Polysulfide specifications

AU products Usted have flash point (PMCC) > 177°C. The specific gravity at 25°C ranges from 1.27 to 1.31. CAS Registry Number for aU the LPs Usted is [68611-50-7] ie, they are copolymers made from (3) and 1,2,3-trichloropropane, and sodium polysulfide. 

Typical specifications for the polysulfide polymers are summarized in Table 1. Specifications for the sealants vary widely depending on the specific apphcation and the needs of the appHcators. Standards for sealant testing vary in different countries. Ultimately, the tests should simulate the environment the sealants will be exposed to and measure their performance under these conditions. 

Wea.ther lbillty. One of the more destmctive elements is exposure to sunlight specifically, ultraviolet (uv) light. AH sealants are affected by weathering, but there is much difference in the effect of weathering on different sealants. Most sHicones are stable with respect to uv exposure. Urethanes and polysulfides show effects of uv exposure, but can be formulated with uv absorbers to provide reasonable lifetimes in most appHcations. However, there are exceptions in aH classes of sealants and specifiers must be carehil to look for test data that has proven a specific sealant s durabHity. The source of the test data is also important data from an independent testing laboratory is generaHy apt to be more reHable. 

Monomer conversion (79) is followed by measuring the specific gravity of the emulsion. The polymerization is stopped at 91% conversion (sp gr 1.069) by adding a xylene solution of tetraethylthiuram disulfide. The emulsion is cooled to 20°C and aged at this temperature for about 8 hours to peptize the polymer. During this process, the disulfide reacts with and cleaves polysulfide chain segments. Thiuram disulfide also serves to retard formation of gel polymer in the finished dry product. After aging, the alkaline latex is acidified to pH 5.5—5.8 with 10% acetic acid. This effectively stops the peptization reaction and neutralizes the rosin soap (80). 

Importantly, Licht [104], using the optimized polysulfide elecfrolyfes developed for CdX PEC (described in a preceding paragraph), was able fo demonsfrafe frue long-term stability for a polycrystalline pasted thin film Cd(Se,Te)/aqueous polysulfide system. In specific, complete stability was exhibited for an 8-month outdoors operation at 4.1% conversion efficiency. 

The photoelectrochemical behavior of ZnSe-coated CdSe thin Aims (both deposited by vacuum evaporation on Ti) in polysulflde solution has been described by Russak and Reichman [112] and was reported to be similar to MIS-type devices. Specifically, Auger depth profiling showed the ZnSe component of the (ZnSe)CdSe heterostructures to convert to ZnO after heat treatment in air, thus forming a (ZnO)CdSe structure, while the ZnO surface layer was further converted to a ZnS layer by cycling the electrode in polysulfide electrolyte. This electrochemically generated ZnS layer provided an enhanced open-circuit potential compared to CdSe alone. Efficiencies as high as 5.4% under simulated AM2 conditions were recorded for these electrodes. 

Polymerizations are classified as either step (condensation) or chain (addition) polymerizations. The two differ in the time-scale of various reaction events, specifically in the length of time required for the growth of large-sized molecules. The synthesis of polysulfides (Eq. 1) and polyurethanes (Eq. 2) are... 

Only the inorganic polysulfides (and more specifically the alkali polysulfides) will be considered. Furthermore, we shall not review the electrochemical properties of SxOy ions or molecules. It must be noted that a comprehensive review, devoted to the oxidation of sulfur(IV) oxides, oriented toward the atmospherically relevant processes and mechanisms, appeared in 1995... 

These examples convincingly demonstrate that specific OSC are formed during the early stages of diagenesis by reactions of reduced sulfur species with specific biogenic substrates. The reactive substrates are proposed to contain either carbon-carbon double bonds or other reactive functional groups that react with either hydrogen sulfide or polysulfides to form the OSC (88). These views are consistent with evidence from sulfur isotopes that H2S produced by microbial sulfate reduction is the major source of reduced sulfur in sediments... 

Of the stabilization methods, the polysulfide pulping process is of practical importance. The influence of polysulfides is based on a specific oxidation of the end groups to carboxyl groups via glucosone intermediates (cf. Section 8.1.3). Polysulfides can be prepared by catalytic oxidation of sulfide in the white liquor or by adding elemental sulfur into the kraft cooking liquor ... 

Table 1, but specifically thiosulfate (8203 ), sulfite (SOa ), polysulfides (Sx ), and elemental sulfur (Saq, which also occurs in the solid phase). The presence of this spectrum of sulfur species and their cyclic interconversion in a redox gradient (such as is present in organic-matter-bearing marine sediments with oxygenated depositional waters) were recognized long ago by Bass Becking (1925) (see also Truper, 1982). 

The soHcalled a nomenclature can also be extended to aliphatic compounds. Here again lack of specific rules prevents a useful application of this system of nomenclature. One of the perplexing problems of a nomenclature is to define the limits for its application. It is a very useful system for naming unsymmetrical polyethers, polysulfides, and polyamines. Thus 3,5,8,12-tetraoxatetradecane is in many respects a better name than l-(ethoxymethoxy)-2-(3-ethoxypropoxy) ethane for... 

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