Polyamides and Amidoamines

TABLE 11.4 Curing Agent Selection for General-Purpose Room Temperature Curing Epoxy Adhesives 

Property Polyamine Amine adduct Polyamide Amidoamine 

The pot life of polyamide or amidoamine cured epoxy adhesives is generally on the order of hours at room temperature. Full cure is achieved in 5 to 7 days at room temperature, and handling strength is achieved in about 16 to 24 h. A faster cure can be achieved in 20 min to 4 h by heating to 60 to 150°C. When room temperature cures are required, an accelerator such as an amine is often added to the formulation. 

As a family of curing agents for epoxy resins, the amidoamines are lower in viscosity than the polyamides. They exhibit very good adhesive properties due to their chemical structure and easy penetration. Amidoamine cured epoxy adhesives have shown very good properties on concrete and other porous substrates. They cure extremely well under humid conditions. In fact amidoamine cured epoxy formulations have been used to cure underwater in certain applications. A typical general-purpose room temperature curing epoxy-amidoamine system is described in Table 11.7. This adhesive is used as a general-purpose metal-to-metal adhesive and body solder in the automotive industry. 

Aliphatic amines typically provide two-component, room temperature curing epoxy formulations with fast reactivity. They are often used as accelerators for polyamide and 

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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. 

When compared to other curing agents, polyamides and amidoamines offer the following three unique features. 

Both the polyamide and amidoamine curing agents can be accelerated by the addition of a tertiary amine such as DMP-10, tris(dimethylamino methyl) phenol. 

Chem. Descrip. Modified cycloaliphatic amine epoxy Uses Epoxy curing agent for high solids coatings accelerator for polyamide and amidoamine curing agents Features Good chem. resist, and low temp, cure (30-35 E) exc. blush resist. 

L6WiS BaS6S. Lewis bases contain an unshared pair of electrons in an outer orbital and seek reaction with areas of low electron density. They can function as nucleophilic catalytic curing agents for epoxy homopolymerization as cocuring agents for primary amines, polyamides, and amidoamines and as catalysts for anhydrides. Tertiary amines and imidazoles are the most commonly used nucleophilic catalysts. Several different mechanisms are possible ... 

Whereas most room temperature curing epoxy adhesives are cured with aliphatic amines, polyamides, or amidoamines, most elevated-temperature curing epoxy adhesives are cured with aromatic amines, modified aliphatic amines, alcoholic and phenolic hydroxyls, acid anhydrides, Lewis acids, and a host of other curatives. Latent curing agents, such as dicyan-diamide and imidazoles, are typically used in one-component epoxy adhesives systems. 

Uni-Rez . [Union Camp] Polyamide resin, amidoamine, rosin or rosin esters, maleic resin, or phenolic resin resins for inks and coatings. 

Other curatives, which react through addition mechanisms are phenolic resins, particularly if the hydroxyl/epoxy reaction is catalysed using a tertiary amine (usually accomplished at elevated temperatures), thiols, polysulphides and mercaptans (can be formulated to give very rapid cures), polyetheramines (relatively slow cures, which can be accelerated with nonyl phenol), polyamides (less reactive than their amine counterparts) and amidoamines (characterized as having very long pot lives). 

The condensation reaction ofTOFA with a polyalkylene polyamine such as diethyl-enetriamine (DETA), triethylenetetramine (TETA), or tetraethylenepentamine (TEPA) in a molar ratio 1 1 yields amidoamines ofTOFA (also called tall oil fatty acid polyamides). Typically the amidation reaction is conducted at temperatures between 250 and 290 and usually a mixture of tall oil fatty acid polyamide and the corresponding tall oil fatty acid imidazoline is obtained (Figure 3B.12). 

Amidoamines are derivatives of monobasic carboxylic acids (such as ricinoleic acid) and an aliphatic polyamine. Like the polyamides, amidoamines can be used over a range of additive levels to enhance a specific property. The reactivity of amidoamines with epoxies is similar to that of polyamides. However, amidoamines offer several advantages over aliphatic amines and poly amines more convenient mix ratios, increased flexibility, better moisture resistance than aliphatic poly amines, and lower viscosity and color than polyamides. 

Organic Acids and Their Derivatives (Anhydrides, Nitriles, Ureas). Alkyleneamines react with acids, esters, acid anhydrides or acyl hahdes to form amidoamines and polyamides. Various diamides of EDA are prepared from the appropriate methyl ester or acid at moderate temperatures (25,26). 

Amidoamine or polyamidoamine curing agents have reactivity with DGEBA epoxy resins that is similar to the polyamides. However, they are lower-viscosity products and are also lower in color. Amidoamines are derivatives of monobasic fatty carboxylic acids and aliphatic polyamines. Since the amidoamines have only one amide group per molecule, they are lower in molecular weight, viscosity, and amine functionality than the polyamides. 

As with amidoamine and polyamide cured adhesives, epoxy resins cured with aliphatic amines exhibit tensile shear strength that is dependent on the type of filler and concentration. Table 11.10 shows the effect of filler loading on strength of a simple general-purpose, room temperature curing epoxy adhesive composed of liquid DGEBA epoxy mixed with 10 pph of a tertiary amine. 

Polymerized fatty acid modification of resins and/or curing agents (e.g., polyamides, amidoamines)... 

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