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The aim of this investigation is to ascertain whether the mode of action of melamine in exible polyurethane (PU) involves condensed phase chemistry in terms of promoting char formation. A combination of in situ 1 H NMR analysis, solid state 13 C NMR characterization of chars prepared ex situ, and normal TGA and DSC has been employed. Solid state 13 C 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 1 H NMR provides de®nitive evidence that melamine acts in the condensed phase in terms of promoting the formation of rigid char which forms in more signi®cant 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 1 H NMR analysis which also involves fairly slow heating.

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