Polysulfides liquid

The dry peroxide, added to cause cross-linking in liquid polysulfide polymers with pendant thiol groups, caused sparking or ignition, depending on the scale of the... 

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 ... 

Epoxy-Liquid Polysulfide Blends Epoxy resins in combination with liquid PSs appear to possess many added advantages as the elastomeric PS segments in epoxy chains impart permanent flexibility [18]. Epoxy-liquid PS blends have been reported as binders for Army illuminating formulations [8]. Similarly, novolac epoxy-liquid PS blends have been reported for inhibition of composite propellants [19]. 

The most significant improvement came in the early 1940s when a method for preparing thiol-terminated liquid polysulfides was developed. Cure of the liquid polysulfides could be accomplished by oxidative coupling. Thus, in effect, a mbber could be compounded without the need of heavy mixing equipment. One of the first large-scale applications of the liquid polysulfides was as a binder for solid rocket fuel. From about 1946 until 1958, these binders were used in various rocket systems and the aliphatic polysulfides achieved commercial success. The switch to predominately liquid-fueled rockets in 1958 ended this phase of the polysulfide business. 

Since then, uses have shifted more toward civilian applications. Polysulfides have unusually good resistance to solvents and to the environment and good low temperature properties. This makes them particularly useful in a variety of sealant applications. For example, the outstanding resistance of polysulfides to petroleum (qv) products has made them the standard sealant for virtually all aircraft integral fuel tanks and bodies. Another important application is in insulating glass window sealants (qv). Sealants based on liquid polysulfides have had an excellent record since the 1950s and are the worldwide market leader in this application. 

Diisocyanates or Polyisocyanates. The thiol end groups of the liquid polysulfides are quite reactive with isocyanates (eq. 3). Typical diisocyanates, such as 1,3-toluene diisocyanate (m-TDI) and diphenylmethane-4,4,-diisocyanate (MDI), are effective in curing liquid polysulfides. Using liquid polysulfides in-... 

Formulation. Polysulfide-based sealants are formulated with appropriate ingredients to obtain the desired properties for a particular application. A typical formulation contains liquid polysulfide polymer, curing agent, cure accelerators (bases) or retarders (acids), fillers, plasticizers, thixotropes, and adhesion promoters. 

Worldwide production capacity of liquid polysulfides is about 33,000 t with manufacturing sites in the United States, Japan, and Germany. Total consumption is about 28,600 t. Approximately 50% is for insulating glass sealants, 30% for construction applications, and 10% for aircraft sealants. In addition, 909 t of the solid polysulfide rubbers are sold each year. 

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)... 

The tertiary amines and TETA are used at about 10 pph, and the liquid polysulfide is used at about 50 to 100 pph. 

For adhesive systems, the liquid epoxy resins most widely used with LP-3 polymers are liquid unmodified and diluent-modified bisphenol A resins and liquid blends of bisphenol A and bisphenol F resins. Solid bisphenol A, multifunctional, and aliphatic diepoxy resins have also been used. Ratios of liquid polysulfide polymer to epoxy are in the range of 1 2 to 2 1. The effect of various degrees of polysulfide on cure properties of a DGEB A epoxy is shown in Table 7.7. An increase in elongation and impact strength is the result of increased amounts of the liquid polysulfide polymer. 

Suitable curatives for the polysulfide-epoxy reaction include liquid aliphatic amines, liquid aliphatic amine adducts, solid amine adducts, liquid cycloaliphatic amines, liquid amide-amines, liquid aromatic amines, polyamides, and tertiary amines. Primary and secondary amines are preferred for thermal stability and low-temperature performance. Not all amines are completely compatible with polysulfide resins. The incompatible amines may require a three-part adhesive system. The liquid polysulfides are generally added to the liquid epoxy resin component because of possible compatibility problems. Optimum elevated-temperature performance is obtained with either an elevated-temperature cure or a postcure. 

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