Thermal and mechanical properties of aminopropoxylate-cured epoxy matrices

Bisphenol A diglycidyl ether–aminopropoxylate mixtures have been characterized with respect to their viscosities in the presence and absence of butanediol diglycidyl ether (reactive diluent), and their curing patterns have been studied at room temperature with or without 2,4,6‐tris(dimethylaminomethyl)phenol (initiator/accelerator). A priori, these mixtures are expected to provide low connectivities to infinite networks at gelation, a prediction supported by the multiple glass‐transition‐temperature (Tg) behaviour of their cured forms. The effect of the aminopropoxylate curing agent chemistry/functionality, and the presence or absence of accelerator and reactive diluent on the tensile and impact behaviour of cured materials, is reported. An expectation of increased importance of polymerization with increases in the initiator/accelerator levels, alongside epoxy–amine addition reactions, has not been evidenced by the mechanical measurements. For diglycidyl ether bisphenol A–aminopropoxylate epoxy systems, in the glycidyl ether/reactive hydrogen molar ratio range 0·80 (set A) to 1·95 (set B), the tensile failure mode is brittle fracture. For the set A formulations, this mode of failure persists up to reactive diluent loadings of 1·01wt% based on the weight of bisphenol A diglycidyl ether. Beyond 1·01wt% reactive diluent loadings, the set A formulations show ductile failure with yielding; the tensile toughness increases with increases in reactive diluent levels. For the set B formulations, and for all reported loading levels of reactive diluent, the castings failed in brittle fashion with pronounced cavitation and stress whitening. © 1998 Society of Chemical Industry