Polymerizations with Elemental Sulfur: From Petroleum Refining to Polymeric Materials

Thermally Stable and Chemically Recyclable Poly(ketal-ester)s Regulated by Floor Temperature

Chemical recycling to monomers (CRM) offers a promising closed-loop approach to transition from current linear plastic economy toward a more sustainable circular paradigm. Typically, this approach has focused on modulating the ceiling temperature (Tc) of monomers. Despite considerable advancements, polymers with low Tc often face challenges such as inadequate thermal stability, exemplified by poly(γ-butyrolactone) (PGBL) with a decomposition temperature of ∼200 °C. In contrast, floor temperature (Tf)-regulated polymers, particularly those synthesized via the ring-opening polymerization (ROP) of macrolactones, inherently exhibit enhanced thermodynamic stability as the temperature increases. However, the development of those Tf regulated chemically recyclable polymers remains relatively underexplored. In this context, by judicious design and efficient synthesis of a biobased macrocyclic diester monomer (HOD), we developed a type of Tf -regulated closed-loop chemically recyclable poly(ketal-ester) (PHOD). First, the entropy-driven ROP of HOD generated high-molar mass PHOD with exceptional thermal stability with a Td,5% reaching up to 353 °C. Notably, it maintains a high Td,5% of 345 °C even without removing the polymerization catalyst. This contrasts markedly with PGBL, which spontaneously depolymerizes back to the monomer above its Tc in the presence of catalyst. Second, PHOD displays outstanding closed-loop chemical recyclability at room temperature within just 1 min with tBuOK. Finally, copolymerization of pentadecanolide (PDL) with HOD generated high-performance copolymers (PHOD-co-PPDL) with tunable mechanical properties and chemical recyclability of both components.

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.

Improved access to polythioesters by heterobimetallic aluminium catalysis

Bimetallic Al(III) catalysis mediates thioanhydride/epoxide copolymerisation at greatly improved rates and monomer tolerance than analogous Cr(III) catalysis. Moving to sulfurated monomers furthermore generally improves rates and selectivites.

Size Control and Antioxidant Properties of Sulfur-Rich Polymer Colloids from Interfacial Polymerization

High sulfur content polymeric materials, known for their intriguing properties such as high refractive indices and high electrochemical capacities, have garnered significant interest in recent years for their applications in optics, antifouling surfaces, triboelectrics, and electrochemistry. Despite the high interest, most high sulfur-content polymers reported to date are either bulk materials or thin films, and there is a general lack of research into sulfur-rich polymer colloids. Water-dispersed, sulfur-rich particles are anticipated to broaden the range of applications for sulfur-containing materials. In this study, the preparation and size control parameters are presented of an aqueous dispersion of sulfur-rich polymers with the sulfur content of dispersed particles exceeding 75 wt%. Employing polymeric stabilizers with varying hydrophilic-lipophilic balance (HLB), along with changing the rank of inorganic polysulfides, allow for the control of particle size in the range of 360 nm - 1.8 µm. The sulfur-rich colloid demonstrates antioxidant properties in water, demonstrating the potential for the use of sulfur-rich polymeric materials readily removable, heterogeneous radical scavengers.

Ring-Opening Terpolymerisation of Elemental Sulfur Waste with Propylene Oxide and Carbon Disulfide via Lithium Catalysis

Elemental sulfur, a waste product of the oil refinement process, represents a promising raw material for the synthesis of degradable polymers. We show that simple lithium alkoxides facilitate the polymerisation of elemental sulfur S8 with industrially relevant propylene oxide (PO) and CS2 (a base chemical sourced from waste S8 itself) to give poly(monothiocarbonate-alt-Sx) in which x can be controlled by the amount of supplied sulfur. The in situ generation of thiolate intermediates obtained by a rearrangement, which follows CS2 and PO incorporation, allows to combine S8 and epoxides into one polymer sequence that would otherwise not be possible. Mechanistic investigations reveal that alkyl oligosulfide intermediates from S8 ring opening and sulfur chain length equilibration represent the better nucleophiles for inserting the next PO if compared to the trithiocarbonates obtained from the competing CS2 addition, which causes the sequence selectivity. The polymers can be crosslinked in situ with multifunctional thiols to yield reprocessable and degradable networks. Our report demonstrates how mechanistic understanding allows to combine intrinsically incompatible building blocks for sulfur waste utilisation.

Step-growth Polymerization of Aziridines with Elemental Sulfur: Easy Access to Linear Polysulfides and Their Use as Recyclable Adhesives

The bulk radical polymerization of bis(aziridine) with molten elemental sulfur resulted in brittle, cross-linked polymers. However, when the bis(aziridine) was treated with elemental sulfur in the presence of an organobase, the ring-opening reaction of aziridine with oligosulfide anions occurred, leading to the formation of linear polymers by step-growth polymerization. These newly synthesized polymers possess repeating units containing a sulfonamide or amide functional moiety and oligosulfide bonds with an average sulfur segment of about two. A small molecular model reaction confirmed the nucleophilic addition reaction of elemental sulfur to aziridine. It was verified that S-S dynamic bond exchange takes place in the presence of an organic base within the linear chains. The mixture of the synthesized polysulfides with pyridine exhibits exceptional adhesive properties when applied to steel, and aluminum substrates. Notably, these prepared adhesives displayed good reusability due to the dynamic S-S exchange and complete recyclability due to their solution processability. This elemental sulfur-involved polymerization approach represents an innovative method for the synthesis of advanced sulfur-containing polymers, demonstrating the potential for various applications in adhesives and beyond.

Dithiophosphoric Acids for Polymer Functionalization

Dithiophosphoric acids (DTPAs) are an intriguing class of compounds that are sourced from elemental sulfur and white phosphorus and are prepared from the reaction of phosphorus pentasulfide with alcohols. The electrophilic addition of DTPAs to alkenes and unsaturated olefinic substrates is a known reaction, but has not been applied to polymer synthesis and polymer functionalization. We report on the synthesis and application of DTPAs for the functionalization of challenging poly-enes, namely polyisoprene (PI) and polynorbornene (pNB) prepared by ring-opening metathesis polymerization (ROMP). The high heteroatom content within DTPA moieties impart intriguing bulk properties to poly-ene materials after direct electrophilic addition reactions to the polymer backbone introducing DTPAs as side chain groups. The resulting materials possess both enhanced optical and flame retardant properties vs the poly-ene starting materials. Finally, we demonstrate the ability to prepare crosslinked polydiene films with di-functional DTPAs, where the crosslinking density and thermomechanical properties can be directly tuned by DTPA feed ratios.

Amine-Decorated Methacrylic Acid-based Inverse Vulcanized Polysulfide for Effective Mercury Removal from Wastewater

Mercury [Hg(II)] contamination is an indefatigable global hazard that causes severe permanent damage to human health. Extensive research has been carried out to produce mercury adsorbents; however, they still face certain challenges, limiting their upscaling. Herein, we report the synthesis of a novel amine-impregnated inverse vulcanized copolymer for effective mercury removal. Poly(S-MA) was prepared using sulfur and methacrylic acid employing the inverse vulcanization method, followed by functionalization. The polyethylenimine (PEI) was impregnated on poly(S-MA) to increase the adsorption active sites. The adsorbent was then characterized byusing Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). FTIR spectroscopy confirmed the formation of the copolymer, and successful impregnation of PEI and SEM revealed the composite porous morphology of the copolymer. Amine-impregnated copolymer [amine@poly(S-MA)] outperformed poly(S-MA) in mercury as it showed 20% superior performance with 44.7 mg/g of mercury adsorption capacity. The adsorption data best fit the pseudo-second-order, indicating that chemisorption is the most effective mechanism, in this case, indicating the involvement of NH2 in mercury removal. The adsorption is mainly a monolayer on a homogeneous surface as indicated by the 0.76 value of Redlich-Peterson exponent (g), which describes the adsorption nature advent from the R2 value of 0.99.

The Role of Dithiocarbamate Catalysts in the Diversification of Sulfur Speciation Towards Anionic Sulfur

Recently, there has been growing interest in the implementation of various "catalysts" to further diversify the substrate scope for inverse vulcanization reactions. While there have been several proposals on the mechanism of how these catalysts work, the speciation of sulfur in these mixtures has remained elusive. As a key component to understanding when and if these catalysts are appropriate, we sought to elucidate the role of dithiocarbamate species in inverse vulcanization reactions by attempting to characterize the speciation of sulfur. The reaction efficacy for various substrates containing different functional groups with sulfur, either with or without a metal dithiocarbamate, potassium diethyldithiocarbamate (K-DTC), suggests the formation of a rapidly fluctuating sulfur speciation and, most importantly, the presence of anionic sulfur. The work concludes with some suggestions on best practices for the utilization of dithiocarbamate catalysts based on our results.

Base-Assisted Polymerizations of Elemental Sulfur and Alkynones for Temperature-Controlled Synthesis of Polythiophenes or Poly(1,4-dithiin)s

With the increasing demand for functional polythiophenes in extensive applications such as organic solar cells, electronic skins, thermoelectric materials, and field effect transistors, efficient and economic synthetic approaches for polythiophenes are urgently required. In this work, KOH-assisted polymerizations of elemental sulfur and alkynones were developed to directly afford polythiophenes with various backbones, regioselective structures, and high molecular weights (Mns up to 20700 g/mol) in high yields (up to 97%) at 80 °C in 30 min. When the same polymerization was conducted at room temperature, stable and unique poly(1,4-dithiin)s (Mns up to 21800 g/mol) could be rapidly obtained in high yields (up to 87%) in 10 min. The temperature-controlled KOH-assisted polymerizations of sulfur and alkynones possessed high efficiency, mild conditions, and simple operation, which had provided an economic, efficient, and convenient approach for the direct conversion from elemental sulfur to functional polythiophenes and poly(1,4-dithiin)s with the in situ constructed aromatic or nonaromatic heterocycles embedded in the polymer backbones, demonstrating great synthetic simplicity, high efficiency, good selectivity, and robustness. It is anticipated to accelerate the development of semiconducting polymer materials and their applications.

Controlled and Regioselective Ring-Opening Polymerization for Poly(disulfide)s by Anion-Binding Catalysis

Poly(disulfide)s are an emerging class of sulfur-containing polymers with applications in medicine, energy, and functional materials. However, the constituent dynamic covalent S-S bond is highly reactive in the presence of the sulfide (RS-) anion, imposing a persistent challenge to control the polymerization. Here, we report an anion-binding approach to arrest the high reactivity of the RS- chain end to control the synthesis of linear poly(disulfide)s, realizing a rapid, living ring-opening polymerization of 1,2-dithiolanes with narrow dispersity and high regioselectivity (Mw/Mn ∼ 1.1, Ps ∼ 0.85). Mechanistic studies support the formation of a thiourea-base-sulfide ternary complex as the catalytically active species during the chain propagation. Theoretical analyses reveal a synergistic catalytic model where the catalyst preorganizes the protonated base and anionic chain end to establish spatial confinement over the bound monomer, effecting the observed regioselectivity. The catalytic system is amenable to monomers with various functional groups, and semicrystalline polymers are also obtained from lipoic acid derivatives by enhancing the regioselectivity.

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.

Response surface optimization of process parameters for preparation of cellulose nanocrystal stabilized nanosulphur suspension

This study employed response surface methodology (RSM) to optimize various parameters involved in the synthesis of nanosulphur (NS) stabilized by cellulose nanocrystals (CNCs). The elemental sulphur (ES) mixed with CNCs was processed in a high-pressure homogenizer to make a stable formulation of CNC-stabilized NS (CNC-NS). RSM was adopted to formulate the experiments using Box-Behnken design (BBD) by considering three independent variables i.e., ES (5, 10, 15 g), CNCs (25, 50, 75 ml), and the number of passes (NP) in the high-pressure homogenizer (1, 2, 3). For the prepared suspensions (CNC-NS), the range of the responses viz. settling time (0.84-20.60 min), particle size (500.41-1432.62 nm), viscosity (29.20-420.60 cP), and surface tension (60.35-73.61 N/m) were observed. The numerical optimization technique was followed by keeping the independent and dependent factors in the range yielded in the optimized solution viz. 46 ml (CNCs), 8 g (ES), and 2 (NP). It was interpreted from the findings that the stability of the suspension had a positive correlation with the amount of CNC while the increasing proportion of ES resulted in reduced stability. The quadratic model was fitted adequately to all the responses as justified with the higher coefficient of determination (R2 ≥ 0.88). The characterization performed by X-ray diffraction (XRD), zeta potential, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) revealed better-stabilizing properties of the optimized CNCs-ES suspension. The study confirmed that CNCs have the potential to be utilized as a stabilizing agent in synthesizing stable nanosulphur formulation by high-pressure homogenization.

Unraveling the rheology of inverse vulcanized polymers

Multiple relaxation times are used to capture the numerous stress relaxation modes found in bulk polymer melts. Herein, inverse vulcanization is used to synthesize high sulfur content (≥50 wt%) polymers that only need a single relaxation time to describe their stress relaxation. The S-S bonds in these organopolysulfides undergo dissociative bond exchange when exposed to elevated temperatures, making the bond exchange dominate the stress relaxation. Through the introduction of a dimeric norbornadiene crosslinker that improves thermomechanical properties, we show that it is possible for the Maxwell model of viscoelasticity to describe both dissociative covalent adaptable networks and living polymers, which is one of the few experimental realizations of a Maxwellian material. Rheological master curves utilizing time-temperature superposition were constructed using relaxation times as nonarbitrary horizontal shift factors. Despite advances in inverse vulcanization, this is the first complete characterization of the rheological properties of this class of unique polymeric material.

Super Adhesive Fluorescent Materials for Encrypted Messages, Underwater Leak Repair, and Their Potential Application in Fluorescent Tattoos

Achieving high-performance luminescence for underwater bonding remains a significant challenge in materials science. This study addresses this issue by synthesizing a luminescent material based on an aggregation-induced emission (AIE) monomer and copolymerizing it with lipoic acid (LA) to create an AIE supramolecular polymer. The resulting copolymer exhibits strong fluorescence under ultraviolet (UV) irradiation at 365 nm due to the AIE of TPEE and enables underwater adhesion. The P(LA-TPEE) polymer demonstrates potential for digital encryption and decryption of quick response (QR) codes underwater. Furthermore, it can dissolve well in anhydrous ethanol, producing an environment-friendly and super waterproof adhesive. Most notably, the P(LA-TPEE) solution can be sprayed on human skin, creating an invisible tattoo that only became visible under UV light due to the hydrogen bond (H-bond) and π-π structures. This smart tattoo can be quickly wiped away with alcohol, avoiding the painful and harmful process of tattoo removal. It can also be repeatedly applied to draw the preferred tattoo pattern. This AIE supramolecular polymer shows great potential in underwater adhesion and repair, underwater message encryption, and non-toxic and painless invisible tattooing. Overall, this study provides a valuable approach for material design in the future.

Precise construction of weather-sensitive poly(ester-alt-thioesters) from phthalic thioanhydride and oxetane

We report the selective ring opening copolymerisation (ROCOP) of oxetane and phthalic thioanhydride by a heterobimetallic Cr(III)K catalyst precisely yielding semi-crystalline alternating poly(ester-alt-thioesters) which show improved degradability due to the thioester links in the polymer backbone.

Precise cooperative sulfur placement leads to semi-crystallinity and selective depolymerisability in CS2/oxetane copolymers

CS₂ promises easy access to degradable sulfur-rich polymers and insights into how main-group derivatisation affects polymer formation and properties, though its ring-opening copolymerisation is plagued by low linkage selectivity and small-molecule by-products. We demonstrate that a cooperative Cr(III)/K catalyst selectively delivers poly(dithiocarbonates) from CS₂ and oxetanes while state-of-the-art strategies produce linkage scrambled polymers and heterocyclic by-products. The formal introduction of sulfur centres into the parent polycarbonates results in a net shift of the polymerisation equilibrium towards, and therefore facilitating, depolymerisation. During copolymerisation however, the catalyst enables near quantitative generation of the metastable polymers in high sequence selectivity by limiting the lifetime of alkoxide intermediates. Furthermore, linkage selectivity is key to obtain semi-crystalline materials that can be moulded into self-standing objects as well as to enable chemoselective depolymerisation into cyclic dithiocarbonates which can themselves serve as monomers in ring-opening polymerisation. Our report demonstrates the potential of cooperative catalysis to produce previously inaccessible main-group rich materials with beneficial chemical and physical properties.

Chemically Recyclable Dithioacetal Polymers via Reversible Entropy-Driven Ring-Opening Polymerization

In a sustainable circular economy, polymers capable of chemical recycling to monomers are highly desirable. We report an efficient monomer-polymer recycling of polydithioacetal (PDTA). Pristine PDTAs were readily synthesized from 3,4,5-trimethoxybenzaldehyde and alkyl dithiols. They then exhibited depolymerizability via ring-closing depolymerization into macrocycles, followed by entropy-driven ring-opening polymerization (ED-ROP) to reform the virgin polymers. High conversions were obtained for both the forward and reverse reactions. Once crosslinked, the network exhibited thermal reprocessability enabled by acid-catalyzed dithioacetal exchange. The network retained the recyclability into macrocyclic monomers in solvent which can repolymerize to regenerate the crosslinked network. These results demonstrated PDTA as a new molecular platform for the design of recyclable polymers and the advantages of ED-ROP for which polymerization is favored at higher temperatures.

On the Mechanism of the Inverse Vulcanization of Elemental Sulfur: Structural Characterization of Poly(sulfur-random-(1,3-diisopropenylbenzene))

Organosulfur polymers, such as those derived from elemental sulfur, are an important new class of macromolecules that have recently emerged via the inverse vulcanization process. Since the launching of this new field in 2013, the development of new monomers and organopolysulfide materials based on the inverse vulcanization process is now an active area in polymer chemistry. While numerous advances have been made over the last decade concerning this polymerization process, insights into the mechanism of inverse vulcanization and structural characterization of the high-sulfur-content copolymers that are produced remain challenging due to the increasing insolubility of the materials with a higher sulfur content. Furthermore, the high temperatures used in this process can result in side reactions and complex microstructures of the copolymer backbone, complicating detailed characterization. The most widely studied case of inverse vulcanization to date remains the reaction between S₈ and 1,3-diisopropenylbenzene (DIB) to form poly(sulfur-random-1,3-diisopropenylbenzene)(poly(S-r-DIB)). Here, to determine the correct microstructure of poly(S-r-DIB), we performed comprehensive structural characterizations of poly(S-r-DIB) using nuclear magnetic resonance spectroscopy (solid state and solution) and analysis of sulfurated DIB units using designer S-S cleavage polymer degradation approaches, along with complementary de novo synthesis of the sulfurated DIB fragments. These studies reveal that the previously proposed repeating units for poly(S-r-DIB) were incorrect and that the polymerization mechanism of this process is significantly more complex than initially proposed. Density functional theory calculations were also conducted to provide mechanistic insights into the formation of the derived nonintuitive microstructure of poly(S-r-DIB).

Electrochemical Synthesis of Poly(trisulfides)

With increasing interest in high sulfur content polymers, there is a need to develop new methods for their synthesis that feature improved safety and control of structure. In this report, electrochemically initiated ring-opening polymerization of norbornene-based cyclic trisulfide monomers delivered well-defined, linear poly(trisulfides), which were solution processable. Electrochemistry provided a controlled initiation step that obviates the need for hazardous chemical initiators. The high temperatures required for inverse vulcanization are also avoided resulting in an improved safety profile. Density functional theory calculations revealed a reversible "self-correcting" mechanism that ensures trisulfide linkages between monomer units. This control over sulfur rank is a new benchmark for high sulfur content polymers and creates opportunities to better understand the effects of sulfur rank on polymer properties. Thermogravimetric analysis coupled with mass spectrometry revealed the ability to recycle the polymer to the cyclic trisulfide monomer by thermal depolymerization. The featured poly(trisulfide) is an effective gold sorbent, with potential applications in mining and electronic waste recycling. A water-soluble poly(trisulfide) containing a carboxylic acid group was also produced and found to be effective in the binding and recovery of copper from aqueous media.

Direct Synthesis of Thioesters from Feedstock Chemicals and Elemental Sulfur

The development of a mild, atom- and step-economical catalytic strategy that effectively generates value-added molecules directly from readily available commodity chemicals is a central goal of organic synthesis. In this context, the thiol-ene click chemistry for carbon-sulfur (C-S) bond construction has found widespread applications in the synthesis of pharmaceuticals and functional materials. In contrast, the selective carbonyl thiyl radical addition to carbon-carbon multiple bonds remains underdeveloped. Herein, we report a carbonyl thiyl radical-based thioester synthesis through three-component coupling from feedstock aldehydes, alkenes, or alkynes and elemental sulfur by direct photocatalyzed hydrogen atom transfer. This method represents an orthogonal strategy to the conventional thiol-based nucleophilic substitution and exhibits a remarkably broad substrate scope ranging from simple commodity chemicals such as ethylene and acetylene to complex pharmaceutical molecules. This protocol can be easily extended to the synthesis of thiolactones, oligomer/polymers, and thioacids. Its synthetic utility has been demonstrated by a two-step synthesis of the drug esonarimod. Mechanistic studies indicate that the use of elemental sulfur to trap acyl radicals is both thermodynamically and kinetically favored, illustrating its great potential for the synthesis of sulfur-containing molecules.

Poly(dithiophosphate)s, a New Class of Phosphorus- and Sulfur-Containing Functional Polymers by a Catalyst-Free Facile Reaction between Diols and Phosphorus Pentasulfide

Novel poly(dithiophosphate)s (PDTPs) were successfully synthesized under mild conditions without any additive in the presence of THF or toluene diluents at 60 °C by a direct, catalyst-free reaction between the abundant phosphorus pentasulfide (P₄S₁₀) and glycols such as ethylene glycol (EG), 1,6-hexanediol (HD) and poly(ethylene glycol) (PEG). GPC, FTIR, ¹H and ³¹P NMR analyses proved the formation of macromolecules with dithiophosphate coupling groups having P=S and P-SH pendant functionalities. Surprisingly, the ring-opening of THF by the P-SH group and its pendant incorporation as a branching point occur during polymerization. This process is absent with toluene, providing conditions to obtain linear chains. ³¹P NMR measurements indicate long-time partial hydrolysis and esterification, resulting in the formation of a thiophosphoric acid moiety and branching points. Copolymerization, i.e., using mixtures of EG or HD with PEG, results in polymers with broadly varying viscoelastic properties. TGA shows the lower thermal stability of PDTPs than that of PEG due to the relatively low thermal stability of the P-O-C moieties. The low T_gs of these polymers, from -4 to -50 °C, and a lack of PEG crystallites were found by DSC. This polymerization process and the resulting novel PDTPs enable various new routes for polymer synthesis and application possibilities.

Transcending the Trade-off in Refractive Index and Abbe Number for Highly Refractive Polymers: Synergistic Effect of Polarizable Skeletons and Robust Hydrogen Bonds

High-refractive-index polymers (HRIPs) are attractive materials for the development of optical devices with high performances. However, because practical components and structures for HRIPs are limited from the viewpoint of synthetic techniques, it has proved difficult using traditional strategies to enhance the refractive index (RI) of HRIPs to more than a certain degree (over 1.8) while maintaining their visible transparency. Here, we found that poly(phenylene sulfide) (PPS) derivatives featuring both methylthio and hydroxy groups can simultaneously exhibit balanced properties of an ultrahigh RI of n _D = 1.85 and Abbe number of ν_D = 20 owing to the synergistic effect of high molar refraction and dense intermolecular hydrogen bonds (H-bonds). This brand new strategy is anticipated to contribute to the development of HRIPs displaying ultrahigh RI with adequate Abbe numbers beyond the empirical n _D-ν_D threshold, which has not been achieved to date.

Mechanochemical synthesis of inverse vulcanized polymers

Inverse vulcanization, a sustainable platform, can transform sulfur, an industrial by-product, into polymers with broad promising applications such as heavy metal capture, electrochemistry and antimicrobials. However, the process usually requires high temperatures (≥159 °C), and the crosslinkers needed to stabilize the sulfur are therefore limited to high-boiling-point monomers only. Here, we report an alternative route for inverse vulcanization—mechanochemical synthesis, with advantages of mild conditions (room temperature), short reaction time (3 h), high atom economy, less H₂S, and broader monomer range. Successful generation of polymers using crosslinkers ranging from aromatic, aliphatic to volatile, including renewable monomers, demonstrates this method is powerful and versatile. Compared with thermal synthesis, the mechanochemically synthesized products show enhanced mercury capture. The resulting polymers show thermal and light induced recycling. The speed, ease, versatility, safety, and green nature of this process offers a more potential future for inverse vulcanization, and enables further unexpected discoveries.

Inverse vulcanization is a process that enables to convert sulfur, a by-product of the petroleum industry, into polymers. Here the authors report a synthetic method of inverse vulcanization via mechanochemical synthesis; compared to thermal routes, a broader range of monomers can be used, and the protocol yields materials with enhanced mercury capture capacity.

Thermochemistry and Kinetics of the Atmospheric Oxidation Reactions of Propanesulfinyl Chloride Initiated by OH Radicals: A Computational Approach

The thermochemistry and kinetics of the atmospheric oxidation mechanism for propanesulfinyl chloride (CH₃-CH₂-CH₂-S(═O)Cl; PSICl) initiated by the hydroxyl (OH) radical were investigated with high level quantum chemistry calculations and the Master equation solver for multi-energy well reaction (Mesmer) kinetic code. The mechanism for the oxidation of PSICl in the presence of OH radical can proceed via H-abstraction and substitution pathways. The CCSD(T)/aug-cc-pV(T+d)Z//MP2/aug-cc-pV(T+d)Z level calculated energies revealed addition of the OH radical to the S-atom of the sulfinyl (-S(═O)) moiety, followed by cleavage of the Cl-S(═O) single bond, leading to formation of propanesulfinic acid (PSIA) and the Cl radical to be the major pathway when compared to all other possible channels. The transition state barrier height for this reaction was found to be -3.0 kcal mol^-1 relative to the energy of the starting PSICl + OH radical reactants. The rate coefficients were calculated for all possible paths in the atmospherically relevant temperature range of 200-320 K and at 1 atm. The rate coefficient for the formation of the PSIA + Cl radical from the PSICl + OH radical reaction was found to be 8.2 × 10^-12 cm³ molecule^-1 s^-1 at 298 K and a pressure of 1 atm. From branching ratio calculations, it was revealed that the reaction resulting in the formation of the PSIA + Cl radical contributed ∼52% to the total reaction. The overall rate coefficient for the PSICl + OH reaction was also calculated and found to be 1.6 × 10^-11 cm³ molecule^-1 s^-1 at 298 K and a pressure of 1 atm. In the aggregate, the results indicate the atmospheric lifetime of PSICl to be ∼12-20 h in the temperature range between 200 and 320 K, which suggests that its contribution to global warming is negligible. However, the degradation products revealed to be formed in its interactions with the OH radical, which include that SO₂, Cl radical, HO₂ radical, and propylene have significant effects on the formation of acid rain, secondary organic aerosols, the ozone layer, and global warming.

Modelling mercury sorption of a polysulfide coating made from sulfur and limonene

A polymer made from sulfur and limonene was used to coat silica gel and then evaluated as a mercury sorbent. A kinetic model of mercury uptake was established for a range of pH values and concentrations of sodium chloride. Mercury uptake was generally rapid from pH = 3 to pH = 11. At neutral pH, the sorbent (500 mg with a 10 : 1 ratio of silica to polymer) could remove 90% of mercury within one minute from a 100 mL solution containing 5 ppm HgCl₂ and 99% over 5 minutes. It was found that sodium chloride, at concentrations comparable to seawater, dramatically reduced mercury uptake rates and capacity. It was also found that the spent sorbent was stable in acidic and neutral media, but degraded at pH 11 which led to mercury leaching. These results help define the conditions under which the sorbent could be used, which is an important advance for using this material in remediation processes.

Bitumen Binders Modified with Sulfur/Organic Copolymers

With the continuing growth of waste sulfur production from the petroleum industry processes, its utilization for the production of useful, low-cost, and environmentally beneficial materials is of primary interest. Elemental sulfur has a significant and established history in the modification of bitumen binders, while the sulfur-containing high-molecular compounds are limited in this field. Herein, we report a novel possibility to utilize the sulfur/organic copolymers obtained via the inverse vulcanization process as modifiers for bitumen binders. Synthesis and thermal characterization (TGA-DSC) of polysulfides derived from elemental sulfur (S8) and unsaturated organic species (dicyclopentadiene, styrene, and limonene) have been carried out. The performance of modified bitumen binders has been studied by several mechanical measurements (softening point, ductility, penetration at 25 °C, frass breaking point, adhesion to glass and gravel) and compared to the unmodified bitumen from the perspective of normalized requirements concerning polymer-modified bitumen. The interaction of bitumen binder with sulfur/organic modifier has been studied by means of FTIR spectroscopy and DSC measurements. The impact of the modification on the performance properties of bitumen has been demonstrated. The bitumen binders modified with sulfur/organic copolymers are in general less sensitive to higher temperatures (higher softening point up to 7 °C), more resistant to permanent deformations (lower penetration depth), and more resistant to aging processes without intrusive deterioration of parameters at lower temperatures. What is more, the modification resulted in significantly higher adhesion of bitumen binders to both glass (from 25% up to 87%) and gravel surfaces in combination with a lower tendency to form permanent deformations (more elastic behavior of the modified materials).

A comparison of adhesive polysulfides initiated by garlic essential oil and elemental sulfur to create recyclable adhesives

Sulfur and garlic essential oil can initiate polymerization with a variety of natural monomers to form sustainable adhesives. The sulfur source has a substantial impact on the adhesion strength and material properties.

Magnetic responsive composites made from a sulfur-rich polymer

A magnetic responsive composite was made from a sulfur-rich polymer and iron nanoparticles. Diverse applications in mercury remediation, microwave curing, and magnetic responsive actuators were demonstrated.

Synthesis and characterization of polysulfides formed by the inverse vulcanisation of cyclosiloxanes with sulfur

Inverse vulcanisation stabilizes polysulfide chains through cross-linking. This research focuses on the incorporation of cyclosiloxane cross-linkers containing multiple alkene moieties, namely tetravinyl-tetramethyl-cyclotetrasiloxane (TVTSi) and pentavinyl-pentamethyl-cyclopentasiloxane (PVPSi). Both siloxanes underwent successful...

Tracking side reactions of the inverse vulcanization process and developing monomer selection guidelines

Various olefin monomers were inverse-vulcanized. The structural analysis and evaluation of the thermal stability of the products revealed that aliphatic internal olefins are suitable monomers for suppressing side reactions.

Thermally highly stable polyhedral oligomeric silsesquioxane (POSS)-sulfur based hybrid inorganic/organic polymers: synthesis, characterization and removal of mercury ion

Elemental sulfur was copolymerized with octavinyl polyhedral oligomeric silsesquioxane (OV-POSS) cages in diglyme solution via the inverse vulcanization method and characterized using NMR and FTIR spectroscopic techniques.

Sulfur-Dipentene polysulfides: from industrial waste to sustainable, low-cost materials

The synthesis of poly(S-dipentene) with a sulfur content greater than 50 wt % by catalytic inverse vulcanization in the presence of zinc-based accelerators was investigated at 140 °C for the...

Incorporation of fillers to modify the mechanical performance of inverse vulcanised polymers

Inverse vulcanisation stabilises polymeric sulfur to synthesise high sulfur content polymers. Inverse vulcanised polymers were reinforced with carbon black, cellulose microfibres and nanoclay to increase tensile strength.

Facile construction of functional poly(monothiocarbonate)s copolymers under mild operating conditions

The installation of both oxazolidone and thiocarbonate linkages within a single polymer backbone remains elusive by simple procedures under mild conditions. In this work, we report the construction of copolymers...