Curing behavior and thermal properties of TGDDM copolymerized with a new pyridine-containing diamine and with DDM or DDS

A new pyridine-containing diamine, 4,4'-(pyridine-2,6-diylbis(oxy)) dianiline (PDD) was used as curing agent for a tetra-epoxy resin, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM). The chemical reactivity of the diamine was evaluated using Friedman's method, and compared with traditional diamine curing agents, 4,4'-diaminodiphenylmethane (DDM) and diaminodiphenylsulphone (DDS). PDD was found to be more reactive with the epoxy groups of TGDDM than DDS but less reactive than DDM. The dynamic mechanical thermal analysis showed all materials had 'Tgs' above 250 °C and thermosets formed from TGDDM with blends of PDD with either DDM or DDS had 'Tgs' which increased linearly with composition. Thermogravimetric analysis (TGA) of TGDDM/PDD under argon atmosphere gave a distinctive two-stage decomposition curve compared with the approximately single step observed when TGDDM was cured by the traditional amines. When carried out under air atmosphere, the TGA mass loss occurred in multiple stages and the rate of degradation for the PDD-cured TGDDM was slower than that for DDM- and DDS-cured epoxy resin. This suggests PDD enhances the flame retardancy of the cured thermosets when compared to the more traditional diamine curing systems.