Fast Gelation and Mechanical Reinforcement of Tetrahydroxydiboron-Induced Free Radical Polymerized Hydrogels under Harsh Conditions

Abstract

Hydrogels prepared through free radical polymerization hold great promise for large-scale production and practical applications but face challenges due to oxygen inhibition during polymerization and poor mechanical properties. These issues often necessitate complex structural designs and time-consuming anaerobic processes. This work presents a novel approach using tetrahydroxydiboron (THDB) combined with potassium persulfate (KPS) to rapidly produce hydrogels with enhanced mechanical properties under aerobic conditions, overcoming traditional limitations. The THDB-KPS system facilitates the gelation of acrylamide (AM) precursors in just 2 min under ambient conditions, significantly outperforming existing systems. This method is versatile across various monomer types, including hydrophilic, electrolyte, macromolecular and zwitterionic monomers. This rapid gelation effect stems from the THDB’s ability to interact with dissolved oxygen to neutralize the inhibitory effects of oxygen, and to promote persulfate decomposition efficiently by homolytic cleavage to produce (HO)₂B· radicals through the coordination of N or O in the vinyl monomers with the diboron structure. Meanwhile, boron-induced hydrogen bonding and coordination interactions, along with the fast rise in temperature and viscosity of the reaction system, contribute to the shortened gelation time as well. These factors also lead to the formation of multiple physical cross-links as well as a network of densely and loosely cross-linked regions. Consequently, the mechanical properties of the hydrogel are significantly enhanced through the progressive deformation of these densely and loosely cross-linked regions along with the breakage of physical cross-links. This rapid gelation and mechanical reinforcement effect remains effective even under challenging conditions, including acidic or alkaline environments, low temperatures and impurity-laden environments. Therefore, this breakthrough offers a scalable and efficient method for producing high-performance hydrogel under harsh conditions, promising substantial advancements in industrial applications and practical use in diverse fields.