Polymeric acid disulfides

The use of chain transfer agents in emulsion polymerization was briefly discussed in Sect. 2.2.1. As stated, the most commonly used chain transfer agents are the mer-captans (thioalcohols) RSH, although a wide range of other compounds also exert a modifying effect during polymerization, for example carbon tetrachloride, certain disulfides, rosin acid salts, 4-vinylcyclohexene (butadiene dimer) amongst many others, which may also include impurities in other raw materials. 

Quantitatively, sulfur in a free or combined state is generally determined by oxidizing it to a soluble sulfate, by fusion with an alkaH carbonate if necessary, and precipitating it as insoluble barium sulfate. Oxidation can be effected with such agents as concentrated or fuming nitric acid, bromine, sodium peroxide, potassium nitrate, or potassium chlorate. Free sulfur is normally determined by solution in carbon disulfide, the latter being distilled from the extract. This method is not useful if the sample contains polymeric sulfur. 

C2S2, is a red Hquid (mp —0.5° C, bp 60—70°C at 1.6 kPa (12 mm Hg)) produced by the action of an electric arc on carbon disulfide (1 4). The stmcture has been shown to be S=C=C=C=S on the basis of its reactions to form malonic acid derivatives and on the basis of physical measurements. It is unstable and decomposes ia a few weeks at room temperature it decomposes explosively when heated rapidly at 100—120°C with formation of a black polymeric substance (C2S2) (5,6). Dilute solutions ia CS2 are fairly stable, but photochemical polymerisation to (C2S2) occurs. 

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). 

Trimethylsilyl esters of tris(thio)phosphonic acids 2070 are readily oxidized by DMSO in toluene at -30 °C to give the dimeric tetra(thia)diaphosphorinanes 2071 and HMDSO 7 [208] (cf. also the oxidation of silylated thiophenol via 2055 to diphenyl disulfide). The polymeric Se02 is depolymerized and activated by reaction with trimethylsilyl polyphosphate 195 to give the corresponding modified polymer... 

To further exploit the potential usefiilness of this new family of clusters, monoadduct 54 was saponified into 55 (0.05 M NaOH, quant) and condensed to L-lysine methyl ester using 2-ethoxy-l-ethoxycarbonyl-l,2-dihydroquinoline (EEDQ) to give extended dimer 56 in 50 % yield together with monoadduct in 15 % yield [75]. Additionally, tert-butyl thioethers 52 could be transformed into thiols by a two step process involving 2-nitrobenzenesulfenyl chloride (2-N02-PhSCl, HOAc, r.t, 3h, 84%) followed by disulfide reduction with 2-mercaptoethanol (60%). Curiously, attempts to directly obtain these thiolated telomers by reaction with thioacetic acid f ed. These telomers were slightly better ligands then lactose in inhibition of binding of peanut lectin to a polymeric lactoside [76]. 

Proteins, peptides, and other polymeric macromolecules display varying degrees of chemical and physical stability. The degree of stability of these macromolecules influence the way they are manufactured, distributed, and administered. Chemical stability refers to how readily the molecule can undergo chemical reactions that modify specific amino-acid residues, the building blocks of the proteins and peptides. Chemical instability mechanisms of proteins and peptides include hydrolysis, deamidation, racemization, beta-elimination, disulfide exchange, and oxidation. Physical stability refers to how readily the molecule loses its tertiary and/or sec-... 

In nature, mammalian antibodies occur in five distinct classes IgG, IgA, IgM, IgD, and IgE. These differ in structure, size, amino acid composition, charge, and carbohydrate components. The basic structure of each of the classes of immunoglobulins consists of two identical polypeptide chains linked by disulfide bonds to two identical heavy chains. Differences between classes and subclasses are determined by the makeup of the respective heavy chains. IgG is the major serum immunoglobulin and occurs as a single molecule IgA also occurs as a single molecule but also polymerizes, primarily as a dimer and also associates with a separate protein when secreted. IgM occurs in the serum as a pentamer, with monomers linked by disulfide bonds and the inclusion of an additional polypeptide component, the J-chain. IgD and IgE occur primarily as membrane-bound monomers on -cells, or basophils and mast cells, respectively. 

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