Synthesis of a soluble azomethine-containing bisphenol and the properties of its modified epoxy thermosets

A soluble bisphenol containing azomethine moiety and aromatic ether linkage, 2,2'-bis {4-[4-(hydroxy) phenytiminomethylidene] phenoxyphenyl} propane (BHPP), was synthesized from the reaction of 4-hydroxybenzaldehyde with 2,2'-bis (4-aminophenoxy phenyl) propane (BAPP) and characterized by IR, H-1 NMR, C-13 NMR, and elemental analysis. To improve the overall properties of epoxy/diamine thermoset, ternary-curing systems combined BAPP/BHPP with diglycidyl ether of biphenyl A (DGEBA) were designed. It was found that the curing behavior and properties of the BAPP/DGEBA system changed dramatically due to the introduction of BHPP. The hybrid-curing agents BAPP/BHPP exhibited more reactivity toward oxirane group than did BAPP. All the epoxy thermosets had high thermal properties, e.g., glass transition temperatures (T(g)s) are between 145 and 170 degrees C, 5% weight loss temperatures over 329 degrees C, integral procedure decomposition temperature (IPDT) varied with 682-1085 degrees C and good flame retardancy for their high limited oxygen index (LOI) values beyond 28.4