Inverse Vulcanization Research Articles

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

Polysulfides cross-linked with cyclosiloxanes were synthesized, characterized and tested as solvent sorbents.

High strength, epoxy cross-linked high sulfur content polymers from one-step reactive compatibilization inverse vulcanization.

Inverse vulcanization provides a simple, solvent-free method for the preparation of high sulfur content polymers using elemental sulfur, a byproduct of refining processes, as feedstock. Despite the successful demonstration of sulfur polymers from inverse vulcanization in optical, electrochemical, and self-healing applications, the mechanical properties of these materials have remained limited. We herein report a one-step inverse vulcanization using allyl glycidyl ether, a heterobifunctional comonomer. The copolymerization, which proceeds via reactive compatibilization, gives an epoxy cross-linked sulfur polymer in a single step, as demonstrated through isothermal kinetic experiments and solid-state 13C NMR spectroscopy. The resulting high sulfur content (≥50 wt%) polymers exhibited tensile strength at break in the range of 10–60 MPa (70–50 wt% sulfur), which represents an unprecedentedly high strength for high sulfur content polymers from vulcanization. The resulting high sulfur content copolymer also exhibited extraordinary shape memory behavior along with shape reprogrammability attributed to facile polysulfide bond rearrangement.

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

Stable ter-polysulfides from bio-based low cost dipentene and crosslinkers with a sulfur content greater than 50 wt% were synthesized by catalytic inverse vulcanization. Shape persistent polystyrene-polysulfide blends able to bind Fe2+ were obtained.

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.

Correction: Carbon onion/sulfur hybrid cathodes via inverse vulcanization for lithium–sulfur batteries

Correction for ‘Carbon onion/sulfur hybrid cathodes via inverse vulcanization for lithium–sulfur batteries’ by Soumyadip Choudhury et al., Sustainable Energy Fuels, 2018, 2, 133–146, DOI: 10.1039/C7SE00452D.

Degradable Slow-Release Fertilizer Composite Prepared by Ex Situ Mixing of Inverse Vulcanized Copolymer with Urea

To improve the crop yield and nitrogen uptake efficacy, a novel slow-release urea composite fertilizer (SUCF) was developed using inverse vulcanized copolymer with better biodegradation and nutrient release longevity. Copolymers were synthesized via inverse vulcanization of jatropha oil, and their properties were evaluated using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), powdered-X-ray diffractometry (p-XRD), and scanning electron microscopy (SEM). SUCFs were developed by ex situ mixing of inverse vulcanized copolymer with urea powder using mechanical mixer, and their properties were evaluated using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR spectra of developed fertilizer possesses the urea characteristics peaks along with the undisturbed peaks representing copolymer, confirming the mechanical mixing and that no reaction took place. SEM images of the SUCFs compared with images of copolymer revealed the appearance of new isolated particles with different morphology; EDX mapping showed that these particles represent the urea added to the copolymer. Nitrogen release longevity of developed fertilizers was evaluated in both soil and distilled water. The leaching test revealed that only 70% of the total nitrogen of SUCF prepared from 50 wt% sulfur copolymer was released after 16 days of incubation in distilled water, whereas it released only 35% nitrogen after 20 days in soil. The biodegradability of all copolymers developed was investigated by burying in soil and it revealed their biodegradable nature as weight loss was observed, which increased with the increase of incubation period.

Polymerizations with Elemental Sulfur: From Petroleum Refining to Polymeric Materials

The production of elemental sulfur from petroleum refining has created a technological opportunity to increase the valorization of elemental sulfur by the synthesis of high-performance sulfur-based plastics with improved optical, electrochemical, and mechanical properties aimed at applications in thermal imaging, energy storage, self-healable materials, and separation science. In this Perspective, we discuss efforts in the past decade that have revived this area of organosulfur and polymer chemistry to afford a new class of high-sulfur-content polymers prepared from the polymerization of liquid sulfur with unsaturated monomers, termed inverse vulcanization.

Inverse Vulcanisation of Sulfur - Preparation Methods and Applications

In this paper, we present a general overview of the development of the sulfur-based polymers that have been synthesized by inverse vulcanization and therefore they are collectively referred to as inverse vulcanized sulfur. The method of inverse vulcanization was introduced in 2013. Since then many different samples of inverse vulcanized sulfur with different properties have been synthesized. At the same time, various practical applications were introduced, including the possibility of using inverse vulcanized sulfur as the active material of the Li-S batteries.

A Degradable Inverse Vulcanized Copolymer as a Coating Material for Urea Produced under Optimized Conditions.

Global enhancement of crop yield is achieved using chemical fertilizers; however, agro-economy is affected due to poor nutrient uptake efficacy (NUE), which also causes environmental pollution. Encapsulating urea granules with hydrophobic material can be one solution. Additionally, the inverse vulcanized copolymer obtained from vegetable oils are a new class of green sulfur-enriched polymer with good biodegradation and better sulfur oxidation potential, but they possess unreacted sulfur, which leads to void generations. In this study, inverse vulcanization reaction conditions to minimize the amount of unreacted sulfur through response surface methodology (RSM) is optimized. The copolymer obtained was then characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). FTIR confirmed the formation of the copolymer, TGA demonstrated that copolymer is thermally stable up to 200 °C temperature, and DSC revealed the sulfur conversion of 82.2% (predicted conversion of 82.37%), which shows the goodness of the model developed to predict the sulfur conversion. To further maximize the sulfur conversion, 5 wt% diisopropenyl benzene (DIB) as a crosslinker is added during synthesis to produce terpolymer. The urea granule is then coated using terpolymer, and the nutrient release longevity of the coated urea is tested in distilled water, which revealed that only 65% of its total nutrient is released after 40 days of incubation. The soil burial of the terpolymer demonstrated its biodegradability, as 26% weight loss happens in 52 days of incubation. Thus, inverse vulcanized terpolymer as a coating material for urea demonstrated far better nutrient release longevity compared with other biopolymers with improved biodegradation; moreover, these copolymers also have potential to improve sulfur oxidation.

Inverse Vulcanization of a Natural Monoene with Sulfur as Sustainable Electrochemically Active Materials for Lithium-Sulfur Batteries.

A novel soluble copolymer poly(S-MVT) was synthesized using a relatively quick one-pot solvent-free method, inverse vulcanization. Both of the two raw materials are sustainable, i.e., elemental sulfur is a by-product of the petroleum industry and 4-Methyl-5-vinylthiazole (MVT) is a natural monoene compound. The microstructure of poly(S-MVT) was characterized by FT-IR, 1H NMR, XPS spectroscopy, XRD, DSC SEM, and TEM. Test results indicated that the copolymers possess protonated thiazole nitrogen atoms, meso/macroporous structure, and solubility in tetrahydrofuran and chloroform. Moreover, the improved electronic properties of poly(S-MVT) relative to elemental sulfur have also been investigated by density functional theory (DFT) calculations. The copolymers are utilized successfully as the cathode active material in Li-S batteries. Upon employment, the copolymer with 15% MVT content provided good cycling stability at a capacity of ∼514 mA h g−1 (based on the mass of copolymer) and high Coulombic efficiencies (∼100%) over 100 cycles, as well as great rate performance.

Toxic Gas-Free Synthesis of Extremely Negative Triboelectric Sulfur Copolymer Blends Via Phase Separation of Fluorine-Rich Polymers

Recently, we reported surface fluorination of sulfur-based polymers to introduce a new class of extremely negative triboelectric material. However, the direct surface fluorination requires the use of toxic fluorine gas. In this study, we report the toxic gas-free synthesis of extremely negative triboelectric sulfur-rich polymers via the phase separation of a fluorine-rich polymer, poly(2,3,4,5,6-pentafluorostyrene) (PPFS), from sulfur copolymers. PPFS was physically mixed in situ during the inverse vulcanization of elemental sulfur, a by-product of petroleum refining to prepare the polymer blends. Hot pressing of the blends into films induced the phase separation of the hydrophobic PPFS; subsequently, PPFS migrates to the hydrophobic air interface to minimize the interfacial energy. A triboelectric nanogenerator (TENG) based on the phase separated blend films presented long-term stable voltage and current outputs that are 8-fold and 9-fold higher, respectively, than those of a TENG based on polytetrafluoroethylene (PTFE), a well-known extremely negative triboelectric polymer. We also demonstrate the ability of a TENG based on an 81.1 cm2-sized blend film to power 400 series-connected blue LEDs of 3.3 V; a triboelectric open-circuit voltage output of 1362.4 V is obtained under a minimal force of 30 N. The demonstrated phase-separation strategy for fluorine-rich polymers will thus provide insights for achieving low-cost, environment-friendly, and high-performance triboelectric energy harvesting.

Antibacterial Activity of Inverse Vulcanized Polymers.

Inverse vulcanization is a bulk polymerization method for synthesizing high sulfur content polymers from elemental sulfur, a byproduct of the petrochemical industry, with vinylic comonomers. There is growing interest in polysulfides as novel antimicrobial agents due to the antimicrobial activity of natural polysulfides found in garlic and onions (Tsao et al. J. Antimicrob. Chemother. 2001, 47, 665-670). Herein, we report the antibacterial properties of several inverse vulcanized polymers against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, two common causes of nosocomial infection and pathogens identified by the World Health Organization as priorities for antimicrobial development. High sulfur content polymers were synthesized with different divinyl comonomers and at different sulfur/comonomer ratios, to determine the effect of such variables on the antibacterial properties of the resulting materials. Furthermore, polymers were tested for their potential as antibacterial materials at different temperatures. It was found that the test temperature influenced the antibacterial efficacy of the polymers and could be related to the glass transition temperature of the polymer. These findings provide further understanding of the antibacterial properties of inverse vulcanized polymers and show that such polymers have the potential to be used as antibacterial surfaces.

Copolymerization of palm oil with sulfur using inverse vulcanization to boost the palm oil industry

Nowadays, most of the world’s palm oil is being produced in Malaysia and Indonesia; however, the demand for this vegetable oil as an edible oil is declining in many countries since consuming palm oil in excess can result in serious health problems. Consequently, finding new applications such as the production of bio-based polymers to make use of this cheap and abundant vegetable oil seems necessary. Herein, we report the copolymerization of palm oil with sulfur with different feed ratios via inverse vulcanization. The copolymers are then characterized using Fourier-transform infrared spectroscopy, differential scanning calorimetry and X-ray diffraction analysis. The results confirmed the formation of the polymers and their stability against depolymerization. Altogether, the obtained sulfur-palm oil copolymers showed great properties such as thermal stability up to 230°C under a nitrogen atmosphere and rubbery properties at room temperature. Although the Thermogravimetric analysis (TGA) thermograms had previously confirmed the high conversion of elemental sulfur into the polymeric structure by comparing the initial sulfur content and the final polysulfide content in the polymer, some unreacted elemental sulfur was also observed in the final product. Sulfur-palm oil (S-Palm oil) is a new green polymer that helps to find a new use for palm oil as a big industry as well as sulfur which is underutilized and left in stockpile as a byproduct in gas and petroleum refineries.

Synthesis and applications of inverse vulcanized polysulfides from bio-crosslinkers

Elemental sulfur, an industrial by-product from petroleum industries worldwide, has drawn sufficient attention to researchers. The limited scope of application has caused a colossal surplus amount of elemental sulfur stacked in the open places. Several polysulfide synthesis processes, including condensation, free-radical process, and ionic copolymerization technique, were used but resulted in unstable products. A new polymerization technique, termed inverse vulcanization, has been introduced, which enabled different types of crosslinkers for polysulfide production and their scopes to explore numerous applications. The current paper concisely reviews the evolution and advances of using vegetable oils and plant extracts in inverse vulcanization to produce polysulfides. The alluring applications and properties have also been discussed briefly.

Halogen‐Free Polyphosphazene‐Based Flame Retardant Cathode Materials for Li–S Batteries

Novel, eco‐friendly, and halogen‐free polyphosphazene‐based flame retardant (FR) cathodes for Li–S batteries are prepared by the inverse vulcanization of elemental sulfur with polybis(2‐acrylamidoethoxy)phosphazene (poly(AAE)) resulting in the covalently bonded different wt% sulfur content polymers. Due to the polar amide groups, poly(AAE)‐xS (x refer to the wt% of sulfur) composites assist in anchoring intermediate lithium polysulfide species. The structural characterizations of the poly(AAE)‐xS polymers are conducted by elemental analysis, Fourier‐transform infrared spectroscopy, differential scanning calorimeter, thermogravimetric analysis, and scanning electron microscopy. Their FR properties are elevated by calculation of the limiting oxygen index values and burning tests. Later, lithium‐ion storage mechanism of poly(AAE)‐55S polymer is evaluated, including cyclic voltammetry, rate performance tests and electrochemical impedance spectroscopy measurements. To compare with the electrochemical performance of poly(AAE)‐55S, a noncovalent blend polymer mixture and bare sulfur are also tested. It is found that covalently bonded poly(AAE)‐55S obtained by the inverse vulcanization of elemental sulfur and poly(AAE) results much pronounced capacities. Herein, new insights into the design and development of alternative cathode materials for safer Li–S batteries, both providing FR properties and good lithium polysulfides adsorption capabilities, are offered.

Influence of Component Ratio on Thermal and Mechanical Properties of Terpenoid-Sulfur Composites

Terpenoids are potentially sustainable replacements for petrochemical olefins. Sulfur is a waste product produced in large quantities from fossil fuel refining. Several composites with attractive properties have recently been made from terpenoids and sulfur. This report details the extent to which the ratio of sulfur to terpenoid and the terpenoid olefin content influences the thermal and mechanical properties of such terpenoid-sulfur composites. The terpenoids selected were diunsaturated geraniol and triunsaturated farnesol that, upon their inverse vulcanization with elemental sulfur, yield composites GerSx and FarSx, respectively (x = wt % sulfur). The wt % sulfur in the monomer feed was varied from 30–95 for this study, providing twelve materials. Mechanical analysis of these materials was undertaken by compressive and tensile strength techniques. Differential scanning calorimetric analysis revealed both polymeric and orthorhombic sulfur present in the materials with glass transition temperatures (Tg) of −37 °C to −13 °C and melt temperatures (Tm) of 119 to 104 °C. The crystallinity of composites decreases as the weight fraction of sulfur decreases and composites having the highest olefin content exhibit no detectable crystalline microstructures. The compressive strength of the materials showed increasing strength for higher olefin-content materials for both GerSx (with compressive strength of up to 32 MPa) and FarSx (with compressive strength of up to 43 MPa). The improved strength with increasing olefin content levels off at around 80–85% of terpenoid, after which point both tensile and compressive strength diminish.

Segmented Polyurethanes and Thermoplastic Elastomers from Elemental Sulfur with Enhanced Thermomechanical Properties and Flame Retardancy

AbstractThe production of elemental sulfur from petroleum refining has created a technological opportunity to increase the valorization of elemental sulfur by the creation of high‐performance sulfur based plastics with improved thermomechanical properties, elasticity and flame retardancy. We report on a synthetic polymerization methodology to prepare the first example of sulfur based segmented multi‐block polyurethanes (SPUs) and thermoplastic elastomers that incorporate an appreciable amount of sulfur into the final target material. This approach applied both the inverse vulcanization of S8 with olefinic alcohols and dynamic covalent polymerizations with dienes to prepare sulfur polyols and terpolyols that were used in polymerizations with aromatic diisocyanates and short chain diols. Using these methods, a new class of high molecular weight, soluble block copolymer polyurethanes were prepared as confirmed by Size Exclusion Chromatography, NMR spectroscopy, thermal analysis, and microscopic imaging. These sulfur‐based polyurethanes were readily solution processed into large area free standing films where both the tensile strength and elasticity of these materials were controlled by variation of the sulfur polyol composition. SPUs with both high tensile strength (13–24 MPa) and ductility (348 % strain at break) were prepared, along with SPU thermoplastic elastomers (578 % strain at break) which are comparable values to classical thermoplastic polyurethanes (TPUs). The incorporation of sulfur into these polyurethanes enhanced flame retardancy in comparison to classical TPUs, which points to the opportunity to impart new properties to polymeric materials as a consequence of using elemental sulfur.

Multifunctional Trilayer Separator for High-Performance Lithium-Sulfur Batteries Under Extreme Conditions

Lithium-ion Batteries (LIBs) have transformed mankind's lives beyond imagination in the past few decades. They have found their use in a variety of applications such as defense, transportation, portable electronics, and space explorations. To keep up with the demand, stress is applied for discovering materials with higher capacity and energy densities. High capacity anodes like silicon, tin, antimony, carbon composites have been identified. However, limited cathode materials are available at disposal viz., LiCoO2, LiMnNiCoO2, LiFePO4, LiMn2O4. Most of these cathodes have capacities <250 mAh g-1, and thus LIBs cannot keep up with the ever-growing demand from the applications. The high-theoretical capacity chemistry of lithium-sulfur comes to the rescue. It is the lightest element to be used as a cathode, which has attractive properties such as capacity of 1672 mAh g-1, economical (~$50 per metric tonne), and abundance in nature. However, chemistry suffers from three critical issues viz., poor sulfur conductivity, polysulfide shuttling, and lithium dendrite growth. To tackle the insulative sulfur and polysulfide shuttling effect approaches such as coating sulfur with metal sulfide or oxides, mesoporous carbon, conductive polymers, inverse vulcanization have been applied. Unfortunately, these techniques lead to a reduction in the energy density of the system, involve complex fabrication steps or raw materials are expensive. On the issue of lithium metal dendrites growth, electrolytic additives, exotic electrode coatings, and special shutdown separators are used. The downside to all of these is that they impede cell performance or are uneconomical.Here we report, the use of a multifunctional trilayer separator in Li-S battery to tackle all three issues simultaneously. Modified separator acted as a barricade for polysulfide from shuttling by trapping them preferably due to the favorable interactions. The performance of Li-S cells with and without modified separator was compared for long term cycling and rate studies. It was found that cells with modified separator outperformed those with pristine separator. Modified separator cell exhibited capacities of 925, 833, 644, 480, 326, 260, and 220 mAh g-1 at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 4C rates, respectively with 95% capacity retention. The choice of electrolyte affects battery performance drastically. However, using 1M LiTFSI in 1:1 (v/v) 1, 3-Dioxolane (DOL): 1, 2-Dimethoxyethane (DME) with additives, provided remarkable results at low and high-temperature ranges. At 0 ℃, the cell with the modified separator yielded about 350 mAh g-1 capacity at 0.5C over 200 cycles. The performance of the cells was stellar even at 50 ℃ with 500 mAh g-1 capacity at 0.5C rate after 100 cycles. Multiple module calorimetry provided the thermal heat signature to elucidate the safety features of the Li-S system with the modified separator and compared with the existing LIBs. High-performance Li-S batteries proposed here can be valuable to a variety of applications like defense, transportation, and space explorations, where drastic conditions affect the battery functionalities, in the times ahead.

Effect of Sulfur Chain Length on the Electrochemical Performance of Sulfur-Rich Copolymers in Li-S Batteries

Lithium-Sulfur battery is considered to be a promising next-generation candidate because of its high theoretical capacity of ~1675 mAh/g compared to current commercial batteries. However, there are challenges related to the long-term cycling of these batteries, originating from the formation of soluble lithium polysulfides species and their subsequent shuttling. Recently, we synthesized a sulfur-rich copolymer/ carbon nanofiber cathode material for Li-S batteries. The formation of a C-S bond in these sulfur-rich copolymers results in formation of organo-lithium polysulfides (OPs) instead of lithium polysulfides (PS). The copolymer is synthesized using inverse vulcanization reaction, where sulfur powder reacts with a monomer, here 1,3-di-isopropenyl benzene (DIB), at high temperatures. In this study, we varied the DIB monomer concentration, and three samples with different sulfur/DIB wt% were synthesized. We characterized these three different samples using XRD, DSC, and FTIR. The XRD results show that the sulfur-rich copolymer transitions from a crystalline material to a completely amorphous composite. Moreover, FTIR results show a redshift in the C-S peak of the sulfur-rich copolymer with increasing the monomer wt%. These results confirm that the molecular structure of the sulfur-rich copolymer is changed as a result of changing S/DIB wt ratio in the synthesis of sulfur-rich copolymers. We believe that by increasing the monomer to sulfur ratio in such copolymers, the sulfur chain length becomes shorter. Figure 1 shows the cyclic voltammetry (CV) obtained using these three different cathodes. As can be seen from this figure, two reduction peaks at ~2.3 and ~2 V represent the formation of higher and lower order Ps and OPs. However, with further increase in DIB concentration, the first reduction peak at ~2.3V disappears. We hypothesize that the disappearance of the first reduction peak can be attributed to the existence of a short sulfur chain length. To investigate the hypothesis, an in situ cell consisted of two different cathodes, one cathode with a low (sample 1) and another with a high DIB wt% (sample 2), were built on the FTIR to simultaneously collect IR spectra and CVs. The FTIR results show a redshift from 695 cm-1 to 705 cm-1 in the C-S bond for sample 1 with higher sulfur chain length (lower monomer wt%). This shift is attributed to the formation of organopolysulfides. Moreover, as the cell was discharged, multiple peaks between the lithium polysulfide region (510 to 480 cm-1) appeared, which confirms the formation of high and low order lithium polysulfides. On the other hand, when sample 2 with lower sulfur chain length (high monomer wt%) was tested, the C-S peak shifted from 704 cm-1 to 706 cm-1 only. The smaller C-S peak shift in sample 2 compared to sample 1 confirms the existence of short-chain polysulfides. Moreover, there was no lithium polysulfide peaks observed in the polysulfide region for sample 2, which confirms that the formation of loose lithium polysulfide is avoided. Figure 1

Polymers Made by Inverse Vulcanization for Use as Mercury Sorbents

Inverse vulcanization is a process in which highly abundant and low-cost elemental sulfur is copolymerized with an unsaturated organic molecule such as a polyene. This process has provided a variety of useful materials with high sulfur content—typically 50% or greater in sulfur by mass. These materials have garnered increasing interest in research as sorbents for mercury, due to the high affinity of sulfur for mercury. In this review, the features of mercury sorbents made by inverse vulcanization are presented. Additionally, case studies are provided to illustrate the variety of polymer architectures accessible with this chemistry, the versatility of these materials in mercury remediation, and prospects for industrial use.1 Introduction2 Sulfur Polymers by Inverse Vulcanization3 Sulfur Polymers as Mercury Sorbents4 Increasing Surface Area to Improve Mercury Uptake5 Crosslinker Considerations6 Sorption of Different Forms of Mercury7 Life-Cycle Management8 Conclusions and Outlook