Solid state 13C and in situ 1H NMR study on the effect of melamine on the thermal degradation of a flexible polyurethane foam

The aim of this investigation is to ascertain whether the mode of action of melamine in flexible polyurethane (PU) involves condensed phase chemistry in terms of promoting char formation. A combination of in situ 1H NMR analysis, solid state 13C NMR characterization of chars prepared ex situ, and normal TGA and DSC has been employed. Solid state 13C NMR indicates that there is no major discernible difference in the structure of the dichloromethane‐insoluble chars prepared with and without melamine, the remaining polyol only accounting for 20–25 % of the total carbon at 350 °C, but still being quite mobile. However, in situ 1H NMR provides definitive evidence that melamine acts in the condensed phase in terms of promoting the formation of rigid char which forms in more significant quantity by 450 °C. No increase in the residue yields is observed by TGA upon melamine addition, probably due to a combination of the small sample size and open sample holder in relation to the in situ 1H NMR analysis which also involves fairly slow heating. © 2000 Society of Chemical Industry