Advances in High-Refractive-Index Monomers Containing Unsaturated Groups

With the rapid and comprehensive development of research on high-refractive index materials and the demand for these materials in different fields, the structural design and application of the monomers containing unsaturated groups have been significantly explored, and the properties have improved in recent years. The structural design, polymerization method, optical properties, and application exploration of unsaturated double-bond high-refractive index monomers are analyzed in detail. Unsaturated high-refractive index monomers (UHRIMs) comprise high molar refractive index groups and unsaturated groups. In the structural design, the main types of unsaturated double bonds are vinyl (alkyne)/allyl, vinyl ether/allyl ether, (methyl)acrylate, cyclic olefin, maleimide, and others. The type of unsaturated group determines the polymerization method employed. The main polymerization methods include thiol-ene click reaction, thermal-initiated polymerization, photo-initiated polymerization, coordination polymerization, etc. In addition, the UHRIMs have relatively small molecular weight, high solubility, and mild molding conditions, which will have potential wide applications in nanoimprint, holographic technology, thermal infrared imaging, microlenses, optical devices, waveguide materials, coatings, etc.