High Refractive Index, Colorless Titanium Dioxide/Cyclic Olefin Polymer Composites via Designed Reactive Sites

High-refractive-index optical polymers are crucial for modern optoelectronic applications. Although cyclic olefin polymers exhibit numerous excellent optical properties, enhancing their refractive index remains a significant challenge. In this study, a series of cyclic olefin polymers with functional reactive sites was synthesized via ring-opening metathesis polymerization. These polymers were used to fabricate titanium dioxide/cyclic olefin polymer composites, which demonstrated excellent thermal stability and optical performance. TEM analysis revealed that the prepared TiO2 nanoparticles were uniformly sized and well-dispersed. AFM characterization revealed minimal phase separation and low surface roughness in the composite films. Upon incorporation of inorganic particles, the glass transition temperature of the composite material increased, reaching a maximum of 218.43 °C. The composites exhibited outstanding overall optical properties in the visible region, with optical transmittance exceeding 90% at 589 nm and a broadly tunable refractive index ranging from 1.543 to 1.734. Moreover, by controlling the nano TiO2 content, the surface wettability could be switched from hydrophobic (water contact angle ≈ 94.34°) to hydrophilic (water contact angle ≈ 46.48°). This work provides an approach for preparing high-refractive-index cyclic olefin polymers with potential optical applications.