Colorless High-Refractive-Index and X-ray-Shielding Polymer Films from m-Styrylbismuthines

Polymers containing heavy elements exhibit high refractive indices and excellent radiation shielding properties. However, a major challenge is their tendency to absorb visible light, leading to coloration and reduced transparency. To address this fundamental issue, we designed a bismuth-containing monomer that can undergo radical polymerization, in which the binding position of the polymerizable vinyl group was optimized, thereby introducing a novel molecular design that suppresses visible-light absorption. The resulting monomer underwent both thermal radical polymerization and photopolymerization, yielding a colorless, transparent, and self-supporting film that exhibited a high refractive index (n_D) of 1.72 and excellent X-ray shielding properties equivalent to 1.67 μm-Al/μm-polymer. This study establishes a new strategy for the molecular design of high-refractive-index transparent materials containing heavy elements and significantly expands their applications in optical and X-ray shielding materials.