m-Xylylenediamine
m-Xylylenediamine combines an aromatic ring with aliphatic amine groups, giving epoxy coatings a fast, low-temperature cure and strong chemical resistance.
MXDA is a benzene ring with two aminomethyl (–CH₂NH₂) groups in the meta positions (molecular weight 136.19 g/mol). Each primary amine carries two reactive hydrogens, so the amine hydrogen equivalent weight (AHEW) is about 34. It is a colorless liquid that boils at about 247 °C and freezes at about 14 °C.
MXDA and its adducts cure epoxy resins in tank and pipe linings, chemical-resistant floors, marine and protective coatings, and adhesives. It is chosen for fast cure at ambient and low temperatures, good gloss and solvent and acid resistance. It is often supplied as a modified hardener, such as an epoxy adduct or Mannich base, to reduce blush and volatility.
MXDA is described as araliphatic: its amine groups sit on CH₂ carbons rather than directly on the ring, so they react like aliphatic amines, while the aromatic ring adds rigidity to the cured network.
MXDA is corrosive to skin and eyes, harmful if swallowed or inhaled, and a skin sensitizer. Wear chemical-resistant gloves, eye and face protection and ensure good ventilation. Store under nitrogen in tightly closed containers to prevent carbamate crust formation from air, and keep above its freezing point.
The amine groups are attached to aliphatic CH₂ carbons that are themselves attached to an aromatic ring. The amines behave like fast aliphatic amines, while the ring stiffens the cured network.
Use equivalents: phr = AHEW × 100 ÷ EEW. With an AHEW of about 34 and a resin EEW of 190, that is roughly 18 parts per hundred resin. Formulated hardeners have their own mix ratios on the TDS.
Free primary amines react with carbon dioxide and moisture at the surface to form carbamates, especially in cold, humid conditions. Adducted hardeners, induction time and good ambient conditions reduce blush.
