Modification of aromatic diamine-cured epoxy resins by poly(oxymethylene) or hybrid modifiers containing poly(oxymethylene)

A copolymer comprising poly(oxymethylene) (POM, polyacetal) was used to improve the fracture toughness of a resin based on diglycidyl ether of bisphenol A (DGEBA) cured with 3,3′-dimethyl-5,5′-diethyl-4,4′-diaminodiphenyl methane. POM was a less effective modifier for epoxies and a third component was used as a toughener or a compatibilizer for POM. The third component includes polypropylene glycol-type urethane prepolymer (PU) and aromatic polyesters. The hybrid modifiers composed of POM and PU were more effective as modifiers for toughening epoxies than POM alone. In the ternary DGEBA/POM/PU (90/10/10wt ratio) blend, the fracture toughness, K_IC, for the modified resin increased 50% with retention of flexural properties and a slight decrease in glass transition temperature (T_g) compared with those of the unmodified epoxy resin. The aromatic polyesters include poly(ethylene phthalate) (PEP), the related copolyesters and poly(butylene phthalate). PEP was most effective of them as a third component in the hybrid modifier. In the ternary DGEBA/POM/PEP (85/15/10) blend, K_IC for the modified resin increased 70% with medium loss of flexural strength and retention of T_g. The toughening mechanism is discussed in terms of morphological and dynamic viscoelastic behaviour of the modified epoxy resin systems. ©1997 SCI