Cure of epoxy resins with esters of cyanoacetic acid

Abstract

Esters of cyanoacetic acid are a novel class of epoxy curing agents. The model reaction between ethyl cyanoacetate (ECA) and phenyl glycidylether (PGE) yielded a cyano‐spiro‐dilactone under conditions similar to the resin cure. The structure of the spiro compound resulting from 2 ECA and 2 PGE was elucidated by MS, IR, 1H‐, and 13C‐NMR techniques. Ammonia is split off from 1 ECA and acts in statu nascendi as a satellite hardener. An overall model reaction equation for the cyanoacetyl cure is proposed. The cure of bisphenol A–diglycidylether (BADGE) with ECA and with neopentylglycol‐biscyanoacetate (NPGCA) is described over a wide range of the molar ratio. Clear and tough solids are obtained with a glass transition temperature up to 130°C. Cyanoacetates are latent hardeners requiring a curing initiator. Since N‐4‐chlorophenyl N′‐dimethylurea is a latent initiator, liquid “one‐shot” systems can be formulated that are stable at room temperature and harden quickly above 120°C. Heat aging properties of cured specimens are reported. A series of novel liquid, resinous, and crystalline cyanoacetates and their potential as curing agents are described.