Alternative monomers for 4,4′-methylenedianiline in thermosetting epoxy resins

4,4 '-Methylenedianiline (MDA) is utilized to produce high temperature epoxy resins as well as other high-performance composites; however, MDA is a known carcinogen and liver toxicant. Novel dianilines derived from both petroleum and biomass with different quantities and types of methyl and methoxy substituents on the aromatic ring were prepared and studied to reduce toxicity and carcinogenic aspects of the resulting material while maintaining thermal and mechanical integrity. These dianilines were primarily prepared by coupling commercial anilines using paraformaldehyde under acidic conditions. Another dianiline was prepared by nitration of bisphenol A and subsequent reduction of the nitrates to amines. Structure-toxicity relationships indicate that multiple substituents on the aromatic ring are necessary to reduce the toxicity of the dianiline. Epoxy-amine resins were prepared by blending the dianilines with 50 wt % Epikure W liquid amine curing agent and mixing with a stoichiometric amount of EPON 828 epoxy resin. Methoxy and methyl substituents increase the melting point of the dianilines by as much as 65 degrees C, thereby worsening the processing of these monomers as liquid thermoset resins. Structure-property relationships show that the addition of a methoxy group to the aromatic ring and moving the amine from the 4,4 ' position on the dianiline reduces the glass transition temperature (T-g) by approximately 10 degrees C. A single methyl group has little effect on T-g and two methyl groups increase the T-g only when both are ortho to the amine, yet this causes a large 14 degrees C increase in T-g. Thermal degradation profiles are not significantly affected by the dianiline. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48707.