Polysulfide fractions

This chapter reports the study of the chemical composition of the polysulfide fraction in dicyclopentadiene and styrene modified materials, the mechanical properties of modified materials, and their use in the preparation of composite materials by the impregnation of polypropylene and glass-fiber fabrics. 

Aging of these materials in addition to changes in sulfur crystallinity may involve changes in the nature of the polysulfide fractions. For example, one styrene polysulfide has an average sulfur rank of 6.75. This is extremely high, and it can be expected to be very unstable. Tetra-sulfides and above are unstable and decompose, forming polysulfides with lower sulfur rank and elemental sulfur. Future work will explore this possibility. 

Examination of Polysulfide Fractions. Polysulfide fractions from the alloocimene, myrcene, limonene, styrene, and Thiokol LP-33 materials prepared at 140 °C have been fractionated by gel permeation chromatography. Other Thiokol products could not be examined because they were insoluble in all organic solvents used. In Tables VIII-XII the molecular weight and molecular formula of each fraction are given. Table... 

Table XIII. Analysis of Principal Polysulfide Fractions...

C2h isomer (8) is less well characterized but is said to result from the reaction of hexachlorobutadiene, CCI2 =CC1—CCl=CCl2, with polysulfide anions. The treatment of S2CI2 with [NBu4]2[Zn(o -C3S5)2] yields a mixture of C3Sg and C6S12 which can be separated by fractional crystallization from CS2 ... 

It has been illustrated that polycrystalline materials can be operated in regenerative electrolytic solar cells yielding substantial fractions of the respectable energy conversion efficiency obtained by using single crystals. Pressure-sintered electrodes of CdSe subsequently doped with Cd vapor have presented solar conversion efficiencies approaching 3/4 of those exhibited by single-crystal CdSe electrodes in alkaline polysulfide PEC [84]. 

Fig. 10. Compression stress-strain properties of various elastomeric syntactic foams129> (l)urethane elastomer binder and glass microspheres y = 640 kg/m3, void fraction 0.321 (2) polysulfide elastomer binder and phenolic microspheres y = 1500 kg/m3, void fraction 0.133 (3) silicone elastomer binder and glass microspheres y = 610 kg/m3, void fraction 0.407...

Bacterially produced elemental sulfur can also react with hydrogen sulfide form polysulnde ions. Thus, polysulfide ions should constitute a significant fraction of sulfur nudeophiles in reducing sediments especially where sulfide oxidation is incomplete, such as in intertidal and salt marsh sediments (31321. The polysulfide ions should also be important at redox boundaries (anoxic/ suboxic) in the water column of marine anoxic basins, such as the Black Sea. 

The average concentrations of reduced inorganic sulfur species in the anoxic zone of the Black Sea measured using a new colorimetric method developed by Volkov [61,62] are summarized in Table 3. Presented elemental sulfur data refer to the stun of elemental sulfur allotropes (zero-valent sulfur) and the zero-valent sulfur derived from some fraction (n - 1) of the original polysulfide S 2. Thiosulfate data in the table represent the total amount of thiosulfate, sulfite, and polythionates. At some stations in the Black Sea, Volkov [61] observed a concentration maximum of elemental sulfur at the oxic/anoxic interface associated with sulfide oxidation by dissolved oxygen and/or Mn oxyhydroxides. Increasing with depth, elemental sulfur concentrations are probably explained by the ongoing process of polysulfide formation... 

It is possible that this polymer is formed by ring-opening polymerization of the cyclic pentasulfide or other cyclic polysulfides. In a separate experiment, heating the trisulfide gave a similar chain polymer. We have not been able to separate the fraction VRE = 0.72 which was formed in much smaller quantities than other fractions. 

All the other reaction products appear to be chain styrene polysulfides of different molecular weights. The two oligomers I and II have been obtained from the fraction VRE approx. 0.73, and fully characterized by elemental analysis, molecular weight measurement, and various spectroscopic techniques. 

Liquid sulfur-dicyclopentadiene (DCP) solutions at 140°C undergo bulk copolymerization where the melt viscosity and surface tension of the solutions increase with time. A general melt viscosity equation rj == tj0 exp(aXH), at constant temperature, has been developed, where tj is the viscosity at time t for an S -DCP feed composition of DCP mole fraction X and rj0 (in viscosity units), a (in time 1), and b (a dimensionless number, -f- ve for X < 0.5 and —ve for X > 0.5) are empirical constants. The structure of the sul-furated products has been analyzed by NMR. Sulfur non-crystallizable copolymeric compositions have been obtained as shown by thermal analysis (DSC). Dodecyl polysulfide is a viscosity suppressor and a plasticizer for the S8-DCP system. 

Aqueous polysulfide solutions give, upon acidification, a erode oil that, from Raman spectroscopy, contains a range of polysulfanes (H2S, x = 2-6) x = 2 and 3 species are obtained from this oil by careful distillation/cracking of the mixture. The products can then be purified further by fractional distillation. 

This situation is reversed in the case of ENB-EPDM (Table 17) since, after high vulcanization times, relevant fractions of polysulfidic and disulfidic links are still present, while the overall cross-link density is rather low in relation with the unsaturation content. 

Symmetrical disulfides (73) may be prepared by reaction of alkyl halides with disodium disulfide (Scheme 43). The product is contaminated with triand polysulfides owing to the presence of impurities in the disodium disulfide however, lower members of the series of dialkyl disulfides may be purified by fractional distillation. Disulfides can also be obtained from thiols by mild oxidation, e.g. by treatment with iodine or dimethyl sulfoxide (DMSO) (Scheme 44). In the reaction with iodine, the hydriodic acid formed must be removed, otherwise the disulfide is largely reduced back to the thiol by hydriodic acid which is a powerful reducing agent. Pure unsymmetrical disulfides are more difficult to prepare owing to their tendency to undergo disproportionation they can, however, be synthesised from thiols by treatment with imides (see p. 59) or sulfenyl halides (51) (Scheme 45). 

Disulfides and polysulfides are useful for sulfiding hydrotreating catalysts, used in petroleum refining to convert metal oxides to the preferred metal sulfides. Hydrotreating is an essential process in the refining of petroleum. It removes heteroatoms, nitrogen, and sulfur from crude oil and its fractions, formulated into gasoline and diesel (Table 5). 

Since the aqueous sodium polysulfide contains already several polysulfide anions in equilibrium and since the acidification results in some interconversion reactions, a sulfane mixture H2S c is obtained rather than pure H2S4. This mixture nevertheless reacts in dry CS2/Et20 mixture at 20 °C with dichlorodisulfane, besides other products, to S12 which has been isolated in 4% yield by extraction with CS2 and fractional crystallization [41] ... 

I. From molybdenite, the extraction may be made in several ways, (a) The mineral is roasted as long as sulfur dioxide is given off. The residue which contains MoOs is leached with dilute ammonia and the solution evaporated until the ammonium molybdate crystallizes. Japanese patent 37420 (1920) extracts the roasted ore with Na2COj solution, then precipitates calcium molybdate by adding CaCb. (6) The finely ground ore is heated with nitric acid and the MoOj dissolved in ammonia, (c) A current of chlorine is passed over the dry pulverized ore at a temperature of 208°. The molybdenum chloride distills over and may be separated from sulfur and other chlorides by fractional condensation.2 (d) A British patent describes the extraction with an alkaline sulfide or polysulfide solution which removes the molybdenum from the ore as the soluble thio-molybdates. These may be converted to the molybdates by acidification or by contact with more ore. 

Polysulfanes are compounds of the general type H2S, where x>2 (see structure 15.6). Sulfur dissolves in aqueous solutions of group 1 or 2 metal sulfides (e.g. Na2S) to yield polysulfide salts, (e.g. Na2S, ). Acidification of such solutions gives a mixture of polysulfanes as a yellow oil, which can be fractionally distilled to yield H2S c (x = 2-6). An alternative method of synthesis, particularly useful for polysulfanes with X > 6, is by condensation reaction 15.40. 

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