Sulfur-Containing Oligomers

Synthesized as early as 1943 [1], polysulfide oligomers (PSOs) soon became rather important raw materials for producing sealant compositions. Ten years later, Thi-okol Chemical Corp. produced them industrially, and in the Soviet Union, a team of research workers led by Apukhtina elaborated a technology of their own (2,31. At present, developed countries produce important quantities of PSOs. There are also data on production capacities in other countries, such as Poland and Romania the latter in fact has its own technology [4-6]. 

Most industrial PSOs have a low branched structure with final SH groups in keeping with the following formula  

Polysulfide sealants have found wide acceptance in construction, aircraft, automotive, marine, and insulating glass. In fact, polysulfide sealants were the first elastomeric sealants used in the construction industry and continue today, to a large extent, to be the standard with which other sealants are compared. 

Polysulfide sealants, although facing strong challenges from silicones and polyurethanes, continue to be the dominant segment of the elastomeric sealant market (Table 1) [2], 

Several methods of synthesizing oligosulfides are known degradation of polysulfides with high molecular mass by means of Bunte Salts, or radical polymerization of olefins or dienes in the presence of sulfur. Oligosulfides can also be obtained by polymerization of thiiranes and by oxidation of low molecular weight dimercaptanes. 

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Bauerle, P. (1998) Sulfur-containing oligomers, in Electronic Materials The Oligomer Approach (eds K. Mullen and G. Wegner), Wiley-VCH Verlag GmbH, Weinheim, pp. 105—197. 

Another method of obtaining sulfur-containing oligomers and polymers is thiirane polymerization. In the presence of proton donors (e.g., H2S and ditiols), thiiranes polymerize with the formation of polythyolesterditiols. 

Several sulfur-containing /3-peptide analogues have been generated (Figure 42). Oligomers in which the peptide bond has been replaced by the sulfonamide (i.e., /3-sulfonopeptides),306-309 sulfinamide (i.e., /3-sulfi-... 

In other investigations, several cyclic sulfides were foimd to be present in the corresponding sulfur-containing polymers, and FAB-MS allowed the identification of all the oligomers resolved in the SEC traces. ... 

FIGURE 1 Schematic models of chlorosomes from the green gliding bacteria, e.g. Chloroflexus aurantiacus (A) and the green sulfur bacteria, e.g. Chlorobium vibrioforme (B). The numbers refer to wavelength maxima of antenna bacteriochlorophyll complexes. The reaction centers are of the "quinone type in A, with a QA Qb acceptor complex and the Fe-S type in B, with Fe-S proteins as early electron acceptors. The rod elements probably contain oligomers of bacteriochlorophyll c, d or e, as discussed in Ae text. 

Tsukube, H., Nakamura, A., and Maruyama, K. Synthesis and metal binding properties of novel sulfur-containing functional oligomer, J. Polymer Sci., Polym. Chem. Ed., 18, 1359, 1980. 

Cmde diketene obtained from the dimeriza tion of ketene is dark brown and contains up to 10% higher ketene oligomers but can be used without further purification. In the cmde form, however, diketene has only limited stabHity. Therefore, especiaHy if it has to be stored for some time, the cmde diketene is distiHed to > 99.5% purity (124). The tarry distiHation residue, containing trike ten e (5) and other oligomers, tends to undergo violent Spontaneous decomposition and is neutralized immediately with water or a low alcohol. Ultrapure diketene (99.99%) can be obtained by crystallization (125,126). Diketene can be stabHized to some extent with agents such as alcohols and even smaH quantities of water [7732-18-5] (127), phenols, boron oxides, sulfur [7704-34-9] (128) and sulfate salts, eg, anhydrous copper sulfate [7758-98-7]. 

Sulfur Polymer Cement. SPC has been proven effective in reducing leach rates of reactive heavy metals to the extent that some wastes can be managed solely as low level waste (LLW). When SPC is combined with mercury and lead oxides (both toxic metals), it interacts chemically to form mercury sulfide, HgS, and lead sulfide, PbS, both of which are insoluble in water. A dried sulfur residue from petroleum refining that contained 600-ppm vanadium (a carcinogen) was chemically modified using dicyclopentadiene and oligomer of cyclopentadiene and used to make SC (58). This material was examined by the California Department of Health Services (Cal EPA) and the leachable level of vanadium had been reduced to 8.3 ppm, well below the soluble threshold limit concentration of 24 ppm (59). 

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