Photocurable selenophene/maleimide-based high-refractive-index copolymers obtained via radical copolymerization

Diverse reactivity of maleimides in polymer science and beyond

Maleimides are remarkably versatile functional groups, capable of participating in homo- and copolymerizations, Diels-Alder and (photo)cycloadditions, Michael additions, and other reactions. Their reactivity has afforded materials ranging from polyimides with high upper service temperatures to hydrogels for regenerative medicine applications. Moreover, maleimides have proven to be an enabling chemistry for pharmaceutical development and bioconjugation via straightforward modification of cysteine residues. To exert spatiotemporal control over reactions with maleimides, multiple approaches have been developed to photocage nucleophiles, dienes, and dipoles. Additionally, further substitution of the maleimide alkene (e.g., mono- and di-halo-, thio-, amino-, and methyl-maleimides, among other substituents) confers tunable reactivity and dynamicity, as well as responsive mechanical and optical properties. In this mini-review, we highlight the diverse functionality of maleimides, underscoring their notable impact in polymer science. This moiety and related heterocycles will play an important role in future innovations in chemistry, biomedical, and materials research.

High-Refractive-Index Cross-Linked Cyclic Olefin Polymers with Excellent Transparency via Thiol-Ene Click Reaction

High-refractive-index polymers are important optical materials in optoelectronics. Conventional cyclic olefin polymers (COPs), possessing many excellent optical properties, are a class of highly promising optical materials; however, one of the greatest obstacles is their low refractive index of n = 1.52-1.54. Here, one efficient strategy of first incorporating high molar refraction groups, including carbazolyl and indolyl moieties, into unsaturated COPs via ring-opening metathesis polymerization (ROMP) and then introducing another high molar refraction sulfur atom by a subsequent thiol-ene click reaction is presented. The obtained cross-linked COPs bearing both an aromatic group and sulfur possess significantly higher refractive indices (n = 1.611-1.684 at 589 nm) and highly optical transparency (approximately 95%) in the range of vis-NIR. This provides a way toward potential applications of new-generation optical materials.

High Refractive Index Diphenyl Sulfide Photopolymers for Solar Cell Antireflection Coatings

The anti-reflection film can effectively reduce the surface reflectivity of solar photovoltaics, increase the transmittance of light, and improve the photoelectric conversion efficiency. The high refractive index coating is an important part of the anti-reflection film. However, the traditional metal oxide coating has poor stability and complicated processes. To address this issue, we prepared two organic high refractive index (HRI) photopolymers by modifying epoxy acrylic acid with 4,4′-thiodibenzenethiol, which can be surface patterned by nanoimprinting to prepare antireflection coatings. As a result, two modified photopolymers with high refractive index (n > 1.63), high optical transmittance (T > 95%), and thermal stability (Tg > 100 °C) are obtained after curing. In particular, the diphenyl sulfide photopolymer modified by ethyl isocyanate acrylate has a refractive index up to 1.667 cured by UV light. Our work confirms that the organic HRI photopolymer can be obtained by introducing high molar refractive index groups, with potential to be applied as a PV cell power conversion efficiency material.