Optical Properties of Photopolymerized Thiol–Ene Polymers Fabricated Using Various Multivinyl Monomers

Recent Progress in Sulfur-Containing High Refractive Index Polymers for Optical Applications

The development in the field of high refractive index materials is a crucial factor for the advancement of optical devices with advanced features such as image sensors, optical data storage, antireflective coatings, light-emitting diodes, and nanoimprinting. Sulfur plays an important role in high refractive index applications owing to its high molar refraction compared to carbon. Sulfur exists in multiple oxidation states and can exhibit various stable functional groups. Over the last few decades, sulfur-containing polymers have attracted much attention owing to their wide array of applications governed by the functional group of sulfur present in the polymer repeat unit. The interplay of refractive index and various other polymer properties contributes to successfully implementing a specific polymer material in optical applications. The focus on developing optoelectronic devices induced an ever-increasing need to integrate different functional materials to achieve the devices' full potential. Several devices that see the potential use of sulfur in high refractive index materials are reviewed in the study. Like sulfur, selenium also exhibits high molar refraction and unique chemical properties, making it an essential field of study. This review covers the research and development in the field of sulfur and selenium in different forms of functionality, focusing on the chemistry of bonding and the optical properties of the polymers containing the heteroatoms mentioned above. The strategy and rationale behind incorporating heteroatoms in a polymer matrix to produce high-refractive-index materials are also described in the present review.

UV-curable thiol-ene system for broadband infrared transparent objects

Conventional infrared transparent materials, including inorganic ceramic, glass, and sulfur-rich organic materials, are usually processed through thermal or mechanical progress. Here, we report a photo-curable liquid material based on a specially designed thiol-ene strategy, where the multithiols and divinyl oligomers were designed to contain only C, H, and S atoms. This approach ensures transparency in a wide range spectrum from visible light to mid-wave infrared (MWIR), and to long-wave infrared (LWIR). The refractive index, thermal properties, and mechanical properties of samples prepared by this thiol-ene resin were characterized. Objects transparent to LWIR and MWIR were fabricated by molding and two-photon 3D printing techniques. We demonstrated the potential of our material in a range of applications, including the fabrication of IR optics with high imaging resolution and the construction of micro-reactors for temperature monitoring. This UV-curable thiol-ene system provides a fast and convenient alternative for the fabrication of thin IR transparent objects.

UV-Induced Thiol-Ene "Click" Surface Grafting Polymerization on BOPP Substrate and Its Postmodifying for Hydrophilic and Antibacterial Applications

This paper proposed a novel and versatile surface modification route by integrating UV light-mediated thiol-ene "click" surface grafting polymerization and postmodification via the reactions of the surface thiol groups. At first, poly(thiol ether) layers with tunable thiol group density, up to 8.2 × 102 ea/nm3 for cross-linked grafting layers, were grafted from biaxially oriented polypropylene (BOPP) film. Then, the surface -SH groups reacted with epoxy compounds to introduce quaternary ammonium salt. With the immobilized quaternary ammonium salt and coordinated Zn2+ ions, the modified film demonstrated 99.98% antibacterial rate against Staphylococcus aureusafter soaking in DI water for 21 days and in a highly alkaline environment (0.1 M NaOH aqueous solution) for 3 days, and the surface water contact angle decreased to 39°. At last, the polymethacrylate chains were also successfully grafted from the surface thiol groups of the cross-linked poly(thiol ether) under visible light irradiation. With 2-(dimethyldodecylammonium) ethyl methacrylate as the grafting monomer, the modified BOPP film had shown a 99.99% antibacterial rate against both Escherichia coliand S. aureus. Meanwhile, with 2-methacryloxyethyl phosphoryl choline as grafting monomer, the modified surface showed an excellent antibioadhesion of living S. aureus, and the surface water contact angle was as low as 48°.

High Refractive Index Photopolymers by Thiol-Yne "Click" Polymerization

A scalable synthesis of high refractive index, optically transparent photopolymers from a family of low-viscosity multifunctional thiol and alkyne monomers via thiol-yne "click" is described herein. The monomers designed to incorporate high refractive index cores consisting of aryl and sulfide groups with high intrinsic molar refraction were synthesized starting from commercially available low-cost raw materials. The low-viscosity (<500 cP) thiol-yne resins formulated with these new multifunctional monomers and a phosphine oxide photoinitiator underwent efficient thiol-yne polymerizations upon exposure to 405 nm light at 30 mW/cm². In contrast to the previously reported thiol-ene systems, the kinetic profile of these photopolymerizations showed significant dependence on the nature of the thiol and alkyne monomers. However, the ability of the thiol-yne reaction to introduce a large number of sulfide linkages compared to that of thiol-ene systems yielded cross-linked high optical quality photopolymers with a polymer refractive index that exceeds 1.68 (n_D/20 °C). Interestingly, the photopolymer formed from the least sterically hindered alkynyl thioether monomer 2b with flexible thioether core and the dithiol 1a exhibited unprecedented difference in the polymer refractive index as compared to that of the resin with polymerization-induced changes reaching up to 0.08. Furthermore, the implementation of these low-viscosity thiol-yne resins was demonstrated by preparing two-stage photopolymeric holographic materials with a dynamic range of ∼0.02 and haze < 1.5% in two-dimensional high refractive index structures.