Solid state C-13 and in situ H-1 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 (HNMR)-H-1 a nalysis, solid state (CNMR)-C-13 characterization of chars prepared ex situ , and normal TGA and DSC has been employed. Solid state (CNMR)-C-13 indicat es that there is no major discernible difference in the structure of the di chloromethane-insoluble chars prepared with and without melamine, the remai ning polyol only accounting for 20-25 % of the total carbon at 350 degreesC , but still being quite mobile. However, in situ (HNMR)-H-1 provides defini tive evidence that melamine acts in the condensed phase in terms of promoti ng the formation of rigid char which forms in more significant quantity by 450 degreesC. No increase in the residue yields is observed by TGA upon mel amine addition, probably due to a combination of the small sample size and open sample holder in relation to the in situ (HNMR)-H-1 analysis which als o involves fairly slow heating. (C) 2000 Society of Chemical Industry.