Study of cross-linking reactions of melamine/formaldehyde resin with hydroxyl functional polyester by generalized 2-D infrared spectroscopy

To better understand the reaction pathways, the reactions of a highly subst ituted methylated melamine/formaldehyde resin with a hydroxyl functional po lyester resin were followed by obtaining a series of transmission FTIR spec tra during reaction at 120 degrees C, The resulting spectra represent the s pectra of the reaction mixture as a function of reaction time. A generalize d 2-D correlation treatment to this data set gives the synchronous and asyn chronous correlation matrices. From these matrices, the reaction pathways c an be deduced. Analyzing the initial and late stages of the reaction separa tely clearly shows the reaction pathways change after all the hydroxyl grou ps on the polyester have reacted. The early stage of the cure process, prio r to consumption of all the polyester hydroxyl groups, is marked by transet herification reactions, leading to the formation of ether cross-links. Reac tions to form self-condensed methylene bridge structures between two melami ne molecules may proceed through an ether intermediate. After all the polye ster hydroxyl groups have been consumed, the reaction pathways change. The concentration of methoxymethyl groups on the melamine continued to decrease , albeit at a slower rate. (C) 2000 Elsevier Science B.V. All rights reserv ed.