Aromatic polyamine hardeners

Aromatic polyamine hardeners These mostly solid hardeners include metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenyl siflfone. In general, these hardeners provide poorer bond strengths and are more sensitive to temperature cycling than the aliphatic amines. Shrinkage is also high... 

Because the reactants are not diluted in solventless coatings, pot-lives are short (0 5-2 hours). Because of short pot-lives, special twin-feed airless spray equipment is often used. Aromatic polyamines are preferred for curing, so that hardening times of 4-12 hours can be obtained even at 0-10° C. This better low temperature cure cannot be obtained in outdoor topcoats, where colour is important, since the aromatic polyamines discolour. 

Curing reactions of alicyclic polyamines with epoxy resins occur easily enough to allow carrying out at room temperatures. However, aromatic polyamines, acid anhydrides and phenol compounds usually need hardening accelerators, since their curing reactions require long times, even at elevated temperatures. Table 3 summarizes the general characteristics of these hardeners. 

The proposed dendro-aminosilane hardeners give the possibility to introduce the siloxane fragments into aromatic stmcture of diphenylolpropane based epoxy-amine network polymers. Additional hydrolysis of aminosilane oligomer creates the secondary nano-stmctured network polymer that improves the service properties of the compound. Branched (dendro) polyamine hardeners are novel direction in epoxy and cyclocarbonate and acryl resins chemistry. 

Other modifications of the polyamines include limited addition of alkylene oxide to yield the corresponding hydroxyalkyl derivatives (225) and cyanoethylation of DETA or TETA, usuaHy by reaction with acrylonitrile [107-13-1/, to give derivatives providing longer pot Hfe and better wetting of glass (226). Also included are ketimines, made by the reaction of EDA with acetone for example. These derivatives can also be hydrogenated, as in the case of the equimolar adducts of DETA and methyl isobutyl ketone [108-10-1] or methyl isoamyl ketone [110-12-3] (221 or used as is to provide moisture cure performance. Mannich bases prepared from a phenol, formaldehyde and a polyamine are also used, such as the hardener prepared from cresol, DETA, and formaldehyde (228). Other modifications of polyamines for use as epoxy hardeners include reaction with aldehydes (229), epoxidized fatty nitriles (230), aromatic monoisocyanates (231), or propylene sulfide [1072-43-1] (232). 

In addition to primary polyamines, secondary and tertiary amines are also utilized. The tertiary amines, such as methylated aliphatic aromatic amines,are most commonly utilized. They can best be described as catalysts, rather than hardeners, since they speed up a reaction and contribute to cross-linking, rather than entering into the reaction itself. 

Aromatic amines are solids at room temperature and are routinely melted at elevated temperatures and blended with warmed resin. Eutectic mixtures of metaphenylene and methylene dianiline exhibit a depressed melting point, producing an aromatic hardener that remains liquid over short periods of time. Pot life is considerably longer that that of aliphatic polyamines. Cure at elevated temperature is needed to develop optimum properties, which are maintained at up to 15()°C. Aromatic amines have better chemical and thermal resistance than aliphatic polyamines. 

A two-component epoxy system consists of a resin and a hardener, along with possible additives such as accelerators, reactive diluents, resin modifiers, plasticizers, and fillers. Typical hardeners include aliphatic polyamines, which cure at room temperature or at slightly elevated temperatures polyamides, which provide flexibility and are widely used aromatics, which are solid and anhydrides, which require elevated temperature cure and produce thermally stable but brittle adhesives. Low molecular weight epoxies are liquid and are usually cured by amines, carboxylic acid anhydrides, and Lewis acid and base catalyst. Higher molecular weight epoxies are cured through their hydroxyl groups. Cure of epoxies involves an exothermic reaction. 

---