Long-wave infrared transparent sulfur polymers enabled by symmetric thiol cross-linker

A Thermally Stable, Infrared-Transparent High-Sulfur-Containing Polymer for High Aspect-Ratio Nanostructured MWIR Polarizer

Infrared (IR) polarizer is essential for thermal imaging applications such as mobility and military operations. High-sulfur-containing polymers have emerged as promising candidates for IR polarizers due to their mid-wave IR (MWIR) transparency, addressing the limitations of inorganic materials, including their brittleness and high cost. However, poor thermal stability and limited IR range restrict their applicability. This study introduces a glassy IR polarizer based on poly(sulfur-co-hexavinyl disiloxane) (pSHVDS), a highly crosslinked sulfur-rich polymer synthesized via sulfur chemical vapor deposition (sCVD). Self-crosslinking of pSHVDS at high temperatures provided thermal stability during nanoimprint lithography, enabling the fabrication of high-fidelity nano-grating patterns (400 nm pitch, 150 nm width, 300 nm height). The broad transmittance and high aspect ratio of the nanopattern enabled the glassy-pSHVDS MWIR polarizer to achieve over 50% transmittance of transverse magnetic field (TTM) and an extinction ratio (ER) exceeding 6000 across a broad IR range (3-8 µm). An additional pSHVDS anti-reflection coating further enhanced TTM to 84% and ER to 7200 at a wavelength of 4 µm, the highest ER reported for organic MWIR polarizers to date. The polarizer maintained its performance after 24 h at 100 °C, demonstrating exceptional thermal stability. These findings underscore the potential of glassy pSHVDS-based polarizers for IR applications.

Inverse Vulcanization-Induced Self-assembly of Polysulfide into Responsive Micelles and their Templated Hydrogel Adsorbent for Sr2+ Removal

Albeit sulfur-rich polymers have attracted increasing attention and become easily accessible, especially after the emergence of inverse vulcanization, a myriad of polysulfides suffer from limited water solubility due to the hydrophobic nature of sulfur and comonomers, hindering their use in water-related fields (e.g., metal remediation). Inverse vulcanization of water-soluble monomers still remains limited, let alone the understanding of its reaction mechanism in water and of its solution properties. In this study, sodium acrylate was employed to copolymerize with elemental sulfur in water to synthesize ionic polysulfides (SSAC) using organic bases as catalysts. A mechanism involving nucleophilic attack initiation, carbanion propagation, and water-involved hydrolysis termination is reported for the formation of SSACs with molecular weights of 1.1 to 1.7 kDa. There also exists possible side reactions of sulfur hydrolysis in alkaline water that produced sulfur oxoacid and its salts as byproducts. The ionic SSAC was demonstrated to be superhydrophilic and, more importantly, identified to self-assemble into stable negatively charged colloids with a hydrodynamic size of ∼130 nm and a critical micellar concentration of ∼10 mg/L. Then, the SSAC micelles were templated into a homogeneous sulfur-rich hydrogel (SSAC hydrogel) as physical cross-links via an ion-imprinting technique aided by sodium alginate. The hydrogel exhibits self-healing ability and outstanding adsorption capability to Sr2+ with a qm of 134.4 mg/g and good robustness in a wide range of temperature (25 to 55 °C) and pH (4 to 10). Also, fast adsorption kinetics and good selectivity in the presence of Ca2+, Mg2+, and K+ with high concentrations were demonstrated.

Redox-activatable inhalable mucoadhesive proteinic nanotherapeutics for targeted treatment of lung cancer

Inhalation delivery has been considered a promising choice for treating lung cancer because it can shuttle therapeutic payloads directly to cancer tissues via simple and noninvasive procedures while reducing systemic toxicity. However, its clinical application still faces challenges, especially for delivering hydrophobic chemotherapeutic drugs, due to poor absorption on mucosal tissues and limited therapeutic performance. Herein, we propose inhalable mucoadhesive proteinic nanoparticles (NPs) capable of facilitating reliable pulmonary drug delivery and redox-responsive anticancer therapeutic effects to realize noninvasive, localized treatment of lung cancer in a highly biocompatible, site-specific manner. Thiolated mussel adhesive protein (MAP)-based NPs (thMAP NPs) can be administered to target tissues via an easy and facile nebulization process due to their superior MAP-driven adhesion ability and sufficient structural integrity. Curcumin (Cur)-loaded thMAP NPs (thMAP@Cur NPs) demonstrated efficient cellular uptake through the thiol-mediated pathway and controlled the intracellular release of Cur in response to the reductive environment in cancer cells. The nebulized thMAP@Cur NPs elicited prolonged retention in lung tissue without causing any detectable adverse effects, leading to significant inhibition of metastatic lung cancer in vivo. Thus, these protein-based redox-responsive mucoadhesive NPs hold great promise as robust inhalable drug delivery platforms to achieve effective, localized treatment of pulmonary cancer and other respiratory diseases.

Adding Value into Elementary Sulfur for Sustainable Materials

Sulfur-rich copolymers, characterized by high sulfur contents and dynamic disulfide bonds, show significant promise as sustainable alternatives to conventional carbon-based plastics. Since the advent of inverse vulcanization in 2013, numerous synthesis strategies have emerged - ranging from thermopolymerization and photoinduced polymerization to the use of crosslinkers such as mercaptans, episulfides, benzoxazines, and cyclic disulfides. These advancements coupled with the rising demand for degradable plastics have driven research for diverse applications, including optical windows, metal uptake, and adhesives. Due to the unique electronic properties of sulfur-rich materials, they are promising candidates for cathodes in Li-S batteries and triboelectric nanogenerators. This review highlight the latest exciting ways of synthesis strategy in which sulfur and sulfur-based reactions are bing utilized to produce sustainable materials in energy, optics, engeneering material, environemtal, and triboelectric nanogenerators. Finally, this review provides a forward-looking perspective on the opportunities and challenges shaping this rapidly evolving field.

Dynamic Covalent Sulfur-Selenium Rich Polymers via Inverse Vulcanization for High Refractive Index, High Transmittance, and UV Shielding Materials

Recent advancements in inverse vulcanization have led to the development of sulfur-rich polymers with diverse applications. However, progress is constrained by the harsh high-temperature reaction conditions, limited applicability, and the generation of hazardous H2S gas. This study presents an induced IV method utilizing selenium octanoic acid, yielding sulfur-selenium rich polymers with full atom economy, even at a low-temperatures of 100-120 °C. The resultant sulfur-selenium rich polymers exhibit exceptional optical properties: 1) A high refractive index, reaching 1.89 when the total sulfur-selenium content is 65%; 2) Excellent UV shielding capabilities, blocking ultraviolet rays while permitting 95.1-98.6% transmission of visible light; 3) Notable transparency, with polymer films of 0.94 mm thickness exhibiting good transparency under natural light. The materials also demonstrate environmental stability under prolonged exposure to hot or cold conditions. Additionally, the polymers display adhesive strength as evidenced by two adhered glass slides with the material lifting weights of up to 20 kg without any displacement in their glued area. These properties provide a new avenue for sulfur-selenium rich materials to be implemented in high-precision optical instruments with unique characteristics.

Electromagnetic Interference (EMI) Shielding Performance and Photoelectric Characteristics of ZnS Infrared Window

ZnS material shows great application prospects in fields such as infrared windows, fairings, and lenses. In this study, a crack template method was developed to prepare gold meshes with random structures on ZnS optical window. The crack template and gold meshes structures were designed from a completely new perspective focusing on the period and line width ratio. Then, four different structural parameters of the gold mesh were fabricated using the crack template method, their ratios of the aperture to line width were 16.1, 17.4, 18.0, and 19.0. The templates' morphology and structural traits were examined via optical and laser confocal microscopy. The sample with a ratio of aperture to line width of 16.0 had the best connectivity and the highest coverage, at 15.33%, while the sample with a ratio of aperture to line width of 19.0 had the lowest coverage, at 11.64%. Gold meshes were deposited using these templates, where an increase in the aperture-to-line width ratio resulted in average transmittances of 57.1% and 63.2% over the 2-10 μm range. The electromagnetic shielding efficiency surpassed 22.5 dB within the 1-18 GHz range, while the 1#-mesh, with an aperture-to-line width ratio of 16.0, achieved 33.2 dB at 1 GHz. This research endeavor contributes significantly to advancing the understanding of the ZnS glass' optoelectric performance and enhances their potential for practical applications.

Sulfur-Rich Norbornadiene-Derived Infrared Transparent Polymers by Inverse Vulcanization

Infrared (IR) transparent polymer materials prepared by inverse vulcanization, as a promising candidate to replace inorganic materials, are new materials for constructing key devices in IR optics. However, it is difficult to achieve a balance between infrared optical and thermal properties in polymers due to the intrinsic infrared absorption of organic materials. Herein, our strategy is to construct a high boiling point symmetrical molecular norbornadiene derivative cross-linking agent (DMMD) which can be inverse vulcanized with molten sulfur, and obtain Poly (S-r-DMMD) with different sulfur content by controlling the feed ratio of sulfur. With the rigid core and low IR activity in DMMD, the prepared polymers exhibit tunable thermal properties (Tg: 98.3-119.8 °C) and high IR transmittance (medium-wave infrared region (MWIR): 42.9-52.6 %; long-wave infrared region (LWIR): 1.5-5.29 %). In addition, Poly (S-r-DMMD) can be used to prepare large-size free-standing Fresnel lenses for IR imaging by simple hot-pressing, which provides flexibility in the design and production of IR fine lenses. This study provides a novel strategy for balancing the thermal and optical properties of IR transparent polymer materials, while providing relevant references for balancing the IR optical and thermal properties of polymer materials.

Sodium Thiophenolate Initiated Polymerization of Methacrylate with Sulfur (S8): High-Refractive-Index and -Transparency Polymers for Lithography

A simple and effective strategy for introducing sulfur into a polymethacrylate matrix at room temperature has been developed, allowing for the polymerization of a variety of methacrylate derivatives with sulfur. The resulting S-containing polymers exhibited a high refractive index of up to 1.72 while retaining over 90% transmittance in the visible region. Additionally, when mixed with 3% photo acid generator (PAG) as photoresist, the formulation demonstrated excellent patterning capabilities. Furthermore, the scalable preparation of high-refractive-index polymers (HRIPs) indicates significant potential for fabrication.

Transforming Element Sulfur to High Performance Closed-Loop Recyclable Polymer via Proton Transfer Enabled Anionic Hybrid Copolymerization

The utilization of sulfur has been a global issue. Copolymerization of element sulfur (S8) with other monomers is a promising route to convert it to useful materials but is limited by the comonomers. Here, we report anionic hybrid copolymerization of S8 with acrylate and epoxide at room temperature, where S8 does not copolymerize with epoxide in the absence of acrylate. Yet, the proton transfer from the methyne in acrylate to the oxygen anion enables the ring-opening of the cyclic comonomer and hence the copolymerization. The cyclic comonomers can be expanded to lactone and cyclic carbonate. Specifically, the copolymer of S8 with bisphenl A diglycidyl ether and diacrylate displays mechanical properties comparable to those of most common plastics, namely, it has ultimate tensile strength as high as 60.8 MPa and Young's modulus up to 680 MPa. It also exhibits high UV resistance and good transparency. Particularly, it has excellent UV-induced self-healing, reprocessability and closed-loop recyclability due to the abundant dynamic S-S bonds and ester groups. This study provides an efficient strategy to turn element sulfur into closed-loop recyclable polymer with high mechanical and optical performances.

Prediction of the Infrared Absorbance Intensities and Frequencies of Hydrocarbons: A Message Passing Neural Network Approach

Accurately and efficiently predicting the infrared (IR) spectra of a molecule can provide insights into the structure-properties relationships of molecular species, which has led to a proliferation of machine learning tools designed for this purpose. However, earlier studies have focused primarily on obtaining normalized IR spectra, which limits their potential for a comprehensive analysis of molecular behavior in the IR range. For instance, to fully understand and predict the optical properties, such as the transparency characteristics, it is necessary to predict the molar absorptivity IR spectra instead. Here, we propose a graph-based communicative message passing neural network algorithm that can predict both the peak positions and absolute intensities corresponding to density functional theory calculated molar absorptivities in the IR domain. By modifying existing spectral loss functions, we show that our method is able to predict with DFT-accuracy level the IR molar absorptivities of a series of hydrocarbons containing up to ten carbon atoms and apply the model to a set of larger molecules. We also compare the predicted spectra with those generated by the direct message passing neural network. The results suggest that both algorithms demonstrate similar predictive capabilities for hydrocarbons, indicating that either model could be effectively used in future research on spectral prediction for such systems.

Ultrathin near-infrared transmitting films enabled by deprotonation-induced intramolecular charge transfer of a dopant

Near-infrared transparent films demonstrate important applications in many fields, but how to eliminate light interference from ultraviolet-visible region and how to tackle the trade-off effect between film thickness and transmittance remain as challenges. Herein, we report a near-infrared transparent film that achieves high-efficient combination of thin thickness (16 μm), suitable cut-off wavelength (890 nm), and ideal transmittance (TNIR > 90%, TVis < 1%). Moreover, the film is photo-chemically stable, heating resistance and moisture insensitive. The key component of the film is a complex of a specially designed boron compound containing a perylene monoimide unit (PMI-CBN) with an organic base 1,8-diazabicyclo[5,4,0]undec-7-ene. The complex depicts red-shifted absorption from 709 to 943 nm owing to deprotonation of the N-H group of PMI-CBN. Dispersion of the complex in polymethyl methacrylate results in the high-performance film. As demos, the film is successfully used for night vision imaging and information encryption.

Synthesis of Polycyclic Olefinic Monomers from Norbornadiene for Inverse Vulcanization: Structural and Mechanistic Consequences

The preparation of high-sulfur content organosulfur polymers has generated considerable interest as an emerging area in polymer science that has been driven by advances in the inverse vulcanization polymerization of elemental sulfur with organic comonomers. While numerous new inverse vulcanized polysulfides have been made over the past decade, insights into the mechanism of inverse vulcanization and structural characterization of the high-sulfur-content copolymers remain limited in scope. Furthermore, the exploration of new molecular architectures for organic comonomer synthesis remains an important frontier to enhance the properties of these new polymeric materials. In the current report, the first detailed study on the synthesis and inverse vulcanization of polycyclic rigid comonomers derived from norbornadiene was conducted, affording a quantitative assessment of polymer microstructure for these organopolysulfides and insights into the inverse vulcanization polymerization mechanism for this class of monomers. In particular, a stereoselective synthesis of the endo-exo norbornadiene cyclopentadiene adduct (Stillene) was achieved, which enabled direct comparison with the known exo-exo norbornadiene dimer (NBD2) previously used for inverse vulcanization. Reductive degradation of these sulfur copolymers and detailed structural analysis of the recovered sulfurated organic fragments revealed that remarkable exo-stereospecificity was achieved in the inverse vulcanization of elemental sulfur with both these polycyclic dienyl comonomers, which correlated to the robust thermomechanical properties associated with organopolysulfides made from NBD2 previously. Melt processing and molding of these sulfur copolymers were conducted to fabricate free-standing plastic lenses for long-wave infrared thermal imaging.

Converting inorganic sulfur into degradable thermoplastics and adhesives by copolymerization with cyclic disulfides

Converting elementary sulfur into sulfur-rich polymers provides a sustainable strategy to replace fossil-fuel-based plastics. However, the low ring strain of eight-membered rings, i.e., S8 monomers, compromises their ring-opening polymerization (ROP) due to lack of an enthalpic driving force and as a consequence, poly(sulfur) is inherently unstable. Here we report that copolymerization with cyclic disulfides, e.g., 1,2-dithiolanes, can enable a simple and energy-saving way to convert elementary sulfur into sulfur-rich thermoplastics. The key strategy is to combine two types of ROP-both mediated by disulfide bond exchange-to tackle the thermodynamic instability of poly(sulfur). Meanwhile, the readily modifiable sidechain of the cyclic disulfides provides chemical space to engineer the mechanical properties and dynamic functions over a large range, e.g., self-repairing ability and degradability. Thus, this simple and robust system is expected to be a starting point for the organic transformation of inorganic sulfur toward sulfur-rich functional and green plastics.

Heteroatom-facilitated blue to near-infrared emission of nonconjugated polyesters

Making nonconjugated polymers to emit visible light remains a formidable challenge, let alone near-infrared (NIR) light, although NIR luminophores have many advanced applications. Herein, we propose an electron-bridging strategy of using heteroatoms (O, N, and S) to achieve tunable emission from blue to NIR regions (440-800 nm) in nonconjugated polyesters. Especially, sulfur-containing polyester P4 exhibits NIR clusteroluminescence (CL) on changing either the concentration or excitation wavelength. Experimental characterization and theoretical calculation demonstrate that the introduction of heteroatoms significantly enhances the through-space interactions (TSIs) via the electron-bridging effect between heteroatoms and carbonyls. The strength of the electron-bridging effect follows the order of S > N > O, based on two synergistic effects: electronic structure and van der Waals radius of heteroatoms. This work provides a low-cost, scalable platform to produce new-generation nonconjugated luminophores with deeper insight into the photophysical mechanism.

Synthesis of Deuterated and Sulfurated Polymers by Inverse Vulcanization: Engineering Infrared Transparency via Deuteration

The synthesis of deuterated, sulfurated, proton-free, glassy polymers offers a route to optical polymers for infrared (IR) optics, specifically for midwave IR (MWIR) photonic devices. Deuterated polymers have been utilized to enhance neutron cross-sectional contrast with proteo polymers for morphological neutron scattering measurements but have found limited utility for other applications. We report the synthesis of perdeuterated d14-(1,3-diisopropenylbenzene) with over 99% levels of deuteration and the preparation of proton-free, perdeuterated poly(sulfur-random-d14-(1,3-diisopropenylbenzene)) (poly(S-r-d14-DIB)) via inverse vulcanization with elemental sulfur. Detailed structural analysis and quantum computational calculations of these reactions demonstrate significant kinetic isotope effects, which alter mechanistic pathways to form different copolymer microstructures for deutero vs proteo poly(S-r-DIB). This design also allows for molecular engineering of MWIR transparency by shifting C-H bond vibrations around 3.3 μm/3000 cm-1 observed in proteo poly(S-r-DIB) to 4.2 μm/2200 cm-1. Furthermore, the fabrication of thin-film MWIR optical gratings made from molding of deuterated-sulfurated, proton-free poly(S-r-d14-DIB) is demonstrated; operation of these gratings at 3.39 μm is achieved successfully, while the proteo poly(S-r-DIB) gratings are opaque at these wavelengths, highlighting the promise of MWIR sensors and compact spectrometers from these materials.

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.