Boron-Rich Soft Hydrogels Based on the Coassembly of Cationic A‑B‑A Triblock Copolymers with Closo-Dodecaborate

We present an unusual type of electrostatic hydrogel based on anionic boron cluster compounds, which remain almost unexplored in the literature. Cationic PGEA-PEO-PGEA triblock copolymers coassembled with dianionic closo-dodecaborate clusters to nanostructures with the PGEA/closo-dodecaborate domains with a diameter of around 10-15 nm. Flower-like micelles were observed only at high dilutions, and the dynamic character of the domains was expressed by the formation of bigger particles consisting of multiple domains connected by the PEO bridges. The size of the nanogel particles gradually increased with the sample concentration, leading to macroscopic gelation of the solutions. The SAXS analysis revealed that the shape of the domains is also changing with sample concentration, and isolated short cylinders merge into a continuous phase in the gel-like samples. The rheology measurements showed that the length of the PGEA domain-forming blocks has a significant impact on the mechanical properties of the gels, and the increasing block length leads to stronger and more gel-like systems. All of the gels exhibit marked shear-thinning behavior, which extends over more than five decades of shear rates. Furthermore, the samples are largely self-healing but indicate certain structural reorganization of the network.