Polysulfide Linkages Research Articles

Influence of active, nano, and functionalized zinc oxide particles on the mechanical, cytotoxicity, and thermal stability of carbon black filled SBR/NR blends

AbstractThis study examines the viability of functionalized, nano, and active zinc oxide (ZnO) as an alternative activator in styrene butadiene rubber–natural rubber (SBR–NR) blends filled with carbon black. Concerns about the environmental impact and toxicity of Zn leaching into aquatic organisms necessitate reducing the amount of ZnO in rubber compounding. The mechanical properties, crosslink density, and thermal and morphological qualities of the SBR/NR blends made with these ZnO (F2BB, N2BB, and A2BB) were studied and compared to conventional ZnO loaded blend (C5BB). Thermal stability was evaluated using thermogravimetric analysis and temperature scanning stress relaxation. A2BB showed the highest thermal stability, while F2BB exhibited a 35% increase in tensile strength and a 28% increase in elongation at break due to polysulfide linkages. N2BB and A2BB increased tensile strength by 28 and 16% compared to C5BB. Cytotoxicity of various ZnO concentrations on HT‐22 hippocampal cells was investigated, and active and nano ZnO were found to be less toxic. Using active and nano ZnO can improve the mechanical and thermal properties of the blend while reducing environmental toxicity, allowing for a 60% reduction in ZnO concentration in rubber compounds and resulting in cost savings and a sustainable alternative to conventional ZnO.

Self‐Healable and Recyclable Sulfur Rich Poly(vinyl chloride) by S–S Dynamic Bonding

AbstractIn this work, a new approach to vulcanize commercial poly(vinyl chloride) (PVC) at room temperature and in a relatively short time (4 h) by using elemental sulfur and an initiator such as Na2S.9H2O is reported. The obtained crosslinked polymer contains polysulfide linkages that facilitate recycling/self‐healing through dynamic S–S linkages. It is shown that PVC‐polysulfide networks could be reprocessed at 180 °C for three times. The thermal and spectral characterizations of the polymers before and after recycling are performed via FT‐IR, DSC, and TGA analyses. The potential use of the sulfur rich PVC‐polysulfide system as cathode material for Li‐S battery application is also investigated and the first discharge capacity is found to be around 610 mAh g−1 that later faded rapidly.

Reduction–responsive sulfur–monoterpene polysulfides in microfiber for adsorption of aqueous heavy metal

Sulfur-containing polymers such as those with polysulfide linkages in their backbone have attracted strong interest due to the ease of modifying the structure and properties of these materials. Electrospun fiber membranes have large specific surface areas, adjustable microstructures and chemical properties, and recovery. Consequently, these materials are promising candidates for applications as sorbents for heavy metal enrichment and water remediation. Herein, polymeric sulfur–monoterpene (PST) was loaded into a polyvinylidene/poly(methyl methacrylate) (PVDF/PMMA) polymer matrix by electrospinning technology to obtain a uniform and continuous fiber-based membrane. It was found that treatment with a reducing agent increased the thiol group content in PST. Then, by using the coordination and binding effect between sulfhydryl groups and metal ions, it was found that the adsorption of Cd(II), Cr(III), Ni(II) and Hg(II) ions onto the membrane was enhanced under the stimulation of reduction. The results indicated that the reduction-responsive adsorption of Hg(II) and Cd(II) was the best, with maximum adsorption values of 58 and 34 mg g−1 for each of these respective ions. In addition, the presence of sodium ions did not interfere with the adsorption of Hg(II) or Cd(II) ions. The adsorption kinetics of Hg(II) and Cd(II) ions on the reduced membrane at different times were also studied. The results revealed that the adsorption of Hg(II) and Cd(II) ions onto the reduced membrane conforms to the pseudo-second-order kinetic model. These results indicated that PST can removal of heavy metal ions from wastewater via a convenient and reusable adsorption process.

Renewable sulfur- and monoterpenes-derived polysulfides as functional crosslinker for epoxy thermosets

Polymer materials, with sulfur as the major part of the backbone structure, are gaining increasing importance because of the large abundance of sulfur and the unique features of polysulfide linkages for modifying material properties. Herein, we introduce polysulfides, which are synthesized from sulfur and monoterpenes, as poly-thiols platform for the crosslinking of epoxy, allowing flexible sulfur constituents incorporate into covalently linked networks. This synthesis can be conducted in a simple, mild, and practical one-pot procedure proceed smoothly in a solvent-free manner with high sulfur utilization to afford sulfur–monoterpene polysulfides (PST) with high sulfur content (up to 58%) and good solubility. The epoxy was cured with PST with imidazole as the catalyst, producing highly sulfur crosslinked thermosets, which is supposed to proceed via a thiol-epoxy reaction mechanism. The resulting thermoset perform good toughness, high transmittance and potential self-healing ability.

Synthesis of Poly(phenylene polysulfide) Networks from Elemental Sulfur and p-Diiodobenzene for Stretchable, Healable, and Reprocessable Infrared Optical Applications.

The synthesis and characterization of poly(phenylene polysulfide) networks (PSNs) with controlled average sulfur ranks, from elemental sulfur (ES) and p-diiodobenzene (DIB), are investigated. The PSN films, prepared via simple hot pressing, are found to possess large extensibility up to around 300% and complete recovery of shape and mechanical properties after deformation, which are attributed to the loosely cross-linked network structures mainly consisting of linear poly(phenylene polysulfide) chains. The covalent polysulfide linkages in the PSNs also exhibit dynamic behaviors under ultraviolet (UV) or thermal treatment, thus, enabling self-healing and reprocessing of the films when scratched and broken, respectively. Combined with the unique mechanical properties of the PSNs, their high refractive index and excellent infrared (IR) transparency contribute to the preparation of stretchable, healable, and reprocessable IR transmitting materials for potential deformable and stretchable optical applications.

Study of crosslink structure and dynamic mechanical properties of magnetorheological elastomer: Effect of vulcanization system

Magnetorheological elastomers are a kind of intelligent and smart materials which are mainly composed of rubbery polymers and soft magnetic particles. The role of various vulcanization systems on the crosslink structures, curing properties, and dynamic mechanical properties of natural rubber–based magnetorheological elastomer was investigated. Conventional, semi-efficient, and efficient vulcanization systems were used and compared. It was found that the content of polysulfide linkages decreased and the monosulfide linkages increased when the vulcanization system was changed from conventional to semi-efficient and efficient vulcanization systems, respectively. The crosslink density has the same tendency with the content of polysulfide linkages. In all vulcanization systems, the zero-field modulus, magnetic-induced modulus, controllability of damping, and the degree of the influence of Payne effect of the samples had an increasing trend when the crosslink density decreased. Evidence from micrographs of scanning electron microscope showed that this was because the particle chains in the low crosslink density composites were longer and more aligned. As the proportion of monosulfide linkages increased, the value of the loss factor increased and the modulus of the composites was more affected by the increasing frequency.

Transport properties of high-density polyethylene/ethylene propylene diene terpolymer blends

Polymer blends based on high-density polyethylene and ethylene propylene diene terpolymer rubber (EPDM) were prepared. The sorption and diffusion of four aliphatic hydrocarbons through the blends were studied in the temperature range of 28–58 °C. Sulfur, dicumyl peroxide (DCP), and a mixture of sulfur and DCP (mixed) were used as cross-linking agents for the blends. Of the three systems, the peroxide vulcanized blends were found to exhibit the lowest penetrant uptake. This has been explained based on the higher rigidity of the –C–C– networks than the polysulfide linkages. The aliphatic liquid penetration through the matrix increased with increase in the EPDM content in the blend. The experimental observations were correlated with the morphology of the blends. Diffusion and permeation coefficients were calculated from the sorption data. A slight deviation from the Fickian trend was observed for the mechanism of transport with an increase in EPDM in the blends. The molar mass between cross-links and thermodynamic parameters of sorption was determined from the swelling data. The experimental observations were compared with various theoretical models.

Synthesis, characterization, thermal degradation, and comparative chain dynamics studies of weak-link polysulfide polymers

Synthesis, spectroscopic and thermal characterization of two new classes of polysulfide polymers: poly[1-(phenoxymethyl) ethylene polysulfide] (PPMEP), and poly[1-(phenoxy) ethylene polysulfide] (PPEP) is presented. The direct pyrolysis mass spectrometry (DP-MS) technique, used to study the thermal degradation behavior of these polysulfide polymers, indicated that the polymers underwent degradation through the weak-links scission. The thermal stability of the polysulfide polymers decreased as the “rank” (number of sulfur atoms in the polysulfide linkage; n = 1, 2, 4) increased. The main-chain flexibility of these polysulfide polymers in terms of their 13C NMR spin-lattice relaxation time (T1) measurements on the backbone methine (-CH-) and methylene (-CH2-) carbons are reported here for the first time. A comparative study of the solution chain dynamics indicated that it increased as “rank” of the polysulfide linkages decreased as well as by introducing side chain spacers such as, ether (-O-) or methyleneoxy (-CH2O-) groups.

Characterization of Alkali Induced Formation of Lanthionine, Trisulfides, and Tetrasulfides from Peptide Disulfides using Negative Ion Mass Spectrometry

Peptide disulfides are unstable under alkaline conditions, resulting in the formation of products containing lanthionine and polysulfide linkages. Electrospray ionization mass spectrometry has been used to characterize major species obtained when cyclic and acyclic peptide disulfides are exposed to alkaline media. Studies on a model cyclic peptide disulfide (Boc-Cys-Pro-Leu-Cys-NHMe) and an acyclic peptide, oxidized glutathione, bis ((gamma)Glu - Cys - Gly - COOH), are described. Disulfide cleavage reactions are initiated by the abstraction of C(alpha)H or C(beta)H protons of Cys residues, with subsequent elimination of H(2)S or H(2)S(2). The buildup of reactive thiol species which act on intermediates containing dehydroalanine residues, rationalizes the formation of lanthionine and polysulfide products. In the case of the cyclic peptide disulfide, the formation of cyclic products is facilitated by the intramolecular nature of the Michael addition reaction of thiols to the dehydroalanine residue. Mass spectral evidence for the intermediate species is presented by using alkylation of thiol groups as a trapping method. Mass spectral fragmentation in the negative ion mode of the peptides derived from trisulfides and tetrasulfides results in elimination of S(2).

Exceptional performance of sulfonic acid-incorporated-MCM-41 mesoporous materials prepared using a silane containing polysulfide linkages in the acetylation of anisole

Sulfonic acid-incorporated-MCM-41 mesoporous materials prepared using a silane containing tetrasulfide linkages showed exceptional yields of the acetylated product in the acetylation of anisole due to their high content of strong acid sites.

An experimental study of the low-temperature sulfurization of carbohydrates

Sulfurization of carbohydrates has been suggested as an important mechanism for the preservation of organic matter. To study this process, different monosaccharides were sulfurized under laboratory conditions at relatively low temperature (50 °C). The products formed after cleavage of polysulfide linkages were analyzed using gas chromatography (GC) and gas chromatography/mass spectrometry after appropriate derivatization. Selected products were isolated by preparative GC and their structures were identified by nuclear magnetic resonance spectroscopy. During these experiments all monosaccharides were completely converted into organic sulfur compounds (OSCs) and monosaccharides with the carbonyl function replaced by sulfur formed a substantial part of the GC-amenable OSCs. The structures of other OSCs formed indicated that cleavage of C–C bonds and racemization also took place during these experiments. The yield of recoverable OSCs after cleavage of polysulfide linkages was relatively low (<5% of the starting monosaccharide), indicating that most of the sulfurization products were still non GC-amenable and thus, for example, linked through monosulfide linkages. Flash pyrolysates of the sulfurized carbohydrate material contained in all cases relatively high amounts of short-chain alkylated (C0–C5) thiophenes, comparable to those obtained from S-rich kerogen. The structure of the monosaccharide used in the experiments had no effect on the alkylthiophene distribution. These results provide experimental evidence that sulfurization of monosaccharides at relatively low temperatures can result in the formation of OSCs, most likely starting with sulfurization of the carbonyl functionality. Preservation of carbohydrates through sulfurization may thus be an important pathway of preservation of organic matter in anoxic depositional environments.

Early steroid sulfurisation in surface sediments of a permanently stratified lake (Ace Lake, Antarctica)

Surface sediments (0–25 cm) from Ace Lake (eastern Antarctica), a saline euxinic lake, were analyzed to study the early incorporation of reduced inorganic sulfur species into organic matter. The apolar fractions were shown to consist predominantly of dimeric (poly)sulfide linked C 27-C 29 steroids. These steroid moieties were identified by GC-MS analysis of the apolar fractions after cleavage of polysulfide linkages using MeLi and MeI and after desulfurisation. The polar fractions contained the oligomeric analogues. The S-bound steroids are most likely formed by sulfur incorporation into steroidal ketones formed from Δ 5 sterols by biohydrogenation by anaerobic bacteria. The concentrations of these sulfurised steroids increased with depth in the sediment. The sulfurisation reaction is completed in 1000–3000 years. Despite a wide range of functionalised lipids present in these sediments that are potentially available for sulfurisation, there is a very strong preference for the incorporation of sulfur into steroidal compounds. A predominance of sulfurised C 27 steroids contrasted with the distribution of free sterols, which showed a strong predominance of C 29 sterols. This indicates that the incorporation of sulfur is biased towards C 27 sterols. The results demonstrate that intermolecular sulfurisation of organic matter can occur in surface sediments at low temperatures and in the absence of light.

Interactions of thiols with sedimentary particulate phase: studies of 3-mercaptopropionate in salt marsh sediments from Shelter Island, New York

3-Mercaptopropionate (3-MPA) is a major hydrophilic thiol in salt marsh sediments from Shelter Island, New York. It is associated mainly with the sedimentary particulate phase, although the mechanism of its binding has not been clear. In this study, we show that humic substances coated on clay minerals are involved in binding 3-MPA through di- and poly-sulfide linkages. With increasing depth, the abundance of 3-MPA in the fulvic acid fraction decreases with a concomitant increase in the humic acid fraction, suggesting that, with depth, fulvic-bound 3-MPA is converted into humic-bound 3-MPA. We modeled the depth variation with a multi-G model which suggests that there are two types of reactive components in both fulvic acid-bound and humic acid-bound 3-MPA, one changing about 10 times more rapidly than the other. These two 3-MPA pools probably reflect different types of sulfur bridging, with the polysulfide-bridged pool changing more rapidly than the disulfide-bridged pool. As free thiol, 3-MPA is attacked relatively rapidly by anaerobic bacteria, its degradation following firstorder kinetics. However, in the sediment core we studied, humic-bound 3-MPA was present throughout the sediment column, down to 22 cm, corresponding to an age of about 90 years. These results suggest that thiols can escape bacterial degradation in sediments by binding to humic substances. The sedimentary distribution of 3-MPA is an important illustration of the interplay of biological and chemical processes in the fate of thiols in anoxic marine sediments.

Electron paramagnetic resonance spectroscopic investigation of the synthesis of poly(p-phenylene sulfide/disulfide), PPS/DS

The reaction of diiodobenzene and sulfur in air at elevated temperatures (230-300°C), has been investigated by high-temperature EPR spectroscopy. The first direct observation of radicals under conditions of poly(p-phenylene sulfide/disulfide) synthesis is reported. Radicals observed include both a sulfur radical and a carbon radical. EPR experiments with monomers indicate the importance of polysulfide linkages, such as disulfide, with and without iodine or iodo substitution for the formation of these radical species

Occurrence of particle‐bound polysulfides and significance of their reaction with organic matters in marine sediments

Inorganic polysulfides (Sn2−, where n &gt; 1) contribute to the incorporation of sulfur into organic matter in reducing sediments, especially when conditions exist for partial oxidation of sulfide. Inorganic polysulfides have been assumed previously to exist only in the aqueous phase. Our results suggest that a significant fraction of inorganic polysulfides is bound to the particulate‐phase of sediments and can react with carbon‐carbon unsaturated bonds in organic matter, thereby attaching it to the particulate phase through polysulfide linkages. This mechanism may affect the bioavailability of the reactive organic matter in sediments and hence may play an important role in the preservation of organic matter in anoxic marine sediments.

Synthesis of telechelic dithiol oligomers containing sulfur atoms‐moisture barrier properties

AbstractThe aim of this work was to synthesize new polysulfide materials from butadiene, styrene, isoprene, and methacrylate monomers and to study their moisture vapor permeability. For this purpose, a series of telechelic dithiol polysulfide oligomers were prepared by a polycondensation reaction between dianionic species of the corresponding monomer and sulfur or by reduction of the resulting cyclic polysulfide polymers. This last process was followed by 1H‐NMR and elemental analysis. It was established that the scission of the polysulfide linkages to thiol end groups was fastest with the greatest number of sequential sulfur atoms. The thiol reactivity was used to prepare cured materials from the liquid oligomers and manganese dioxide: Networks were obtained from butadiene dithiol oligomers, whereas chain extension occurred for the others. Infrared analysis suggests that the reticulation reaction results from thiol addition to the double bond. The moisture vapor transmission test applied to these different materials showed that these new compounds present good moisture barrier properties.

Chemorheological treatment of crosslinked EPDM. II

AbstractStress relaxation mechanisms were investigated on three kinds of ethylene–propylene terpolymers (EPDM), differing only in the structure of the crosslinkage, in both nitrogen and air at 160°C. The crosslinking site in these polymers consists of a carbon–carbon bond, a polysulfide linkage, and a carbon–carbon bond and a polysulfide linkage, respectively. Stress relaxation in air for peroxide‐cured EPDM was based on the oxidative scission of the main chain. Analysis of the stress relaxation data of sulfur‐cured EPDM in nitrogen indicated the presence of stable mono‐ and disulfide linkages and that the main relaxation process resulted from an interchange reaction between polysulfide linkages. In air, in addition to the interchange reaction, oxidative cleavage of mono and disulfide linkages occurred. Further, the stress relaxation for peroxide–sulfurcured EPDM polymers containing various amount of sulfur was observed in air and nitrogen and was discussed in the connection with highly crosslinked polymers.

Stress Softening in Natural Rubber Vulcanizates III. Carbon Black Filled Vulcanizates

Abstract This paper has confirmed the conclusions of the previous paper that the stress softening (Mullins effect) of a black-loaded vulcanizate is similar in magnitude to the stress softening of a gum rubber if the two vulcanizates are stretched initially to the same stress. The initial stress used in the present work was 180 kg/cm2, which is very near to the breaking stress of these vulcanizates. The similarity of the normalized stress-strain curves for all the vulcanizates, both gum and loaded with 60 phr of different types of black, suggests that the main difference between the stress-strain characteristics of a filled and a pure gum rubber, after the initial stressing cycle, can be accounted for by the strain amplification factor X. The more reinforcing blacks possess the higher X factors, i.e., they stiffen the rubber more than, for example, a fine thermal black. It is concluded that the black is acting mainly in a stiffening capacity due to the hydrodynamic effects of the degenerate carbon black networks. For sulfur crosslinked pure gum vulcanizates, in which the crosslinks are polysulfidic, the stress softening is partly associated with the breakage of polysulfide linkages. These reform in the extended condition and produce a real permanent set, but the major stress softening is attributed to the incomplete recovery of the crosslinked network to its initial random state due to network junctions or similar associations being displaced in a nonaffine way during extension. For example, junctions at the ends of chains which become fully extended at relatively low extensions will be displaced in this way. Thus when the rubber is subsequently strained, the network is already in a preferred disposition.

Effect of Curing Systems on Fatigue of Natural Rubber Vulcanizates

Abstract The fatigue life of natural rubber-HAF black vulcanizates showed maxima when plotted as a function of crosslink concentration as did other properties related to a tearing process such as tensile strength, crack growth, and tear strength. Accelerated-sulfur vulcanizates were superior to peroxide and nonelemental-sulfur cures; this can be attributed to an exchange of polysulfide crosslinks under stress. An effective antioxidant was essential for maximum fatigue resistance. Accelerated-sulfur systems, although having a higher original fatigue life than peroxide or nonelemental-sulfur cures, showed a rapid loss on accelerated aging in air. This would indicate that an oxidative effect was involved. Sulfur group analyses of the flexed samples showed an increase in the concentration of RSSxSR linkages but a decrease in the total polysulfide sulfur, Sx, with no change in the crosslink densities. This suggests that the polysulfide linkages not only underwent exchange during the fatigue process but also homolytic cleavage to polythiyl radicals. These radicals can add to double bonds and in the presence of oxygen initiate oxidation chains which would lead to main chain scission.

Relaxation of Disulfide and Tetrasulfide Polymers

Abstract The chemorheology of crosslinked polyethylene disulfide, polyethylene tetrasulfide, and mixtures of these polymers with elemental sulfur is investigated. It is shown that stress decay in the disulfide polymer occurs by scission of the small quantities of higher polysulfide linkages present in the network. It is also shown that elemental sulfur decreases the chemical relaxation time in crosslinked polyethylene disulfide in a predictable manner.