Polysulfides curing

Sealants - [ELASTOMERSSYNTHETIC - POLYISOPRENE] (Vol 9) - [SEALANTS] (Vol 21) -acrylics [ACRYLICESTERPOLYMERS - SURVEY] (Voll) -barium compds in [BARIUM COMPOUNDS] (Vol 3) -based on liquid polysulfides [POLYMERS CONTAINING SULFUR - POLYSULFIDES] (Vol 19) -defoamersin [DEFOAMERS] (Vol 7) -fiom fluorosilicones [FLUORINE COMPOUNDS,ORGANIC - POLY(FLUOROSILICONES)] (Volll) -hydrocarbon resins in [HYDROCARBON RESINS] (Vol 13) -lecithin in (LECITHIN] (Vol 15) -organolithiumcmpdsinprdnof [LITHIUM AND LITHIUM COMPOUNDS] (Vol 15) -polysulfide curing [PEROXIDES AND PEROXIDE COMPOUNDS - INORGANIC PEROXIDES] (Vol 18) -propylene oxide in mfg of [PROPYLENE OXIDE] (Vol 20) -PVB m [VINYL POLYMERS - VINYL ACETAL POLYMERS] (Vol 24) -rheological measurements [RHEOLOGICAL MEASUREMENTS] (Vol 21) -from styrenic block copolymers [ELASTOMERS SYNTHETIC - THERMOPLASTIC ELASTOMERS] (Vol 9) -use of dispersants [DISPERSANTS] (Vol 8)... 

Polysulfides cure at room temperature and reach maximum strength in 3-7 days. Polysulfides and epoxies are mutually soluble in all proportions. Polysulfides are also alloyed with phenolics. ... 

The single-part systems generally require atmospheric moisture to effect cure by inducing oxidation (e.g. single-part polysulfides cured with calcium peroxide) or condensation of a reactive end group as in the case of the polyurethanes and sihcones. The cure mechanisms for these systems can be complicated and depend on a number of factors." ... 

The FA polysulfide rubbers are prepared by reacting a mixture of bis(2-chloroethyl)formal and ethylene dichloride with sodium polysulfide. Cured compounds have exceptionally low permeability to gases, water, and organic liquids and exhibit excellent low-temperature flexibility. The FA polysulfide rubber compounds display excellent resistance to ozone, weathering, and exposure to UV light. In general, their resistance is superior to that of the ST polysulfide rubbers. If high concentrations of ozone are to be present, the use of 0.5 part of NBC per 100 parts FA polysulfide rubber will improve the ozone resistance. 

Epoxy Resins. Polysulftdes may also be cured by reaction with epoxy resins (qv) according to the reaction in equation 2. Amines or other catalysts are used and often primary or secondary amine resins are cured together with the polysulfide. 

Diisocyanates or Polyisocyanates. The thiol end groups of the hquid polysulfides are quite reactive with isocyanates (eq. 3). Typical chisocyanates, such as 1,3-toluene chisocyanate (m-TDl) and diphenylmethane-4,4 -diisocyanate (MDl), ate effective in curing hquid polysulfides. Using hquid polysulfides in-... 

Phenolic Resins. At elevated temperatures, phenoHc resins are cured with polysulfide resins through a condensation reaction. The product may be considered a block copolymer of the rigid phenoHc resin and the flexible polysulfide. Thus, the polysulfide acts to flexibiHze the resulting polymer. 

Miscellaneous Curing Reactions. Other functional groups can react with the thiol terminal groups of the polysulfides to cross-link the polymer chains and build molecular weight. For example, aldehydes can form thioacetals and water. Organic and inorganic acids or esters can form thioesters. Active dienes such as diacrylates can add to the thiols (3). Examples of these have been mentioned in the Hterature, but none have achieved... 

Eig. 8. Sulfiir-based cure system designs where conventional systems are polysulfidic, EV systems are mono-/disulfidic, and semi-EV systems are clean polysulfidic. A shows pendent sulfide groups terminated by accelerator B, monosulftde cross-links C, disulfide cross-links D, polysulftde cross-links... 

Sulfur. Low sulfur stocks and EV sulfur-accelerated systems have better aging resistance. Normally, the oxidation rate increases with the amount of sulfur used in the cure. The increased rate may be due to activation of adjacent C—H groups by high levels of combined sulfur. Saturated sulfides are more inert to oxidation than aHyUc sulfides. Polysulfidic cross-links impart excessive hardening of SBR as compared to more stable monosulfidic cross-links. 

Table 4. Typical One-Part Manganese Dioxide-Cured Polysulfide Formulation ...

Polyurethane sealant formulations use TDI or MDI prepolymers made from polyether polyols. The sealants contain 30—50% of the prepolymer the remainder consists of pigments, fiUers, plastici2ers, adhesion promoters, and other additives. The curing of the sealant is conducted with atmospheric moisture. One-component windshield sealants utili2e diethyl malonate-blocked MDI prepolymers (46). Several polyurethane hybrid systems, containing epoxies, siUcones, or polysulfide, are also used. 

The second catalyst paste of the two-paste product is a curing agent. A wide variety of materials convert the Hquid polysulfide polymers to elastomeric products. Alkalies, sulfur, metallic oxides, metallic peroxides, organic peroxides, and many metal—organic salts, ie, paint driers, are all potential curing agents. 

Many curing systems bring about aHquid—to—soHd conversion of the polysulfide polymers. Most curing agents produce an initial soHd mass characterized by a high degree of plasticity and poor elasticity. The development of elastic properties is so slow that the materials are not suitable for the accurate reproduction of undercut areas found ia oral stmctures. 

Only two types of systems have found appHcation ia dentistry. Lead peroxide is the curing agent most frequently used for the polysulfide polymers that serve as dental impression materials. Lead peroxide converts the Hquid polymer to an elastic soHd within a time short enough for oral appHcations. 

In the presence of the organic siHcate, the heavy-metal salts trigger the chain extension and cross-linking reactions that lead to siHcone mbber and volatile ethanol as a byproduct. Useful metal soaps iaclude stannous octanoate [1912-83-0], ziac octanoate [557-09-5], dibutyltin dilaurate [77-58-7], and dibutyltin diacetate [1067-33-0]. The reactivity of the different salts varies considerably. Stannous octanoate effects a cure ia 0.5—2 min ziac octanoate may require 24—96 h the dibutyltin dilaurate, 10—20 min. Heat and moisture accelerate the curing rate, but to a lesser degree than ia the case of the polysulfide mbbers. 

Although inhibitors are deliberately added to the silicone formulation to control cure rate, unwanted cure inhibition can be caused by other species that react to form strong complexes with the platinum catalyst. Most notable of these undesired inhibitors include organotin and other organometallic compounds, sulfur, polysulfides, polysulfones or other sulfur-containing materials, amines, urethanes or amine-containing materials, unsaturated hydrocarbons in plasticizers, and some solder flux residues. 

Polysulfide Propellant Cured with a Mono-functional Mercaptan , USP 3706610 (1972)... 

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). 

Aliphatic aldehydes, 13 571 physical properties of, 2 60t syntheses of, 12 187 Aliphatic a-hydroxy acids, 14 130 Aliphatic amine/polysulfide co-curing agent systems, 10 410... 

One-part clear acrylic latex sealant formulation, 22 42t One-part manganese dioxide-cured polysulfide formulation, 22 4 It One-part pigmented siliconized acrylic latex sealant, 22 42t One-part RTV silicones, 22 596 One-part silicone cross-linkers, 22 33t One-part silicone sealant formulation, 22 34t... 

The influence of ZnCFO concentration (3,0 5,0 7,0 phr) on formation of properties complex of the unfilled rubber mixes and their vulcanizates on the basis of isoprene rubber of the following recipe, phr isoprene rubber - 100,0 sulfur - 1,0 di - (2-benzothiazolyl) -disulfide - 0,6 N, N -diphenylguanidine - 3,0 stearic acid - 1,0, was carried out in comparison with the known activator - zinc oxide (5,0 phr). The analysis of Rheometer data of sulfur vulcanization process of elastomeric compositions at 155°C (fig. 5) shows, that on crosslink density and cure rate, about what the constants of speed in the main period (k2) testify, they surpass the control composition with 5,0 phr of zinc oxide. Improvement of the complex of elastic - strong parameters of rubbers with ZnCFO as at normal test conditions, and after thermal air aging (tab. 1), probably, is caused by influence of the new activator on vulcanization network character. So, the percent part of polysulfide bonds (C-Sx-C) and amount of sulfur atoms appropriating to one crosslink (S atoms/crosslink) in vulcanizates with ZnCFO are decreased, the percent part of disulfide bonds (C-S2-C) is increased (fig. 62). 

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