Polysulfide compounding

Although belonging to a slightly different class of reactions, the reaction of trifluoromethyl radicals with sulfur vapor has been shown to provide a route to trifluoromethyl polysulfide compounds (20). Instead of using sulfur halides, which undoubtedly would also give positive results, elemental sulfur (Ss) was vaporized and dissociated into atomic and polyatomic sulfur species. 

The action of zinc in increasing the efficiency and rate of crosslinking is thought to involve chelation of zinc with the accelerator as well as species XVIII and XIX. Zinc polysulfide compounds such as XX are also likely intermediates. Zinc chelated to sulfur or as zinc sulfide bonds probably facilitate cleavage of sulfur-sulfur bonds in the concerted reactions described by Eqs. 9-20 and 9-21. 

The structures of nine of these compounds were determined by spectroscopic methods, while those of the 14 remaining materials were established by GC-MS only. The compounds can be classified into four types (A to D) the 1,2,4-trithiolanes (145-154), 1,2,4,5-tetrathianes (155-157), 1,2,3,5,6-pentathiepanes (158-163), which are all generally quite stable compounds, and the monoalkyl-substituted polysulfides (164-167), which tend to disproportionate into sulfur and disubstituted cyclic polysulfides. These compounds are structurally related to the cyclic polysulfide compounds reported from red alga Chondria californica in 1976 [136] and to compound 168 (3-hexyl-4,5-dithiacycloheptanone) reported from the brown algae of the Dictyopteris genus in 1971 [137]. The latter compound has more recently been found to be a potent inhibitor of bee venom-derived phospholipase A2 (PLA2) [138]. 

Luther III, G.W. (1991) Pyrite synthesis via polysulfide compounds. Geochim. Cosmochim. Acta 55, 2839-2849. 

The presulfided catalyst used in this study was industrially prepared of a commercial CoMo type HDS catalyst by the Sulficat Process, impregnation with an organic polysulfide compound followed by fixation at an elevated temperature. The amount of sulfur introduced on the catalyst has been calculated from the theoretical stoechiometry necessary to convert all the molybdenum and cobalt into M0S2 and CoqSg. 

Carbon Blacks - Two classes of carbon blacks most frequently used in compounding liquid polysulfide polymers are the furnace and thermal blacks. SRF 3 and Sterling MT are fillers typical of these two classes of carbon blacks. Channel blacks are not used in polysulfide compounds. Their low pH considerably retards the rate of cure and the very large surface area greatly restricts volume loading. 

Clays - Most commercial clays are classified as hydrous. They are undesirable for use in liquid polysulfide base compounds because of their low pH. However, calcined clays have been found to be satisfactory for use in polysulfide compounds because they are less acidic. The best use of calcined clay fillers is in conjunction with precipitated calcium carbonate fillers to produce a compound with a relatively neutral pH value. For example, calcined clay of the type similar to Icecap K has given good results. 

Mineral and Black Fillers for LP Liquid Polysulfide Compounds... 

Titanium dioxide fillers of the rutile type are considerably better for polysulfide compounds than fillers of the anatase type. Titanium dioxide is generally used to impart whiteness or give better color stability to light colored compounds. These fillers, represented by Titanox 2020, are preferred for use in polysulfide compounds. Generally, the level for loading is in the range of 10 to 25 parts. 

Other fillers which have been found to be satisfactory for use in polysulfide compounds are zinc sulfide, lithopone and barium sulfate. These fillers have the highest specific gravity and are higher in cost, but have been used in special compounds for dental impression and cold molding applications. 

The amount or type of plasticizer used must be compatible in the cured sealant and its volatility should be adequate for its intended use. Table V and FIGURE 4 show the effect of three typical plasticizers on the properties of a polysulfide compound. 

Sulfur in some polysulfide compounds has a significant effect on the cure rate (Table VII) generally resulting in tougher, more resilient materials since the sulfur converts metal mercaptides to disulfide linkages. 

Organic polysulfide compounds, with the general formula R2SX+3, which limit the irreversible deposition of Li2S on the metal lithium electrode The compound Li2S reacts with R2S c+y according to the reaction ... 

Extmsion of polysulfide compounds should be done in as large a tuber as available to obtain maximum head pressure. The screw and barrel needs to be at 37°C 8°C with the head temperature a bit higher and the die hot The stock should be fed in steady, small, thin strips, taking care not to allow the compound to back up in the throat and choke the feed. The feedstock should not be warmed on a cool mill as sticking to the roll surface may occur. 

Variations in the viscosity of FA polysulfide compounds may be attributed to either inaccurate weighing of the MBTS and DPG or to a loss of these materials through inefficient sweeping during the mix. In addition, insufficient time or temperature on the null may not have allowed for complete softening of the polymer. 

The data are presented in Table IX on the reaction of sulfite and cyanide ions with various polysulfide compounds. The results show that (1) the shorter the bond the higher the activation energy, (2) the difference between the Ea values for sulfite and cyanide decreases slightly as the bond becomes longer, and (3) the relationship seems to hold even though several different charge-type reactions are represented. 

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