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

Abstract

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_xPEG_yPU-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 PBA₅₀PEG₅₀PU-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 WPBA₉₀PEG₁₀PU-PS and WPBA₅₀PEG₅₀PU-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 WPBA₅₀PEG₅₀PU-PS/Gly₆₇ 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 WPBA₅₀PEG₅₀PU-PS/Gly₆₇/Na₁₀ 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 WPBA₅₀PEG₅₀PU-PS/Gly₆₇/Na₁₀ with additional antibacterial and sensing capabilities. This work provides a versatile approach for preparing transparent multifunctional hydrogels and highlights their potential in various applications.