Room Temperature Amine Curing Agents

Another method of decreasing amine odor and toxicity is to react a primary or secondary amine with an epoxy to yield a secondary or tertiary amine, respectively. In a patent of Texaco Development Corp., the toxicity and odor of aminopropyl derivatives of low molecular weight polyoxypropy-lenepolyamine curing agents were reduced by prereaction with aromatic epoxy compounds (Eq. 6). 

In some cases, prereaction can generate curing agents that are more reactive than the original amine. Alkylimine modification of polyoxyalky-lenepolyamines (Eq. 7) results in epoxy adhesives with gel times of 95 min 

A series of patents issued to Asahi Chemical Industry Co., deal with the modification of hexamethylenediamine by reaction with (meth)acrylic-, glycidyl ether-, hydroxyl-, amino-, amido-, or carboxy-substituted vinyl compounds, isocyanate, and amino acid compounds (Table IV). These modified amine curing agents are active at low temperatures and, in some cases, on wet substrates. Amine-substituted resole phenolics have also been described as useful epoxy curing agents. Preparation of these curing agents is via condensation of the phenol, formaldehyde, and polyamine (Eq. 8). 

One of the more useful benefits of the higher molecular weight amine curatives is their ability to act as tougheners, provided that the appropriate choice of backbone structure is made. Relatively low molecular weight 

One area where little moisture sensitivity can be tolerated is in field repair of structures such as ship hulls, pipelines, and concrete assemblies, where the bonding actually takes place in the presence of, or even under. 

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The two-part epoxy adhesive, readily available in hardware stores or other consumer outlets, comes in two tubes. One tube contains the epoxy resin, the other contains an amine hardener. Common diamine room temperature epoxy curing agents are materials such as the polyamides, available under the trade name Versamid. These polyamides are the reaction products of dimer acids and aUphatic diamines such as diethylenetriamine [111-40-0] ... 

Table 11.12 shows two rapid-setting, room temperature cure epoxy adhesives based on epoxy acrylate resins with aliphatic amine curing agents. These adhesives have gel times of less than 5 min for a 100-g mass. The bond strength development is rapid with handling strength occurring in about 1 h at room temperature. 

Other latent curing agents that are used in solid adhesives are dihydrazides and BF3-MEA complexes. These compositions are also stable at room temperature but cure when heated. Solid anhydrides can be used in one-component powder blends (e.g., 10 pph of trimellitic anhydride accelerated with 0.5 pph of 2-methylimidazole). Solid systems with aromatic diamines are prepared by comelting the solid epoxy with the amine. Typically 30 pph of curing agent is used.1... 

For maximum heat resistance, pyromellitic dianhydride is often used. The composition and properties of metal-to-metal adhesives based on a combination of epoxy novolac and a bisphenol A epoxy resin have been described in Sec. 12.5.1. Depending on the cure temperature and the choice of amine curing agent, strength as high as 3000 psi at room temperature and over 1000 psi in the range of-55 to + 150°C is possible. 

Aliphatic amine curing agents generate a high exotherm and have a short pot life, but can be cured at room temperature and do not require an intense post cure e.g. 

Amines generally do not need a catalyst, as the reaction with epoxy resins occurs spontaneously at room temperature. Therefore, amine curing agents can be used... 

In most cases the resins, curing agents, etc., used in adhesive foams are similar to those used in film adhesives. Expandable adhesive foams will obviously differ in that they will contain a blowing agent, while syntactic foams will contain hollow microballoons to reduce density. One-part heat cure pastes will contain liquid resins instead of solid resins. Two-part room temperature cure epoxy paste adhesives are generally cured with active amine curing agents, while one-part epoxy pastes, adhesive... 

The reaction was carried out at 100°C for about two hours until the theoretical isocyanate content, as determined by the di-n-butylamine titration method (27), was reached. The PU prepolymer with or without tertiary amine nitrogen groups was dissolved in dry MEK to obtain a prepolymer solution of 30-40% solids. It was then mixed with a mixture of 1,4-BD/TMP (4 1 by equiv. ratio) at an NCO/OH = 1.05/1.0 ratio in the presence of T-12 catalyst (0.05% based on total weight). The reaction mixture was cast in a metal mold treated with a release agent at ambient temperature. After standing 3-5 hours at room temperature, the mold was placed in an oven and post-cured at 100°C for 16 hours. The samples were then conditioned in a desiccator for one week before testing. 

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