Sulfide polymers polysulfides

Poly sulfide Polymers. These polymers are made up of aliphatic hydrocarbon units connected by di-, tri- or tetrasulfide links. The synthetic rubber found useful in ordn has hydrocarbon units linked by either O or formal segments. The polymers are usually prepd by the condensation of a suitable organic dihalide, usually the chloride, with aq Na polysulfide. According to Ref 8, the most practical organic dichloride is dichlorodiethylformal viz, Bis[ 2[Pg.827]

Epoxy-polysulfide systems can be formulated either as a liquid DGEBA epoxy mixed with liquid poly sulfide polymer or as an epoxy-terminated polysulfide polymer either may be cured with a tertiary amine such as DMP-30. Table 11.19 describes the formulation and shows the physical properties of these epoxy-polysulfide adhesives compared to an unmodified epoxy adhesive. 

Poly(1,3-phenylene sulfide) also is known and has a decomposition temperature higher than poly(1,4-phenylene sulfide). The same reaction can take place with alkyl dihalides, such as 1,2-dichloroethane. However, since sodium sulfide is very frequently a mixture of sulfide and polysulfides, the polymer structure is better expressed by the formula -(R-Sx-)n- Other reactions are known to lead to polysulfides. For example, poly(phenylene sulfide) can be obtained from 4-chlorothiophenol by self condensation in the presence of a metal base. 

Thiokol A, Eihanite, Perdu ren. The first commercial poly-sulfide polymer, prepd from ethylene dichloride and sodium polysulfide. Sulfur content 84% d about 1.6. Mixes with natural rubber. Cured polymer retains unpleasant odor irritating fumes evolve during manuf. Stable to the usual organic solvents and dil mineral acids. Unstable to alkalies and oxidizing substances. Of low tensile strength and abrasion resistance. Not recommended where tropic or arctic climates prevail,... 

The sulfide polymers covered in this chapter are those based on the polysulfides derived from the reaction of dihalides and sodium di- or polysulfides polyphenylene sulfides generated from aryl dihalides and sodium sulfide polyalkylene sulfides generated from ethylene episulfide or dimercaptan-olefin or diolefin-diketone reactions, all of which are outlined in Scheme 1. 

The sulfide polymers are used because of their resistance to oils and solvents, and they are used as specialty plastics [poly(phenyl sulfides)] or as gaskets, hoses, printing rolls, etc. (polysulfides). 

Polysulfide Sealants. Liquid poly sulfide polymers are the base of poly sulfide sealants, the workhorse elastomeric sealants used in construction, glazing, marine, and aircraft applications for over 35 years. 

Cyclic monomers that have been polymerized via ring-opening encompass a variety of structures, such as alkanes, alkenes, compounds containing heteroatoms in the ring oxygen [ethers, acetals, esters (lactones, lactides, and carbonates), and anhydrides], sulfur (polysulfur, sulfides and polysulfides), nitrogen [amines, amides (lactames), imides, N-carboxyanhydrides and 1,3-oxaza derivatives], phosphorus (phosphates, phosphonates, phosphites, phosphines and phosphazenes), or silicon (siloxanes, silaethers, carbosilanes and silanes). For the majority of these monomers, convenient polymerization conditions have been elaborated, that result in the controlled synthesis of the corresponding polymers [1-13]. 

The polysulfide base material contains 50—80% of the polyfunctional mercaptan, which is a clear, amber, sympy Hquid polymer with a viscosity at 25°C of 35, 000 Pa-s(= cP), an average mol wt of 4000, a pH range of 6—8, and a ntild, characteristic mercaptan odor. Fillers are added to extend, reinforce, harden, and color the base. They may iaclude siUca, calcium sulfate, ziac oxide, ziac sulfide [1314-98-3] alumina, titanium dioxide [13463-67-7] and calcium carbonate. The high shear strength of the Hquid polymer makes the compositions difficult to mix. The addition of limited amounts of diluents improves the mix without reduciag the set-mbber characteristics unduly, eg, dibutyl phthalate [84-74-2], tricresyl phosphate [1330-78-5], and tributyl citrate [77-94-1]. 

The synthesis of polysulfide elastomers involves the use of a small amount of trichloroalkane in addition to dichloroalkane and sodium sulfide in order to form a branched polymer. The prepolymer is treated with a mixture of sodium hydrosulfide and sodium sulfite followed by acidification to convert all end-groups to thiol groups. Further polymerization and crosslinking is achieved by oxidative coupling of the thiol end-groups by treatment with lead dioxide, p-quinone dioxime, or other oxidizing agent... 

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). 

Vulcanization by heating with sulfur alone is a very inefficient process with approximately 40-50 sulfur atoms incorporated into the polymer per crosslink. Sulfur is wasted by the formation of long polysulfide crosslinks (i.e., high values of m in XHI), vicinal crosslinks (XIV), and intramolecular cyclic sulfide structures (XV). (Structures XIV and XV do not contribute significantly to the physical properties of the polymer.)... 

The liquid polymer is converted to the rubbery state by reagents that react with mercaptan (-SH) and side groups of the polymer segments by oxidation, addition or condensation to effect sulfide (-S-S-) bond formation. The oxidation reactions are exothermic and accelerated by an alkaline environment. The most commonly employed oxidizing agents which are suitable for curing liquid polymers are cobalt or manganese or lead octoate, p-quinonedioxime and di- or tri-nitrobenzene. Epoxy resin also reacts with liquid polysulfide polymers by addition in the presence of an aliphatic or aromatic amine and polyamide activator as shown in Equation 5.8 ... 

An important aspect of this is the splitting of the polymer chain with thiol (eq. 5) or mercaptide ion (thiol + base catalyst). In fact, sodium sulfide or oiganic monothiols, eg, mercaptoethanol or decyknercaptan, are utilized to lower the molecular weight of polysulfides or to limit the extent of curing reactions. 

These polymers are typically prepared by reaction of sodium polysulfide with a formal. Bis(2-chloroelhy(formal) is commonly used, but some tn functional chlorinated hydrocarbon with its associated higher functionality is typically also added to promote branching. The sodium poly sulfide is usually made by the direct reaction of sodium hydroxide with sulfur at temperatures near 120 °C, as shown in reaction (9) 62... 

Table 11.18 shows the effect of increasing the poly sulfide-epoxy ratio on impact properties the effect at concentrations of polysulfide polymer greater than 1 1 is especially significant. The combination of increased flexibility, tensile strength, and elongation is very desirable in certain adhesive applications. 

A patent (6) assigned to the Societe Nationale des Petroles d Aqui-taine covers the use of, for example, a polymer made by the interaction of epichlorohydrin, hydrogen sulfide, and alkali or alkaline earth polysulfide in aqueous solution. This polymer, HS—[CH2—CHOH—CH2— S]nH where n = 4-24, is mixed with elemental sulfur, a polyolefin (e.g. polybutene), and an olefin (e.g. styrene). This type of mixture, after heating at 140-160 °C, has been used for traffic striping and is said to be serviceable without flaking after 1 years use, despite heavy traffic. 

As is true for most rubbers, the physical properties of cured polysulfide polymers are poor unless reinforcing fillers are used. The semireinforcing blacks are best, and are the main fillers usually employed. Zinc sulfide, titanium dioxide, calcium carbo nate, and lithopone all are useful for reinforcing white or light stocks. In general, the same fillers are used in polysulfide rubbers aa in the other ssnathetic rubbers. 

Swaab and Sutker [24] reported a modification of the foregoing procedure in which a solid, particulate, polysulfide polymer mixture is formed that is free flowing, insensitive to moisture, and redispersible in water to form a stable latex. The process involves the reaction of a Bimte salt (reaction product of sodium thiosulfate and bis(chloroethyl) ether with calcium sulfide in the presence of 5-30% of a dispersing agent [Mg(OH)2 or the sodium salt of a polyalkyl-naphthalenesulfonic acid]. 

The poly(alkylene sulfides) are aliphatic polymers with a single sulfur atom as a repeat group (—RS—) in contrast to the polysulfides which have one or more sulfe atom repeat-group combinations (—R—) where x is 2 or more units. The poly(alkylene sulfides) have quite different properties in comparison... 

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