Poly sulfide processing

N. Anastasijevic The name of Dr. Anastasijevic is associated both to the first NEMCA study in liquids (Chapter 10), together with Baltruschat and Heitbaum, but also with the development at LURGI of a new NEMCA-based process for the production of ammonium poly sulfide (Chapter 10). Chronologically he was the first aqueous electrochemist who realized the importance and potential of NEMCA. 

Sealants obtained by curing polysulfide liquid polymers with aryl bis(nitrile oxides) possess stmctural feature of thiohydroximic acid ester. These materials exhibit poor thermal stability when heated at 60°C they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degrade faster than those produced with equimolar amounts of reagents. Spectroscopic studies demonstrate that, after an initial rapid addition between nitrile oxide and thiol, a second slower reaction occurs which consumes additional nitrile oxide. Thiohydroximic acid derivatives have been shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol. In the case of a polysulfide sealant, the rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process leads to degradation of the sealant. These observations have been supported by thermal analysis studies on the poly sulfide sealants and model polymers (511). 

In the polysulfide bake process, the starting materials are first steam-treated with aqueous sodium poly sulfide solution the thickened mass is then heated to above 180 °C. In a first reaction step, the nitro groups, if present, are reduced to amino groups. 

Formate dehydrogenase and poly sulfide reductase function by what could be called simple CEPT (see Section VI.B.2). However, if CEPT is an important component of substrate reactivity in most of the molybdenum and tungsten enzymes, it must involve not only substrate activation but also water addition or elimination. Involvement of the metal in these processes could rely on oxidation state-coupled pA a changes of aqua, hydroxido, or hydrosulfido ligands. Whether the metal is directly involved in substrate binding and water activation or whether... 

Poly sulfide compounds that are compatible with epoxy resins are liquid elastomers at room temperature. The most significant commercial resin of this type is LP-3 from Toray. The predominant product is a mercaptan-terminated liquid polymer (LP) that contains approximately 37% bound sulfur (see Fig. 7.2). It is the high concentration of sulfur linkages that provides these products with their unique chemical properties. A sulfur odor is noticeable during processing, making ventilation important. 

The hydrothermal method has been used to prepare monodispersed ZnS (6 nm) [10] and CdS nanocrystals (16 nm) [11]. By hydrothermal polymerization and simultaneous sulfidation processes, nanocomposites CdS/poly(vinyl acetate) nanorods [12] and nanospheres [13] were synthesized. In aqueous hydrazine solutions, nonstoichiometric metal telluride nanocrystallites such as Cu2.86Te2, CuyTes, Cuy-xTe, and Ag7Te4 [14], and cubic CogSg were hydrothermally synthesized [15]. Other transition metal chalcogenides, such as single-molecular-layer M0S2 [16] and MoSey [17] were also prepared under hydrothermal conditions. 

In the polymerization of propylene sulfide and 1,2-butylene sulfide mainly tetra-mers were observed. Cycles were formed mostly during the slow degradation process that followed rapid polymerizations. Degradation can also be induced by adding cationic initiators to polymer prepared by other mechanisms, e.g. by anionic processes. Thus, poly(trans-2,3-butene sulfide) is rapidly degraded to equimolar amounts of 3,5,6,7-tetramethyl-l,2,5-trithiacycloheptane and trans-butene 47). Poly(cis-2,3-butene sulfide) forms, however, a mixture of tetramer, trithiacycloheptane derivative and cis-butene 47 . If one is forced to use cationic processes for the synthesis of poly-sulfides, the reaction conditions should be controlled to avoid macrocyclization. If cyclic products are desired, the kinetics of their formation should be studied to determine optimum yields. 

Thiosulfate process for making organic poly sulfides [140]. 

Amine activating agents added in the process of peroxidic curing of poly-sulfidic oligomers are introduced directly into the system, before peroxide or hydroperoxide introduction. The mechanism of aminic compounds action is based on the formation of ion radicals, in keeping with the following reactions ... 

Comparing the process of electrochemical activation to standard base-promoted addition of sulfur, the ylidene sulfur adduct 12 is formed by addition of a S -cyanomethyl anion onto t ano group (Scheme 9), while in the previous version the poly sulfide-like anion affects the methylene group of the a,p-unsaturated nitrile 10 (Scheme 8). However, if the activation with sulfur does not occur properly, the ylidene-sulfur adduct of presumed structure 10 or 12 is not formed and the side-reaction takes place. 

Poly sulfides were first discovered and patented in about 1927 by J.C. Patrick by accident in attempting to develop antifreeze. The polymer was called Thiokol A, a condensation reaction of ethylene dichloride and sodium tetrasulfide, for which manufacturing began in 1929 [1]. This elastomer was quite difficult to process due to its variability and thermoplastic nature, leading to the discontinuation of manufacture after improved grades were developed. 

Acrylic ESTER POLYMERS Acrylonitrile POLYMERS Cellulose esters). Engineering plastics (qv) such as acetal resins (qv), polyamides (qv), polycarbonate (qv), polyesters (qv), and poly(phenylene sulfide), and advanced materials such as Hquid crystal polymers, polysulfone, and polyetheretherketone are used in high performance appHcations they are processed at higher temperatures than their commodity counterparts (see Polymers containing sulfur). 

Bayer marketed PPS compounds in the United States under the trade name Tedur, but the company has exited the PPS business. PPS is also marketed in the United States by GE Plastics, whose source of neat resin is Tosoh Corporation of Japan. GE Plastics markets PPS under the trade name Supec PPS. Patent activity by Tennessee Eastman describes an alternative process for the production of poly(phenylene sulfide/disulfide), although samples of such product have not appeared as of early 1996. Both Phillips and Hoechst Celanese have aimounced plans to debotdeneck their existing U.S. faciUties in order to meet anticipated market growth. 

The Eastman Chemical Company has pubHshed extensively in the patent Hterature (65—74) and the scientific Hterature (75—77) on processes for making poly(phenylene sulfide)- (9-(phenylene disulfide), and related copolymers. The Eastman process involves the reaction of elemental sulfur with Ndiiodobenzene to yield a phenylene sulfide polymer that also contains phenylene disulfide repeating units in the polymer. The fraction of repeating groups containing... 

The synthesis of poly(arylene sulfide)s via the thermolysis of bis(4-iodophenyl) disulfide has been reported (78). The process leads to the formation of PPS and elemental iodine. This process presumably occurs analogously to that reported by Eastman Chemical Company. 

In another process for the synthesis of PPS, as well as other poly(arylene sulfide)s and poly(arylene oxide)s, a pentamethylcyclopentadienylmthenium(I) TT-complex is used to activate -dichlorobenzene toward displacement by a variety of nucleophilic comonomers (92). Important facets of this approach, which allow the polymerization to proceed under mild conditions, are the tremendous activation afforded by the TT-coordinated transition-metal group and the improved solubiUty of the resultant organometaUic derivative of PPS. Decomplexation of the organometaUic derivative polymers may, however, be compHcated by precipitation of the polymer after partial decomplexation. 

Common conductive polymers are poly acetylene, polyphenylene, poly-(phenylene sulfide), polypyrrole, and polyvinylcarba2ole (123) (see Electrically conductive polymers). A static-dissipative polymer based on a polyether copolymer has been aimounced (124). In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibiUty. Conductive polymers have met with limited commercial success. 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

Some of the common types of plastics that ate used ate thermoplastics, such as poly(phenylene sulfide) (PPS) (see Polymers containing sulfur), nylons, Hquid crystal polymer (LCP), the polyesters (qv) such as polyesters that ate 30% glass-fiber reinforced, and poly(ethylene terephthalate) (PET), and polyetherimide (PEI) and thermosets such as diaHyl phthalate and phenoHc resins (qv). Because of the wide variety of manufacturing processes and usage requirements, these materials ate available in several variations which have a range of physical properties. 

Montaudo and co-workers have used direct pyrolysis mass spectrometry (DPMS) to analyse the high-temperature (>500°C) pyrolysis compounds evolved from several condensation polymers, including poly(bisphenol-A-carbonate) [69], poly(ether sulfone) (PES) and poly(phenylene oxide) (PPO) [72] and poly(phenylene sulfide) (PPS) [73]. Additionally, in order to obtain data on the involatile charred residue formed during the isothermal pyrolysis process, the pyrolysis residue was subjected to aminolysis, and then the aminolyzed residue analysed using fast atom bombardment (FAB) MS. During the DPMS measurements, EI-MS scans were made every 3 s continuously over the mass range 10-1,000 Da with an interscan time of 3 s. 

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