Characterisation and cure kinetics of multi-aromatic tetra-functional epoxy resins

A systemic study of the impact of aromatic substitution on the reaction rate and network performance of isomers of tri-phenyl epoxy resins cured with two different anhydride hardeners is presented here. The epoxy resins are based upon the structure N, N, N, N-tetraglycidyl bis (aminophenoxy) benzene (TGAPB) with substitution varying from all meta (133 TGAPB), to meta and para (134 TGAPB), and finally to an all para substituted (144 TGAPB) structure. The hardeners used to cure resins were methyl nadic anhydride (MNA) and methyl hexahydropththalic anhydride (MTHPA) catalysed with imidazole. Increasing para substitution increased reaction rate, promoted the onset of vitrification and increased epoxide conversion. Thermal properties such as Tg and CTE both increased consistently with increasing para substitution, although thermal stability as measured via thermogravimetric analysis decreased. The flexural strength increased, modulus decreased while ductility almost doubled after post-cure as measured by the work of fracture and displacement at failure. Increased rigidity of a tri-aromatic all para substituted epoxy resin, was demonstrated to be extremely beneficial towards improved ductility, while either improving or maintaining important physical, thermal and mechanical properties apart from thermal stability