A series of ester derivatives of the bicyclic phosphate 4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-1-oxide has been prepared via its reactions with acid anhydrides, or, in the case of the methacrylate ester, via reaction with methacryloyl chloride. With an excess of diketene, the bicyclic phosphate is converted into the related acetoacetate ester, which forms an aluminium salt on reaction with aluminium isopropoxide. Only those derivatives having a free, ionisable hydrogen undergo intumescent decomposition on heating. The effects of variation in the structure of the melamine base component of a series of salts of a dialkylphosphoric acid derived from the bicyclic phosphate on thermal stability and intumescent behaviour have also been studied. With trimethylolmelamine, a highly insoluble, thermally stable salt has been obtained which exhibits marked intumescence on thermal decomposition and which imparts fire-retardance on incorporation into polyester, polypropylene and polyurethane systems. The structure of the intumescent foam derived from this salt has been compared with that generated under identical conditions from the related melamine salt, the former leading to the formation of a denser foam with smaller cells. © 1994.
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