A chromatographic investigation into the reactions of urea and formaldehyde
A literature survey showed that very few studies into the chromatographic separation of urea formaldehyde resins have been made. Those that have been undertaken are of doubtful or limited value. A rapid reproducible method for investigating the molecular mass distribution of urea formaldehyde resins by size exclusion chromatography has been developed. By using lithium chloride in dimethylformamide as the solvent for chromatography, solubility and molecular association problems have been overcome. A novel liquid chromatographic procedure using an aminopropyl bonded silica column, having 8,000+ plates and acetonitrile/water as eluant has been developed. Using this technique some twenty simple low molecular mass urea-formaldehyde reaction products have-been separated efficiently and quickly. Using the novel chromatography, investigations of the reactions of urea and formaldehyde in the pH range 5.5 to 8.3 and molar ratio 1: 1.5 to 1: 2.5 demonstrated that dimethylene ether linkages were formed to a greater degree than simple methylene linkages. It has been shown that the ammonia formed by hydrolysis of urea was converted fistly into methylamine and subsequently into 1,3,5-triazin-4-ones structures. Tetrahydrol, 3,5-oxadiazin-4-ones (urons) have been shown to be formed very readily at high and low pH values (<2 and >10) Dimethyloluron has been obtained in the solid state for the first time and its physical properties studied. Four new uron compounds have been isolated and completely characterised. The reactions of dimethyloluron with urea and formaldehyde have been studied. The lack of reactivity of formaldehyde, when stabilised with a small amount of urea has been shown to be due to the formation of dimethyloluron.