Thermal and mechanical properties of aminopropoxylate-cured epoxy matrices

Bisphenol A diglycidyl ether-aminopropoxylate mixtures have been characteri zed with respect to their viscosities in the presence and absence of butane diol diglycidyl ether (reactive diluent), and their curing patterns have be en studied at room temperature with or without 2,4,6-tris(dimethylaminometh yl) phenol (initiator/accelerator). A priori, these mixtures are expected to provide low connectivities to infi nite networks at gelation, a prediction supported by the multiple glass-tra nsition-temperature (T-g) behaviour of their cured forms. The effect of the aminopropoxylate curing agent chemistry/functionality, an d the presence or absence of accelerator and reactive diluent on the tensil e and impact behaviour of cured materials, is reported. An expectation of i ncreased importance of polymerization with increases in the initiator/accel erator levels, alongside epoxy-amine addition reactions, has not been evide nced by the mechanical measurements. For diglycidyl ether bisphenol A-aminopropoxylate epoxy systems, in the gly cidyl 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 1.01 wt% based on the weight of bisphenol A diglycidyl ether. Beyond 1.01 wt% react ive diluent loadings, the set A formulations show ductile failure with yiel ding; the tensile toughness increases with increases in reactive diluent le vels. For the set B formulations, and for all reported loading levels of re active diluent, the castings failed in brittle fashion with pronounced cavi tation and stress whitening. (C) 1998 Society of Chemical Industry.