Abstract
Field desorption mass spectrometry has been used to analyze chemical structures of constituent molecules and reaction mechanism in methylated methylol melamine resins. In the mass spectra of these resins synthesized under the different ratio between formaldehyde and melamine (F/M), many molecular and fragment ions corresponding to various degrees of methylolation and methylation have been observed respectively as shown in Fig. 2-6. The mass numbers of molecular and fragment ion peaks in table 2 could make it easily clear to estimate chemical structures of melamine derivatives containing methylol and methylated methylol groups and their distribution in the resins.
These mass spectra have shown directly the reaction mechanism under some reacting conditions. Namely, in initial step of reaction with melamine, formaldehyde and methy alcohol, F/M had influence on the degree of methylolation, and products in higher F/M reaction contained derivatives with more methylated structures. Moreover, low methylated derivatives were main products in this step. In second step with the initial products and methyl alcohol, methylation proceeded to be high methylated derivatives for main products. At the same time, poly melamine condensates were produced with melamine derivatives containing methylol group and free NH group as shown in chemical equation (1). This reaction was in proportion to the concentration of free NH groups. It might be suggested that methylol groups connected to melamine were dissociated to leave NH groups as shown in equation (2) and that poly melamine condensates increased consequently in sccond step reaction with initial products of lower F/M.
Through only one measurement by field desorption mass spectrometry, we could identify these molecular species and get some information about the molecular weight distribution. Therefore we can use this procedure effectively to analyse the reaction mchanism of melamine resin formation further.
