Carborane-Containing Polymers as Advanced Materials

Abstract

Carboranes are electron-delocalized, icosahedral heteroborane clusters composed of 2 carbon and 10 boron atoms. Their σ-aromaticity, hydrophobicity, lipophilicity, and exceptional chemical, thermal, and metabolic stability make them attractive for use in fluorophores, heat-resistant materials, and biomedical fields. Their incorporation into polymer frameworks, beyond thermo-oxidation-resistant materials, has only emerged over the past 20 years. Modern controlled/living radical polymerization techniques remain rarely employed in the design of carborane-containing polymers with defined architectures. In this study, a closo-1,2-carborane-containing monomer was synthesized in high yield and polymerized via reversible addition-fragmentation chain-transfer (RAFT) polymerization. The reactions featured first-order kinetics and produced well-defined amphiphilic POEGMA-PCbEMA block copolymers. Their nanoparticles were prepared via polymerization-induced self-assembly (PISA) mediated by photoRAFT and photoinduced electron/energy transfer (PET)-RAFT polymerizations. While PET-RAFT-mediated PISA was largely uncontrolled, photoRAFT-mediated PISA produced spherical, interconnected/rod-like, and aggregated nanoparticles in an isopropyl alcohol–water mixture under green LED light, achieving efficient and controlled fabrication of carborane-containing nanomaterials. Strong host-guest interaction between closo-carboranes and β-cyclodextrin was utilized to design carborane-containing poly(methacrylic acid)-based hydrogels, which exhibited high mechanical strength, rapid self-healing, strong adhesion, and stretchability. The mechanical strength was influenced by carborane content, hydrogel concentration, and guest polymer molecular weight, while the rheological properties were found to depend primarily on the structure of the polymer. This work broadens the scope of carborane polymers, highlighting the potential of closo-1,2-carborane in polymer science and advanced material design.