Hardening Composition of Epoxy Resins

One interesting hardening composition is an aniline formaldehyde resin, also in solution in triaryl phophite. Here it is appropriate to mention the growing of phosphorus compound in the curing of epoxy resins; recently a number of organic phosphates have been describe as curing assistants, for any type of polyepoxide and almost any type of hardener, including anhydride, polyamine, polyamide and polysulphide. Although a curing assistant may accelerate the rate of curing, it is also said to improve the ratio of usable life to curing time, in other words to increase the efficiency of the hardener system.

Styrene maleic anhydride copolymers of high molecular weigh are wellknown plastic; recently, related low molecular weight substances in the form of linier polyanhydrides (or partial esters thereof) have been recommended as curing agents, and these are soluble in heated resin.

Quaternary ammonium salts made by neutralizing quaternary ammonium hydroxide with organic acids have been suggested as hardener, and it is important to note, for both glycidyl epoxies.

Certain tertiary amines which can be prepared by the Mannich reaction, in particular tris phenol, are used in some adhesive applications. Their behaviour is catalytic, they initiate polymerization of epoxide groups and also accelerate curing with crosslinking curing agents. A similar reaction product from phenol, an aliphatic amine and also formaldehyde, has superior properties.