Density Functional Investigation of Melamine−Formaldehyde Cross-Linking Agents. 1. Partially Substituted Melamine

Computational modeling has been performed on the cross-linking mechanism of partially substituted melamine reacting with poly(vinyl alcohol). Ab initio calculations were performed with density functional theory employing the BLYP functional and double numerical DND basis set. The mechanism, general acid catalysis, has been modeled with respect to structures, protonation, and reaction with a polymer. Protonation of the oxygen is required initially, followed by liberation of methanol. The reaction can take one of two pathways after methanol liberation. The conjugate base of the weak acid can abstract a proton, generating a Schiff-base intermediate. The O−H on the polymer then adds to the C−N double bond, producing the polymer−melamine bond. The alternative is that the polymer adds to the charged melamine, using the specific acid catalysis mechanism. After polymer addition, the proton is abstracted, producing the product.