Real Time NMR analysis of Melamine Formaldehyde Resin Reactions

This investigation was carried out on behalf of the Momentive Specialty Chemicals Pty Ltd, Mt Maunganui. The aim of the investigation was to develop a method to analyse the formation of melamine formaldehyde resins via an in situ real time NMR experiment leading to quantitative NMR intensities of the resin up to the stages of its Industrial Resin Endpoint (IRE). \nIn order to run an in situ reaction for the melamine formaldehyde resin system and monitor it in real time, both qualitative and quantitative NMR acquisition methods were required. The qualitative method was power gated and used to obtain results in situ and in real time. However to render it quantitative, it was necessary to develop a quantitative method which was initially executed to obtain a conversion factor for relating the qualitative results obtained in the in situ experiment to quantitative results performed by doing inverse gated NMR spectra on a final form of the resin. The development of this technique required the determination of the longitudinal relaxation times (T1) of the species within the melamine reaction as these were required to derive the necessary repetition rates employed in the NMR acquisition methods. \nIn general, this project involved the development of the above mentioned NMR analytical protocols with tailoring to run this type of experiment in a 5 mm NMR tube using a 400 MHz NMR spectrometer whereby previous research on urea and phenol formaldehyde resins and employing identical NMR methodologies had relied on analyses conducted in a 10 mm NMR tube on a 300 MHz NMR instrument. \nAs a result, reaction profiles of the melamine resin reaction were obtained during a real time experiment. The reaction profiles of the addition stage of the melamine resin reaction showed that the increase in the methylol melamine species occurs very fast and is justified by the exponential decay of the methylene glycol species corresponding to the formaldehyde solution. The condensation stages of the resin reaction were also observed until the IRE. The reaction profiles of the ether and methylene bridge links are clearly given showing that ether linkages predominate in the addition stage and plateaus, and methylene linkages only increase after the addition stage of the reaction. They provided insight to the reaction progress corresponding to addition and condensation stages of the melamine resin reaction.