Transetherification of melamine-formaldehyde resin methyl ethers and competing reaction of self-condensation

Transetherification of methyl ethers of melamine-formaldehide resins (MER) with monophenyl ethers of ethylene glycol or propylene glycol (ROH) and competing reaction of self-condensation are studied depending on MER composition (amounts of CH3O-, -CH2OH, and NH2 groups), ROH type, MER/ROH molar ratio, presence or absence of acid catalysts, and temperature. High rates of self-condensation processes prevent a complete conversion of CH3O-into RO-groups. It turned out MER free of methylol groups were not able to be transetherified with high yields due to a premature gelation taking place prior to attaining 50% conversion of methoxy groups (similar to 4 mol/kg) even at low MER/ROH ratios. In contrast, transetherification of MER with methylol groups content up to 3 mol/kg affords the incorporation of RO-groups into the resin up to 8 mol/kg owing to direct etherification of -CH2OH groups. The following factors are responsible for the growth of etherified product yield: presence of methylol groups in MER in some amounts without deterioration of MER-ROH compatibilization; CH2O-/ROH molar ratio no higher than 1; primary alcohols (ROH) is more preferable compared to secondary ones; thermal activation of the process is more efficient in comparison with acidic catalysis. (c) 2006 Wiley Periodicals, Inc.