced into the mixture. It shows that WPBA 50 PEG 50 PU–PS/Gly 67 maintains environmental stability with more than 80% weight at 20 °C for 72 h and shows additional frost resistance at −20 °C, and the dual cross-linking network of WPBA 50 PEG 50 PU–PS/Gly 67 /Na 10 exhibits the best comprehensive properties of high tensile strength and good conductivity. Meanwhile, 1,3-PS provides a quaternary ammonium salt and sulfobetaine, endowing the multicomponent WPBA 50 PEG 50 PU–PS/Gly 67 /Na 10 with additional antibacterial and sensing capabilities. This work provides a versatile approach for preparing transparent multifunctional hydrogels and highlights their potential in various applications.