Diamine curative

Diamine curatives were the first cross-linking agents for fluorocarbon mbbers. They are corrosive to mild steel molds and have been replaced in many appHcations by the bisphenol or other more recent cure systems. Nevertheless, some diamines are stiU used for food-contact appHcations of fluorocarbon mbbers and in zinc-free cures of halobutyl mbbers for pharmaceutical stoppers. Methylene dianiline and triethylene tetramine are cross-linking agents for ethylene—acryflc elastomers. 

If a diamine curative is used, the amine groups (NH2) will react with an isocyanate group of the prepolymer to form a urea bond. The remaining amine group will react with a further isocyanate group to extend the chain, as shown in Figure 2.30. 

When a diamine curative is used, urea bonds are formed. These bonds also play an important part in the hydrogen bonding process. The unbonded urea has an absorption band at approximately 1690 cm1 and the bonded urea at 1682 cm-1. The time sequence spectra (Figure 2.37) show the formation of the bonded urea bands over the first hours of curing. 

When the prepolymer chain is extended with a diol, the polymer formed has only urethane linkages. The polymer formed with the diamine chain extender is strictly a polyurethane polyurea. The first urethane component is from the initial chain extension when the prepolymer is prepared. A diamine curative will form urea linkages (Figure 2.3) between chains. 

Polaroid Corporation, Recent Developments in the Use of Polacurd No. 740M Diamine Curative, October, 1978. 

Polaroid Corporation, Trimethylene Glycol Di-p-Aminobenzoate - A Development Diamine Curative for Cast Elastomers,... 

The standard diol chain extender used for the synthesis of PU elastomers was 1,4-butane diol (BDO). Products from this type of material, as a generalization, have inferior properties to aromatic diamine curatives and various alternatives have been introduced over the last few years to attempt to simulate the properties of the urethane diamine cure or to produce special effects. Examples of these are shown below ... 

Versalink, Diamine curative oUgomeric diamine curatives, Air Products and Chemicals, Inc. 

Since the copolymer has a saturated backbone, it must be peroxide cured. However, a third momomer is added for the terpolymer version of AEM. This terpolymer with the active site can be cured with a diamine curative to achieve significantly better compression set resistance. This third monomer provides a carboxyl group that can react with the diamine curative, to give crosslinks. 

However, diamine curatives can also be used as chain extenders to cure the isocyanate-terminated prepoiymer as well. 

TDI-terminated prepolymers can impart unique properties to a PUR application, especially if a diamine curative is being used. MDI-terminated prepolymers have difficulty matching certain physical properties. 

The LOI behavior of phosphorus-containing siliconized epoxy followed the same trend as that of siliconized epoxy system. Epoxy and siliconized epoxy materials cured with the phosphorus diamine curative exhibited the maximum LOI value of 42, which maybe due to the consequence of the char enrichment of phosphorus and the char protecting effect of silicone to exhibit the synergistic effect of both silicone and phosphorus on LOI enhancement [50-54]. Thus simultaneously incorporating silicone and phosphorus into epoxy resin would render these epoxies as flame-retardant polymers and can be rated as the best flame retardant material. 

The polyamide copolymer of dodecanoic acid with methylenedi(cyclohexylamine) (MDCHA, PACM) was sold as continuous filament yam fiber under the tradename QIANA. As late as 1981, over 145,000 t was produced using high percentages, typically 80%, of trans, trans MDCHA isomer. The low melting raffinate coproduct left after t,t isomer separation by fractional crystallisation was phosgenated to produce a Hquid aUphatic diisocyanate marketed by Du Pont as Hylene W. Upon terrnination of their QIANA commitment, Du Pont sold the urethane intermediate product rights to Mobay, who now markets the 20% trans, trans—50% cis, trans—30% cis, cis diisocyanate isomer mixture as Desmodur W. In addition to its use in polyamides and as an isocyanate precursor, methylenedi (cyclohexyl amine) is used directiy as an epoxy curative. The Hquid diamine mixture identified historically as PACM-20 is marketed as AMICURE PACM by Anchor Chemical for performance epoxies. 

Cyclohexanediamine is marketed by Milliken Chemical as an epoxy curative, Millamine 5260. It may be adducted with epichlorohydrin to generate solventiess low viscosity curatives for varnishes and surface coatings (76). Other cycloaHphatic diamines have long been modified as epoxy curatives to modify their reactivity profile (77). 

MCHD from ring reduction of I DA (60,78) has been cited as an epoxy curative (79) and is available from Air Products and Chemicals as a developmental cycloaHphatic diamine. Ring reduction of stericaHy hindered arylenediamines such as diethyltoluenediamine [68479-98-1J -ptovides slower-reacting alkylated 1,3-cyclohexanediamines for polyurethane, polyurea, and epoxy use (80). 

Amine Cross-Linking. Two commercially important, high performance elastomers which are not normally sulfur-cured are the fluoroelastomers (FKM) and the polyacrylates (ACM). Polyacrylates typically contain a small percent of a reactive monomer designed to react with amine curatives such as hexamethylene-diamine carbamate (Diak 1). Because the type and level of reactive monomer varies with ACM type, it is important to match the curative type to the particular ACM ia questioa. Sulfur and sulfur-beating materials can be used as cure retarders they also serve as age resistors (22). Fluoroelastomer cure systems typically utilize amines as the primary cross-linking agent and metal oxides as acid acceptors. 

The chemistry of this cure system has been the subject of several studies (44—47). It is now generally accepted that the cure mechanism involves dehydrofluorination adjacent to hexafluoropropylene monomer units. The subsequent fluoroolefin is highly reactive toward nucleophilic attack by a variety of curatives (eg, diamines, diphenols). 

The major problem is moisture that is absorbed into the polyurethane system or into the curative and auxiliary materials. Free water will liberate carbon dioxide when the chain extension is carried out. It is important to keep the reactants dry, as any moisture that may have come in contact with the prepolymer will react to give an amine and carbon dioxide. This amine reacts with more isocyanates to form a disubstituted diamine. The reaction is outlined in Figure 2.9. 

The simple linear aliphatic diamines, H2N(CH2)n NH2, can be used as curatives in adhesives. For small values of n, the short distance between the amine groups can hinder the reaction of the second amine and slow the... 

Curalon [Uniroyal]. TM for a series of urethane curatives. Curalon L, a mixture of hindered aromatic primary diamines. Curalon M, p,p methylene-bis(o-chloroaniline). 

Solventless, elastomeric coatings were reported by Bonk et al. (169). The sprayable compositions were based mainly on diethylene glycol adipates, Isonate 143-L, and various diamine chain extenders and curatives. Airless Binks spray guns were employed in the... 

It is prepared by the reaction of sodium or potassium thiocyanate with chloroformic acid methyl ester, and the intermediate product reacts with o-phenylene diamine to form the thiophanate. Thiophanate-methyl is a colourless, crystalline compound hardly soluble in water. It forms unstable salts and complexes with bivalent ions in alkaline solutions. The range of action of each thioallophanic acid derivative is identical with that of the benzimidazole derivative into which it is converted in the plant. Thiophanate-methyl has both a preventive and a curative action. 

Hexcekure. [2 1and] Amines or diamines epoxy curatives. 

CCRIS 6680 Cyclohexanemethanamine, 5-amino-1,3,3-trimethyl- EINECS 220-666-8 HSDB 4058 Isophorone diamine UN2289 Vestamin TMD. Epoxy curative for flexible coatings, adhesives, castings and composites. Degussa-Hiils Corp. 

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