Epoxy aliphatic amines

In the well-recognized epoxy-aliphatic amine reaction, the primary or secondary amine adds to the epoxy ring, forming a tertiary amine, as shown in Fig. 5.2 (top). The formed hydroxyl groups accelerate the amine curing, and with excess epoxy present, the secondary hydroxyl groups can also add to the epoxy ring, as shown in Fig. 5.2 (bottom). 

Many of the copolymer-forming reactions employed to compatibilize PA blends with a second immiscible polymer have been studied by Orr et al. (2001) who determined that the order of increasing reactivity in functionalized polymer pairs is acid/amine, hydroxyl/(anhydride or acid), aromatic amine/epoxy, aliphatic amine/ epoxy, acid/oxazoline, acid/epoxy, aromatic amine/anhydride, and aliphatic amine/ anhydride (most reactive). 

A = bisphenol A epoxy—aliphatic amine hardener 1 -B = bisphenol A epoxy—aromatic amine hardener 1 -C = bisphenol F epoxy (epoxy novolac) 2-D = polyester resin—chlorendic acid type 2- E = polyester resin—bisphenol A fumarate type 3- F = vinyl ester resin 3-G = vinyl ester novolac resin ... 

Melt reaction mechanisms of tertiary aliphatic amine catalyzed phenolic-epoxy reactions were proposed to begin with a trialkylamine abstracting a phenolic hydroxyl proton to form an ion pair (Fig. 7.36). The ion pair was suggested to complex with an epoxy ring, which then dissociated to form a /1-hydroxycther and a regenerated trialkylamine.87... 

Polystyrene insulation on magnet wire 0.29 Encapsulated with B-staged aromatic amine cured aliphatic amine cured bisphenol A-epichlorohydrin epoxide (epoxy transfer moulded). Impregnate. 

The best performing coatings were the vinyl ester, the bisphenol A epoxy cured with an aliphatic amine, and a novolac epoxy cured with a mixed aromatic/cycl oal i phati c amine. The saturated polyester, and a bisphenol A epoxy cured with a polyamide amine showed significant deterioration of the coating material in the acid, and corrosion of the underlying steel. Two types of novolac epoxies cured with aromatic amines showed intermediate performance. 

Curing agents account for much of the potential hazard associated with use of epoxy resins. There are several major types of curing agents aliphatic amines, aromatic amines, cycloaliphatic amines, acid anhydrides, polyamides, and catalytic curing agents. The latter two types are true catalysts, in that they do not participate in the curing process. 

Asa rule of thumb, epoxies cured with aliphatic amines, cause a majority of explosives and propellants to be excessively reactive. Epoxies cured... 

A tertiary amino group formed in curing with aliphatic amines can sometimes catalyze the epoxy group polymerization. When aromatic amines are used as curing agents, such reactions do not take place at all. 

The hisphenol A-derived epoxy resins are most frequently cured with anhydrides-, aliphatic amines, or polyamides. 

The bisphenol A-derived epoxy resins are most frequently cured with anhydrides, aliphatic amines, or polyamides, depending on desired end properties. Some of the outstanding properties are superior electrical properties, chemical resistance, heat resistance, and adhesion. Conventional epoxy resins range from low viscosity liquids to solid resins. 

In addition to electrical uses, epoxy casting resins are utilized in the manufacture of tools, ie, contact and match molds, stretch blocks, vacuum-forming tools, and foundry patterns, as well as bench tops and kitchen sinks. Systems consist of a gel-coat formulation designed to form a thin coating over the pattern which provides a perfect reproduction of the pattern detail. This is backed by a heavily filled epoxy system which also incorporates fiber reinforcements to give the tool its strength. For moderate temperature service, a liquid bisphenol A epoxy resin with an aliphatic amine is used. For higher temperature service, a modified system based on an epoxy phenol novolak and an aromatic diamine hardener may be used. 

In the case of epoxy networks with a secondary diamine, like DMHMDA, the network architecture is such that flexible aliphatic sequences are present as chain extenders between the crosslink points. In such architectures, the motions of the HPE units can develop towards other HPE sequences (either along the chain or spatially neighbouring) without involving the crosslink points in their cooperativity. Thus, with these systems a different nature of cooperativity exists compared to the other network architectures. The introduction of an antiplasticiser in such a local packing does not affect the cooperativity as much as with the densely crosslinked architecture, for the crosslinks are not so much involved. Once more, it is important to point out that the flexible nature of the aliphatic amines does not matter since the same behaviours are observed for fully aromatic systems with identical architecture [68]. 

The mechanisms of radiation damage and effects of hardeners were studied recently by pulse radiolysis [89], The epoxy resins require a relatively large amount of curing agents (hardeners), most of them are aromatic and aliphatic amines such as diamino diphenyl methane or triethylene tetramine. On the basis of the emission spectra and kinetic behavior of excited states observed, the radiation resistance of aromatic and aliphatic amine curing epoxy resin was explained by internal radiation protection effects due to energy transfer. 

Primary and secondary aliphatic amines react relatively rapidly with epoxy groups at room or lower temperature to form three-dimensional crosslinked structures. The resulting cured epoxies have relatively high moisture resistance and good chemical resistance, particularly to solvents. They also have moderate heat resistance with a heat distortion temperature in the range of 70 to 110°C. Thus, short-term exposures of cured adhesive joints at temperatures up to 100°C can generally be tolerated. 

These aliphatic amines can also be cured at elevated temperatures to provide a more densely crosslinked structure with better mechanical properties, elevated-temperature performance, and chemical resistance. Table 5.3 illustrates the effect of curing temperature on the bond strength of DGEB A epoxy with two different aliphatic amines. 

Other amines, such as aromatic or cycloaliphatic, are less reactive and generally require elevated-temperature cures that result in higher heat distortion temperatures (140 to 150°C). However, aromatic amine adducts of liquid epoxies can be accelerated to cure at room temperature. Aliphatic amines can also be accelerated. 

Epoxy resin formulations containing aliphatic amines will blush and provide an oily surface under very humid conditions. This is due to a reaction of the amine primary hydrogen atoms with carbon dioxide. Resistance to blushing is more important for coatings than for... 

In adhesive formulations, aliphatic amines are most commonly used to cure the DGEBA type of epoxy resin. Aliphatic amines are not widely used with the non-glycidyl ether resins, since the amine-epoxy reaction is slow at low temperatures. The reaction usually requires heat and accelerators for an acceptable rate of cure. Aliphatic amines are primarily used with lower-viscosity DGEBA resins because of the difficulty in mixing such low-viscosity curing agents with the more viscous epoxy resins. 

There are several reasons why unmodified aliphatic amines, such as those described above, are less widely used than other curing agents in epoxy adhesive systems. These include... 

Glycidyl Adducts of Aliphatic Amines. An aliphatic amine such as diethylenetriamine can be partially reacted with an epoxy, such as a DGEBA resin, to produce a low-volatility adduct. In a typical reaction, the epoxy is added slowly to a large excess of DETA. The reaction is maintained at 75°C by cooling. The reaction products are continuously agitated effectively to provide for good contact and uniform concentration effects. At the end of the reaction, excess DETA is vacuum-distilled away from the adduct. 

Two curing agents that have found their way into many epoxy adhesive formulations are the polyamides and amidoamines. These are commonly used in the hardware store variety two-part epoxy resins that cure at room temperature. Both are reaction products of aliphatic amines, such as diethylenetriamine, and should be included under the subclassification of modified amines. However, these products have such widespread and popular use, they are addressed here as a separate classification. 

Polyamide cured DGEBA epoxies provide improved flexibility, moisture resistance, and adhesion over aliphatic amines alone. However, polyamide cured epoxies are generally inferior in thermal resistance and shear strength due to the reduction in crosslink density. Polyamide cured epoxies lose structural strength rapidly with increasing temperatures and... 

The mix ratio of anhydride to epoxy resin is less critical than with amines and can vary from 0.5 to 0.9 equivalent of epoxy. The specific ratio is generally determined experimentally to achieve desired properties. Compared to aliphatic amine cures, the exotherm generated by anhydride cured epoxies is low. Elevated-temperature cures up to 200°C and postcures are required to develop optimal properties. 

The epoxy product cured with BF3-MEA is densely crosslinked and has excellent physical properties at high temperatures (150 to 175°C). When reacted with an unmodified epoxy resin, the resulting product is very hard and brittle. The chemical resistance, however, is only fair and somewhat less than that of epoxies that are cured with aliphatic amines. 

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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