APTES

What it is

APTES is an organosilane with three ethoxy groups on silicon and a primary amine at the end of a propyl chain (molecular weight 221.37 g/mol). It is a clear, colorless liquid with an amine odor that boils at about 217 °C.

Role in coatings

• Adhesion promoter: added in small amounts to epoxy, polyurethane, acrylic and phenolic coatings, sealants and adhesives, or applied as a dilute primer on glass, metal, concrete and mineral substrates.
• Filler treatment: used to surface-treat glass fibers, silica and other fillers so they bond to the resin, and to functionalize nanomaterials such as graphene oxide.

Chemistry & key properties

The silane works in two steps:

• Inorganic side: the ethoxy groups hydrolyze with water to silanols (releasing ethanol), which condense with hydroxyl groups on the substrate and with each other to form Si–O–substrate and Si–O–Si bonds.
• Organic side: the primary amine reacts with epoxide groups, reacts very rapidly with isocyanates to form ureas, or interacts with other resins.
• Selection: amino silanes suit epoxies and many urethanes; epoxy-functional silanes are often chosen when amine reactivity is a problem.

Handling & storage

APTES is corrosive to skin and eyes, a skin sensitizer and harmful if swallowed, and it releases ethanol when it hydrolyzes. Wear chemical-resistant gloves and eye protection and use ventilation. Store tightly sealed and dry, because moisture causes premature hydrolysis and condensation.