Polysulfide Groups Research Articles

A new perspective on the photochromism and polysulfide radical changes in sodalite

In this paper, the photochromic mechanism of different colors of sodalite and the changes in polysulfide radicals after photochromism were investigated. The results show that the substitution of chlorine by polysulfide radicals forms the basis for photochromism, and two structural defects—chlorine vacancies and oxygen hole centers are involved in the photochromism of sodalite. The decrease in the concentration of polysulfide radical S2− after photochromism leads to reduction in fluorescence intensity. This study explores the reasons for the change in fluorescence intensity caused by the alteration of polysulfide radicals after photochromism, and identifies the types of structural defects within sodalite.

Rock-forming feldspathoids of the sodalite–sapozhnikovite series from the Lovozero alkaline complex (Kola peninsula, Russia): isomorphism, thermal and radiation-induced transformations and genetic mineralogy

Sulfur-enriched sodalite-group feldspathoids from the Lovozero alkaline complex (Kola peninsula, Russia) and products of their laboratory, anthropogene, and natural thermal and radiation-induced transformations were studied using EMPA, single-crystal XRD, and Raman, IR, ESR and optical spectroscopy. Sodalite Na8[Al6Si6O24]Cl2 and sapozhnikovite Na8[Al6Si6O24](HS)2 form a continuous isomorphous series [with the Cl:HS ratio variation (in mol.%) from Cl100(HS)0 to Cl12(HS)88] in highly agpaitic feldspathoid syenites and their pegmatites. In Lovozero, hydrosulfide anion HS— turned out the major form of sulfidic sulfur occurrence in minerals of this group including sodalite-hackmanite. It is found that sapozhnikovite and HS-rich sodalite are important rock-forming minerals of some Lovozero rocks; a new rock, poikilitic nepheline-sapozhnikovite syenite was discovered. Sapozhnikovite and intermediate members of the sodalite–sapozhnikovite series are the sensitive geochemical indicator, an oxymeter which indicates reducing conditions of mineral formation. Under heating, HS− anion in sodalite-sapozhnikovite series minerals destroys and sulfur forms polysulfide groups: radical anion S2●− (500–600 °C) and further radical anion S3●− (700 °C and above). The S3●− groups also appear in the result of radiation-induced transformation of these minerals. Under natural radioactive irradiation at the contact with Th-enriched steenstrupine, an intermediate member of the sodalite-sapozhnikovite series transformed to an earlier unknown in nature S3●−-rich variety of sodalite with the simplified formula Na8[Al6Si6O24][Cl,(S3)].

APPLICATION OF SULFUR RADICAL ANIONS IN ORGANIC SYNTHESIS. DETERMINATION OF FORMS OF SULFUR

The study of reactions involving sulfur anion radicals in organic synthesis has become an area of active research in the last few years. The role of polysulfide radicals in the electrochemical processes of lithium-sulfur (Li-S) batteries has been particularly discussed. Understanding the pathways of the electrochemical reactions is crucial for improving the performance of Li-S batteries. In order to summarize and analyze the most relevant literature data, the review presents information on the application and study of sulfur anion radicals in organic synthesis and methods for the determination of sulfur forms. We have classified and discussed in detail the spectra of various forms of sulfur in the ultraviolet and visible ranges. The article describes the choice of solvent, the correlation between the properties of solvents, the influence of the nature of the solvent on the absorption band shift of sulfur particles and on the stability of the anion radical, the identification of sulfur forms in the ultraviolet and visible spectrum regions, and the possibility of stabilizing anion radicals by complexation with crown ethers. The absorption bands for S22-, S32-, S52-, S72- strongly overlap with other particles while having lower intensities, leading to different conclusions regarding the distribution of polysulfides and different forms of sulfur in aqueous media. The data presented in the review have an applied meaning, contribute to the understanding of the application of sulfur anion radicals in organic synthesis and can be used for the choice of method for the determination of sulfur forms and solvent. This review article may be of interest to specialists in the field and will help to plan studies on the study of sulfur forms and the interpretation of spectra of different sulfur forms.

Crystal Chemistry, Thermal and Radiation-Induced Conversions and Indicatory Significance of S-Bearing Groups in Balliranoite

Crystal-chemical features of a sulfide-bearing variety of the cancrinite-group mineral balliranoite from the Tuluyskoe lapis lazuli deposit, Baikal Lake area, Siberia, Russia, have been investigated using a multimethodic approach based on infrared (IR), Raman, and electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV–Vis–near IR) absorption spectroscopy methods, luminescence spectroscopy, electron microprobe analysis, selective sorption of CO2 and H2O from annealing products, and single-crystal X-ray structure analysis. Holotype balliranoite and its sulfate analogue, davyne, were studied for comparison. The crystal-chemical formula of the studied sample from Tultuyskoe is Na5.4K0.1Ca2.4(Si6Al6O24)Cl2[(CO3)0.7(SO4)0.18S*0.95Cl0.1(H2O)0.16], where the content of the wide zeolite channel is given in square brackets; S* is total sulfide sulfur occurring as disordered S2●−, cis- and trans-S4, S52−, minor S3●−, and HS− groups. The presence of S52− and HS− groups, the absence of CO2 molecules, and the association with pyrrhotite and Fe-free pargasite indicate that the studied sample crystallized under highly reducing, low-temperature conditions, unlike holotype balliranoite whose formation was related to the Somma-Vesuvius volcanic complex, Italy. Irradiation of balliranoite from Tultuyskoe with X-rays results in the transformations of polysulfide groups other than S3●− into S3●− in accordance with the scheme: S52− → S2●− + S3●−; 3S2●− → 2S3●− + e−; S4 + S2●− + e− → 2S3●−; S4 + S2●− + e− → 2S3●−; S4 + S52− + e− → 3S3●− (e− = electron).

Crystal Chemistry, Isomorphism, and Thermal Conversions of Extra-Framework Components in Sodalite-Group Minerals

Isomorphic substitutions of extra-framework components in sodalite-group aluminosilicate minerals and their thermal conversions have been investigated using infrared, Raman, electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV–Vis–near IR) absorption spectroscopy methods and involving chemical and X-ray diffraction data. Sodalite-related minerals from gem lazurite deposits (haüyne, lazurite, and slyudyankaite) are characterized by wide variations in S-bearing extra-framework components including SO42− and various polysulfide groups (S2●−, S3●−, S4●− radical anions, and S4 and S6 neutral molecules) as well as the presence of CO2 molecules. Heating at 700 °C under reducing conditions results in the transformation of initial S-bearing groups SO42− and S3●− to a mixture of S2−, HS−, S2●−, and S4●− and transformation of CO2 to a mixture of CO32− and C2O42− or HC2O4− anionic groups. Further heating at 800 °C in air results in the decomposition of carbonate and oxalate groups, restoration of the SO42− and S3●− groups, and a sharp transformation of the framework. The HS− anion is stable only under reducing conditions, whereas the S3●− radical anion is the most stable polysulfide group. The HS−-dominant sodalite-group mineral sapozhnikovite forms a wide solid-solution series with sodalite. The conditions required for the formation of HS−- and CO20-bearing sodalite-group minerals are discussed.

Phenolic Compounds to Hinder Sulfur Crystallization in Sulfur-Extended Bitumen

This study examines the efficacy of phenolic compounds derived from plant-based sources on hindering the progress of sulfur crystallization in the bulk of bitumen. This in turn helps retain bitumen's thermo-mechanical properties over time. A mechanism that causes gradual time-dependent changes in bitumen's thermo-mechanical properties is a progressive structuring of the amorphous sulfur to form dendritic structures giving rise to sulfur crystallization. Sulfur crystallization in bituminous composites is implicated in premature crack initiation under thermal and mechanical loads, reducing the service life of bituminous composites used in roads, airports, bridge decks, and roofs. Therefore, there is a need to control sulfur crystallization in bitumen bulk. This is even more urgent since due to the recent strict limit on the allowable sulfur content of marine fuels, refineries are shifting the sulfur from fuel to bitumen leading to production of high sulfur bitumen. Here, we hypothesize that phenolic compounds can hinder sulfur crystallization, which occurs over time and alters bitumen's thermo-mechanical properties. Our laboratory characterization showed that high-sulfur bitumen modified with bio-oil derived from wood pellet had the least property change during a period of 60 days observation. Our study of molecular level interactions showed that the predominant phenolic compounds in wood pellet oil have the capability to neutralize polysulfide radicals due to their excellent capability for hydrogen donation and electron delocalization within their phenoxyl radicals. Moreover, the radical scavenging of polysulfide by the produced phenoxyl radicals is energetically favorable. Therefore, the high efficacy of wood pellet can be attributed to its high concentration of phenolic compounds hindering the formation of sulfur dendritic structures and crystallization. Accordingly, the study outcomes show the feasibility of controlling the thermo-mechanical properties of high-sulfur bitumen by hindering sulfur crystallization using phenolic compounds. A proper design and engineering of sulfur-extended bitumen informed by chemistry of bitumen's constituents contributes to resource conservation and sustainability in construction.For Table of Contents Only: Incorporation of phenol-rich bio-oils derived from wood-based biomass in the hindering sulfur self-assembly in sulfur-extended bitumen by neutralizing polysulfide radicals.

Ultramarine pigments

Abstract Ultramarine pigments are representatives of the inorganic blue pigments. They are characterized by intensive shades of blue and relatively weak violet and pink color tones. The composition of the pigments can be summarized by the formula Na7Al6Si6O24S3. The color of ultramarine is generated by incorporation of free polysulfide radicals in the structure of a sodalite-derived crystal lattice. Ultramarine pigments are synthesized using a series of complex solid-state reactions. The pigments are mainly used in plastics, paints and powder coatings and printing inks, but also in paper and paper coatings.

Sulfide-induced reduction of nitrobenzene mediated by different size fractions of rice straw-derived black carbon: A key role played by reactive polysulfide species

Here we investigated the mediation efficiency of different size fractions of rice straw-derived black carbon (BC) using sulfide-induced nitrobenzene reduction as a model system. The bulk BC was divided into three size fractions: dissolved BC (size <0.45 μm), colloidal BC (0.45 μm < size < 1 μm), and particulate BC (size > 1 μm). With the presence of BC fractions (250 mg/L) nitrobenzene reduction by Na2S was significantly facilitated, wherein the mediation efficiency was positively correlated with the BC fraction's oxygen group content in an order of particulate BC < colloidal BC ≪ dissolved BC. Consistently, the oxidation treatment of particulate BC with O3 or HNO3 improved the mediation efficiency, whereas the reduction treatment with NaBH4 reduced the mediation efficiency. The supernatant collected with dialysis or filtration of suspension of BC materials pre-reacted with Na2S could effectively reduce nitrobenzene, suggesting that reactive reducing sulfur species were produced in aqueous solutions by reacting sulfide only with BC materials. This was evidenced by the fact that polysulfides and polysulfide radicals were both detected in the supernatant. As demonstrated by electron paramagnetic resonance analysis, the quinone moieties at the surface of BC materials accepted electrons from sulfide and turned into semiquinone free radicals, consequently leading to formation of reactive reducing sulfur species and thus enhanced nitrobenzene reduction. The strong mediation efficiency on redox reactions observed for colloidal BC and dissolved BC combined with their significant mobility in subsurface environments indicate that these carbonaceous materials may play an important role in the fate process of organic contaminants as both carriers and catalysts. CapsuleThe surface quinone moieties of BC induce the formation of reactive reducing sulfur species by acting as one-electron acceptors and facilitate nitrobenzene reduction by sulfide.

Extra-Framework Content in Sodalite-Group Minerals: Complexity and New Aspects of Its Study Using Infrared and Raman Spectroscopy

Nine samples of carbonate-free sodalite-group minerals, including those with abnormally high contents of polysulfide groups, fluoride anion and carbon dioxide molecules as well as synthetic fluoraluminate sodalite-type compound Na8(Si7Al5O24)(AlF6)3–·5H2O, have been studied by means of electron microprobe analyses, infrared and Raman spectroscopy; the CO2 content was determined using the selective sorption of gaseous ignition products. This article describes a semi-quantitative method for estimating the content of carbon dioxide molecules in these minerals, based on IR spectroscopy data. The data obtained demonstrate the existence of a sulfide sodalite-group mineral with the idealized formula Na7(Si6Al6O24)(S3−)·H2O, which differs significantly from the formula Na6Ca2(Si6Al6O24)S2–2 accepted for lazurite. According to single-crystal X-ray structural analysis, in the F-rich sodalite-group mineral from the Eifel paleovolcanic region, Germany with the idealized formula Na7(Si6Al6O24)F−·nH2O fluorine occurs as an isolated F− anion, unlike synthetic F-rich sodalite-type compounds.

Development of Mn or Fe sulfides in the interlayer space of raw and Al-pillared bentonite

Preparation of metal sulfide nanoclusters (Mn or Fe) confined in the interlayer space of a bentonite either with or without previous Al2O3-pillaring was investigated by H2S-sulfidization of Mn²⁺- or Fe²⁺-exchanged Al2O3-pillared bentonite as potential strategy to control growth and mean final size of interlayered, MnS or FeS-like polynuclear nanoclusters. The materials were characterized by elemental analysis, cation exchange capacity, low-angle powder X-ray Diffraction, N2 adsorption isotherms, simultaneous thermal analysis (DTA/TGA), diffuse reflectance UV-vis spectroscopy and high-resolution X-ray photoelectron spectroscopy. Interlayered metal sulfides were successfully obtained in pretty short time of reaction (only ~12 h). Optimal set of preparation conditions was established promoting stabilization of the interlayered metal sulfides, whereas preserving typical layered stacking of the starting clay: (i) ratio H2S/M²⁺(incorporated) = 50 mol/mol (M = Mn²⁺ or Fe²⁺); (ii) temperature of sulfidization = 100 °C; (iii) 200 °C for final thermal treatment, irrespective the type of atmosphere used (inert-N2 or oxidizing-air) and (iv) acid-base neutralization prior to thermal treatment did not enhance thermal stability. The most efficient Al-pillaring was achieved with 20 meq Al³⁺/g clay in terms of both higher XRD 001 basal reflection and narrower distribution of alumina-pillars. HR-XPS and DR-UV-vis analyses of the best materials with every transition metal evidenced formation of polysulfide groups and blue-shift of the absorption signal as a consequence of the modification performed on the layered aluminosilicate. Development of Mn or Fe sulfides in the interlayer space of.... Available from: https://www.researchgate.net/publication/323399710_Development_of_Mn_or_Fe_sulfides_in_the_interlayer_space_of_raw_and_Al-pillared_bentonite [accessed Apr 18 2018].

Cytotoxic and cancer preventive activity of benzotrithioles and benzotrithiole oxides, synthetic analogues of varacins

The cytotoxic and cancer preventive activities of synthetic analogs of natural varacins with polysulfide groups were studied. Presence of a sulfoxide group was found to have no significant effect on the cytotoxicity of these compounds. At the same time, this group is important for inhibition of colony formation of tumor cells treated with tumor promoter thus demonstrating cancer preventive activity. The most promising compound appears to be a synthetic varacin C analog, sulfoxide 10a, which exhibits the cancer preventive activity at dose into 100 times lower than its cytotoxic concentrations.

Sulfur K-edge XANES of lazurite: Toward determining the provenance of lapis lazuli

Lazurite, the blue mineral found in lapis lazuli, may be a marker for the identification of provenance. Sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES) of lazurite from lapis lazuli of various locations, such as Afghanistan, Russia, Chile, the USA, Iran, Tajikistan, and Myanmar, is described. The XANES spectra reveal that several different sulfur chemistries exist within lazurite, attributed to contributions from multiple sulfur species. A peak at 2482.5eV is attributed to sulfate; an envelope of peaks between 2470 and 2475eV is attributed to polysulfide radicals, polysulfide dianions, neutral sulfur, and/or thiosulfate; and a peak at 2469.1eV is attributed to the trisulfur and/or disulfur radical(s). Also, a peak of unknown origin arises at 2466.3eV in several spectra. The spectral profile for the envelope of peaks (2470 to 2475eV) varies between samples and in some instances, within a sample. Most notably, the studied samples from Chile display two distinct peaks near 2471.7 and 2473.5eV with a local minimum at 2472.5eV, unlike the most commonly observed pattern—that typically observed for samples from Afghanistan—with a single maximum intensity near 2472.5eV. Other more subtle variations in this energy range also correlate with provenance at varying degrees.

Polysulfide Radicals Appearance in Partially Discharged Lithium-Sulfur Battery Analyzed By First-Principles Interpretations of X-Ray Absorption Spectra

The presence and role of polysulfide radicals in the electrochemical processes of lithium sulfur batteries (Li-S) is currently being debated. In particular, the radical trisulfur anion, S3 .-, has concurrently been purported as a key species or has been discounted as existing during battery operation.1,2 While radical species could be formed via a direct electrochemical pathway, the prevailing assumption is formation via the dissociation of Li2S6 to LiS3.3 It is unclear how critical the formation of polysulfide radical anions is to the remaining redox pathways.4 It is not known if the radicals are an essential intermediate for complete reduction of sulfur (or complete oxidation of Li2S). In addition, the concentration of radical anions relative to polysulfide dianion species (Li2Sx) formed during redox reactions has not yet been quantified. Recently, X-ray absorption spectroscopy (XAS) has been utilized to probe Li-S reaction mechanisms.2,4,5 If properly interpreted, sulfur K-edge XAS can provide powerful insights into the molecular species formed during the charge and discharge reactions of the Li-S battery. The challenge of interpreting spectroscopic data of Li-S chemistry has been the lack of spectral standards for isolated polysulfide species. Due to possible spontaneous polysulfide disproportionation and the establishment of equilibrium mixtures in solution, establishing standards for specific molecular species is necessarily complicated, if not impossible. As a result, fingerprinting is frequently performed using solid analogs, which may induce errors in the analysis since the correspondence between the solid and solution phase XAS is by no means guaranteed. A recent advance towards establishing standards, and thus atomistic interpretations of XAS experimental measurements, has been the use of electronic structure methods based on density functional theory (DFT). In a previous work we demonstrated that the XAS of dissolved lithium polysulfide dianion species and various polysulfide radicals can be obtained via first-principles molecular dynamics and DFT spectral simulations.7,8 In this work, XAS was performed on Li-S cells containing an ether-based electrolyte. Cells were discharged to various depths and probed using XAS at the sulfur K-edge. First principles calculations were performed to obtain XAS of single polysulfide molecules. These theoretical spectra were then used to determine the distribution of polysulfide species present in the battery electrolyte.6 This analysis revealed the presence of polysulfide radical anions in significant concentrations after early stages of discharge. Whereas previous studies probed the sulfur cathode in an attempt to directly examine the charge and discharge reaction processes, this present study explores a different question, also pertinent to Li-S cells: if cell discharge were stopped at specific points in the discharge process, what intermediate species would be present in the battery electrolyte after ample time has been given for polysulfide dissolution to occur? This question is of some importance, as real-world consumer batteries will be stopped and started as the user chooses so that it would be useful to know what species can be expected in the battery electrolyte if dissolution were to occur. Our results provide further insight into the discharge and disproportionation reactions that take place in the electrolyte during cycling.

Characterization of Polysulfide Radicals Present in an Ether‐Based Electrolyte of a Lithium–Sulfur Battery During Initial Discharge Using In Situ X‐Ray Absorption Spectroscopy Experiments and First‐Principles Calculations

The presence and role of polysulfide radicals in the electrochemical processes of lithium sulfur (Li–S) batteries is currently being debated. Here, first‐principles interpretations of measured X‐ray absorption spectra (XAS) of Li–S cells are leveraged with an ether‐based electrolyte. Unambiguous evidence is found for significant quantities of polysulfide radical species (LiS3, LiS4, and LiS5), including the trisulfur radical anion S3 −, present after initial discharge to the first discharge plateau, as evidenced by a low energy shoulder in the S K‐edge XAS below 2469 eV. This feature is not present in the XAS of cells at increased depth of discharge, which, by our analysis, exhibit increasing concentrations of progressively shorter polysulfide dianions. Through a combination of first‐principles molecular dynamics and associated interpretation of in situ XAS of Li–S cells, atomic level insights into the chemistries are provided that underlie the operation and stability of these batteries.

X-ray spectroscopy as a probe for lithium polysulfide radicals.

The discharge mechanism in lithium sulfur batteries is still unknown and has been purported to involve significant concentrations of polysulfide radicals. Methods capable of quantifying these species in solution are therefore of paramount importance to revealing electrochemical pathways. Here we utilize DFT based X-ray Absorption Spectroscopy (XAS) simulations at the sulfur K-edge to obtain the spectra of polysulfide molecules in neutral, radical (-1) and dianionic (-2) charge states. Our calculations indicate that, contrary to recent propositions, the observed low energy, pre-edge feature in S K-edge XAS near 2470 eV is not exclusively due to radical species, but rather arises predominantly from core-excitations of terminal atoms, at the ends of linear polysulfides, to σ* orbitals, consistent with our previous results for the dianionic species. We do however find a spectral feature unique to radicals, lying 0.5-1 eV below the established pre-edge, that arises from 1s → π* transitions of the terminal atoms. Existing measurements on polysulfides show no evidence for such transitions. We predict that detection of linear radicals in polysulfide mixtures using XAS is limited to high mole fractions (>20%), due to the relatively weak XAS intensity of this π* feature.

Ternary sulfides formed by plurivalent europium with other metals

A description of the presently known crystal structures of ternary sulfides containing europium is presented. Most of them are formed by divalent europium; they are divided into three classes: Classical structures, in which each cation is bonded to S and each S anion is simultaneously bonded to the two metals: M 1− x Eu x S (M ≡ Ca, Sr, Ba); R 2EuS 4 (R ≡ trivalent rare-earth ion); EuGa 2S 4, Eu 2GeS 4, Eu 3Ge 3S 9, Eu 3Sn 2S 7, Eu 3Sb 4S 9, Eu 1− x Cr 2S 4− x and Eu p NbS 2. The usual coordinations of Eu(II) in these compounds are 7–8 in mono- or dicapped trigonal prisms, 8 in square prisms. Cluster structures, observed with clusters of the second metal: EuMo 6-S 8 (Chevrel phase), Eu 2Re 6S 11 or polysulfide groups: Eu 2SnS 5. Semi-metal structures: Eu 1.1Bi 2S 4, for which some Eu(II) atoms are in semi-metallic channels. In these non-classical structures, the coordination polyhedra of Eu(II) are often strongly modified. Trivalent europium is present in MEuS 2 compounds (M ≡ IA elements), with an octahedral coordination. Mixed-valence compounds are Eu 5Sn 3S 12, Eu 2BiS 4 and Eu 2CuS 3. The sites of Eu(II) and Eu(III) are well differentiated in their structures and these compounds are, in reality, quaternary compounds.

2465. Negative ion effects in tea CO 2 lasers

Lazurite, the blue mineral found in lapis lazuli, may be a marker for the identification of provenance. Sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES) of lazurite from lapis lazuli of various locations, such as Afghanistan, Russia, Chile, the USA, Iran, Tajikistan, and Myanmar, is described. The XANES spectra reveal that several different sulfur chemistries exist within lazurite, attributed to contributions from multiple sulfur species. A peak at 2482.5 eV is attributed to sulfate; an envelope of peaks between 2470 and 2475 eV is attributed to polysulfide radicals, polysulfide dianions, neutral sulfur, and/or thiosulfate; and a peak at 2469.1 eV is attributed to the trisulfur and/or disulfur radical(s). Also, a peak of unknown origin arises at 2466.3 eV in several spectra. The spectral profile for the envelope of peaks (2470 to 2475 eV) varies between samples and in some instances, within a sample. Most notably, the studied samples from Chile display two distinct peaks near 2471.7 and 2473.5 eV with a local minimum at 2472.5 eV, unlike the most commonly observed pattern—that typically observed for samples from Afghanistan—with a single maximum intensity near 2472.5 eV. Other more subtle variations in this energy range also correlate with provenance at varying degrees.

Reaction of Radical Acceptors with Polymer Radicals formed by Mechanical Degradation of Vulcanizates

Abstract The authors investigated, by the EPR method, the kinetics of the accumulation and subsequent deterioration of polymer radicals, resulting from the mechanical degradation of sulfur and peroxide vulcanizates of SKMS-3 ARKM-15 rubbers at 80 ° K. The reaction of these radicals with a number of acceptors were also studied. The polymer radicals, independently of their nature, will deteriorate at temperatures near the Tg. Polysulfide radicals are completely destroyed at 240–250° K, the hydrocarbon radicals at 220–235° K, and the peroxide ones at 200–210° K. The peroxide radicals will react, at 80° K, with Ionol and alkylphenol disulfides to form phenoxy radicals, and with trichlorothiophenol to produce thiol radicals, but will not react with the stable nitroxide radicals or with di-(trichlorophenyl) disulfides. The carbon free radicals will react, at 150–200 ° K, with trichlorothiophenol and with alkylphenol disulfides, resulting in formation of polysulfide radicals, and, at 80° K, they will react with stable nitroxide radicals to form 2,2,6,6-tetramethyl-4-hydroxypiperidyl. The polysulfide radicals, within a temperature range of 80 to 250° K, do not react to any appreciable degree with any of the radical acceptors investigated.

Reaction of radical acceptors with polymer radicals produced by mechanical destruction of vulcanizates

Abstract The authors investigated, by the EPR method, the kinetics of the accumulation and subsequent deterioration of polymer radicals, resulting from the mechanical degradation of sulfur and peroxide vulcanizates of SKMS-3 ARKM-15 rubbers at 80 ° K. The reaction of these radicals with a number of acceptors were also studied. The polymer radicals, independently of their nature, will deteriorate at temperatures near the Tg. Polysulfide radicals are completely destroyed at 240–250° K, the hydrocarbon radicals at 220–235° K, and the peroxide ones at 200–210° K. The peroxide radicals will react, at 80° K, with Ionol and alkylphenol disulfides to form phenoxy radicals, and with trichlorothiophenol to produce thiol radicals, but will not react with the stable nitroxide radicals or with di-(trichlorophenyl) disulfides. The carbon free radicals will react, at 150–200 ° K, with trichlorothiophenol and with alkylphenol disulfides, resulting in formation of polysulfide radicals, and, at 80° K, they will react with ...

Stress relaxation of unaccelerated natural rubber–sulfur vulcanizates before and after treatment with triphenylphosphine

AbstractThe aerobic and anaerobic stress relaxation of unaccelerated natural rubber–sulfur vulcanizate networks has been examined before and after treatment with triphenylphosphine, a reagent which converts polysulfidic crosslinks into di‐ and monosulfide crosslinks. This treatment reduces the rate of anaerobic stress relaxation and makes the network more susceptible to protection by zinc dibutyldithiocarbamate against aerobic stress relaxation. Aerobic stress relaxation of the network after treatment with triphenylphosphine remains nonautocatalytic, indicating that it still contains the precursor of an antioxidant, and crosslinking continues to occur during aging, showing that the presence of polysulfide groups is not a sole prerequisite for such network formation.