Influence of MCDA Isomerism on the Epoxy-MCDA Curing Reaction

Density functional thermodynamic studies were carried out for the epoxy-amine curing reaction with the example of the BASF product methylcyclohexyl diamine (MCDA, Baxxodur EC 210) to shed light on the effects of the reactivity of various MCDA isomers and subsequently on the resulting adducts’ performance. The reaction mechanisms of the cis versus trans and 2,4- versus 2,6-MCDA isomers were investigated and compared to experimentally available thermodynamic and kinetic data. The theoretical results show similar activation energies for all investigated isomers, indicating that the observed kinetic differences can be predominantly attributed to steric effects, an assumption also made in previous experimental and theoretical studies. The importance of hydrogen bonding was also emphasized for the first and second addition steps in the alcohol-catalyzed epoxy-amine curing reaction.