Jeffrey Pyun

Elemental sulfur has been used as a feedstock for polymer synthesis via the inverse vulcanization (IV) process. However, the role of molten sulfur itself as a high-temperature reactive processing medium for inorganic composite fabrication remains comparatively unexplored. Herein, we demonstrate that ultrahigh-purity sulfur (99.998%) functions simultaneously as a reactive monomer, transient dispersive medium, and processable precursor for the fabrication of highly filled inverse vulcanized glass (IVG)–molybdenum disulfide (IVG-MoS2) composites. Bulk micron-scale MoS2 particulates were incorporated at unusually high filler loadings (20–40 wt %) through iterative melt–mix–grind–remelt processing without requiring extensive nanosheet exfoliation, solvent-assisted processing, or surface functionalization. Subsequent inverse vulcanization with norbornadiene dimer (NBD2) afforded sulfur-rich glass composites exhibiting broad melt processability, centimeter-scale casting capability, and dynamic thermomechanical reprocessability arising from dense sulfur–sulfur covalent adaptability within the IVG covalent adaptable network (CAN). Mechanical characterization revealed systematic increases in flexural modulus and impact strength with increasing MoS2 incorporation, while the ability to reproducibly fabricate and notch specimens for standardized Izod impact testing highlights the unusual bulk coherence of these highly filled, sulfur-rich glass composites. Repeated hot-press reprocessing retained bulk mechanical integrity even in highly filled composites containing 20 wt % MoS2. Collectively, these findings establish homogeneous molten sulfur as an effective reactive processing medium for the fabrication of mechanically coherent, highly filled, and dynamically reprocessable sulfur-rich glass composites derived from inverse vulcanization.

Recent advances in sulfur polymer chemistry of elemental sulfur (S ₈ ) feedstocks have enabled the emergence of a new class of plastic optical glasses spanning applications from visible (VIS) wavelength photonics to long‐wave infrared (LWIR) imaging. In contrast to conventional optical polymers, S ₈ ‐derived polymers exhibit elevated refractive indices, broadband optical transparency, and favorable processing characteristics. This mini‐review summarizes recent developments in sulfur‐derived plastic optical glasses prepared through inverse vulcanization (IV) and sulfenyl chloride inverse vulcanization (SC‐IV) polymerizations. Inverse vulcanized glass (IVG) prepared from ultra‐high purity elemental sulfur afforded novel broadband VIS–LWIR plastic optics with high refractive index (RI, or n ≈ 1.9) and covalent adaptable network behavior. Extension of sulfur polymer chemistry to disulfide glass (DSG) materials derived from sulfur monochloride (S ₂ Cl ₂ ) enabled precision optical manufacturing of VIS‐IR transparent thermosets exhibiting reduced visible coloration, low optical attenuation, and compatibility with precision optics fabrication. Further development of photocurable disulfide methacrylate resin (DSMR) systems afforded a high refractive index photopolymer disulfide glass (Photo‐DSG) compatible with UV curing, microfabrication, and vat photopolymerization 3D printing workflows. These demonstrations establish sulfur‐derived polymers as a broader family of manufacturable plastic optical glasses bridging commodity sulfur feedstocks with emerging optical and photonic manufacturing technologies.

We report on the synthesis and self-assembly of thermally robust bottlebrush block copolymers (BBCPs) with enhanced pattern fidelity during high-temperature processing. The BBCPs were composed of glassy macromonomer side-chains of polystyrene (PS) and poly(methyl methacrylate) (PMMA) prepared via atom transfer radical polymerization (ATRP), followed by ring-opening metathesis polymerization (ROMP). Dehalogenation of PMMA and PS bromine terminated macromonomers was found to be the critical synthetic step to afford thermally stable BBCPs and phase-separated thin films. This subtle end-group modification was found to have dramatic consequences during the thermal processing of all-glassy segmented BBCPs, resulting in well-defined self-assembled morphologies. Atomic force microscopy and gel permeation chromatography with multiangle light scattering confirmed that the dehalogenated macromonomers and BBCPs exhibit excellent morphological stability. This strategy addresses a critical stability challenge in bottlebrush architectures and establishes a platform for defect-tolerant nanopatterning, advancing BBCPs toward practical applications in high-temperature directed self-assembly.

We review in this Viewpoint recent progress on the development of a new sustainable electrocatalytic system for water-splitting and molecular hydrogen generation using [diiron-disulfur] ([2Fe-2S]) active site methacrylate metallopolymers. To date, noble metal catalysts (e.g, platinum) remain the best electrocatalysts for molecular hydrogen generation using water as the chemical feedstock and proton donor. However, there remains a need for the synthesis of efficient electrocatalytic systems using low cost, earth abundant materials for sustainable H₂ generation. We focus on our recent work in this area using well-defined single site [2Fe-2S]-metallopolymer catalysts. Thus, far, these systems have demonstrated rates of hydrogen production >25 times faster than [FeFe]-hydrogenase enzymes and match the current densities of platinum with only 0.2 V higher potential when operating in water at neutral pH with tris(hydroxymethyl)aminoethane (TRIS) buffer (Faradaic yields 100 ± 3%). The molecular design and synthesis of [2Fe-2S]-metallopolymers are reviewed along with mechanistic studies unraveling the causality of efficient H₂ production from this catalytic system. The overall current output and overpotential are improved by the reversible electrostatic adsorption of the metallopolymer on the carbon electrode surface that enhances the proton and electron transfer rates and the use of protic buffer electrolytes (PBEs) that enhance the availability of protons. The schemes summarized here to improve the performance of [2Fe-2S] catalysts by incorporation into metallopolymers may be used to enhance the performance of other molecular electrocatalysts at the electrode surface.

A detailed understanding of the composition and polymerization mechanism of elemental sulfur remains a decades long unresolved question for modern chemistry. However, the dynamic nature of molten sulfur significantly complicates its accurate characterization. To overcome this challenge, we performed the first comprehensive molecular dynamics (MD) simulations using a ReaxFF reactive force field specifically parameterized to capture the complex ring‐opening polymerization dynamics of elemental sulfur. Rigorous development of the force field parameters, trained against extensive quantum mechanical datasets, was key to enabling these large‐scale (>10 000 atoms) reactive MD simulations at polymerization‐relevant temperatures. This study provides the first detailed atomic‐level description of liquid sulfur, elucidating temperature‐dependent molecular composition and offering unprecedented insights into sulfur polymerization mechanisms. These are the first simulations to reveal the formation of remarkably large macrocyclic sulfur rings at the onset of polymerization—a discovery that challenges longstanding mechanistic misconceptions, thus reshaping our understanding of sulfur polymerization. Our findings highlight the power of molecular dynamics in exploring complex polymerization processes, with broad impact in dynamic covalent chemistry and covalent adaptable polymers.

A detailed understanding of the composition and polymerization mechanism of elemental sulfur remains a decades long unresolved question for modern chemistry. However, the dynamic nature of molten sulfur significantly complicates its accurate characterization. To overcome this challenge, we performed the first comprehensive molecular dynamics (MD) simulations using a ReaxFF reactive force field specifically parameterized to capture the complex ring‐opening polymerization dynamics of elemental sulfur. Rigorous development of the force field parameters, trained against extensive quantum mechanical datasets, was key to enabling these large‐scale (>10 000 atoms) reactive MD simulations at polymerization‐relevant temperatures. This study provides the first detailed atomic‐level description of liquid sulfur, elucidating temperature‐dependent molecular composition and offering unprecedented insights into sulfur polymerization mechanisms. These are the first simulations to reveal the formation of remarkably large macrocyclic sulfur rings at the onset of polymerization—a discovery that challenges longstanding mechanistic misconceptions, thus reshaping our understanding of sulfur polymerization. Our findings highlight the power of molecular dynamics in exploring complex polymerization processes, with broad impact in dynamic covalent chemistry and covalent adaptable polymers.

The diverse functionalization of the polymeric support phase of diiron disulfide [2Fe-2S] metallopolymer electrocatalysts offers a route to the enhanced generation of molecular hydrogen via water-splitting. Click chemistry has been shown to be a useful tool in post-polymerization functionalization for a wide range of polymeric materials under mild conditions, which is a requirement for [2Fe-2S] metallopolymers due to the presence of iron carbonyl (Fe-CO) bonds in the active site. In this study, we developed a new synthetic methodology to functionalize [2Fe-2S] metallopolymers using atom transfer radical polymerization (ATRP) and post-polymerization functionalization using azide-alkyne "click" cycloaddition. Azide functional [2Fe-2S] metallopolymers were prepared by the ATRP of 3-azidopropyl methacrylate (AzPMA) with either methyl methacrylate (MMA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA), followed by copper-catalyzed "click" cycloaddition with functional terminal alkynes. Both families of PMMA and PDMAEMA functional [2Fe-2S] metallo-copolymers were found to retain Fe-CO bonds from the catalyst active site after the click chemistry reactions and, more importantly, exhibited high electrocatalytic activity for electrochemical water-splitting under pH-neutral aqueous conditions.

The development of a low‐cost photopolymer resin to fabricate optical glass of high refractive index for plastic optics is reported. This new free radically polymerizable photopolymer resin, termed, disulfide methacrylate resin (DSMR) is synthesized by the direct addition of allyl methacrylate to a commodity sulfur petrochemical, sulfur monochloride (S ₂ Cl ₂ ). The rapid rates of free radical photopolymerization confer significant advantages in preparing high‐quality, bulk optical glass. The low‐cost, optical glass produced from this photopolymer possesses a desirable combination of high refractive index ( n ≈ 1.57–1.59), low birefringence (Δ n < 10 ⁻⁴ ), high glass transition values ( T _g ≈ 100 °C), along with optical transparency rivaling, or exceeding that of poly(methyl methacrylate) (PMMA) as indicated by very low optical absorption coefficients ( α < 0.05 cm ⁻¹ at 1310 nm) measured for thick glass DSMR photopolymer samples (diameter ( D ) = 25 mm; thickness = 1–30 mm). The versatile manufacturability of DSMR photopolymers for both molding and diamond turn machining methods is demonstrated to prepare precision optics and nano‐micropatterned arrays. Finally, large‐scale 3D printing vat photopolymerization of DSMR using high‐area rapid printing digital light processing additive manufacturing is demonstrated.

The development of an organic optical glass, termed, disulfide glass (DSG), is reported as a new polymer for commodity plastic optics and thin film photonic applications. This low‐cost thermoset polymer possesses excellent transparency across the visible and infrared spectrum comparable to the best optical plastic to date, poly(methyl methacrylate), while having superior refractive index (n ≈ 1.6). DSG can be fabricated into defect‐free, thick optical glass by bulk addition polymerization of two commodity monomers (sulfur monochloride, 1,3,5‐triallyl isocyanurate) via a new polymerization, sulfenyl chloride inverse vulcanization. The robust mechanical properties and optical clarity of DSG enable fabrication of precision optics (lenses, prisms) via diamond turn machining to demonstrate the manufacturability of DSG for commodity plastic optics. Finally, the synthetic modularity of DSG is demonstrated to form solution processable forms for the fabrication of thin film polymer photonic devices, negative tone polymer photoresists, and micropatterned arrays.

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.