Foamed polyurethanes and their preparation

A one-step method for preparing a rigid foamed polyurethane in situ on a surface comprises applying to the surface an organic polyisocyanate or polyisothiocyanate and as the sole or major hydroxyl group containing component an active polyol, and an organic nitrogen compound containing at least one primary or secondary amino group and at least one hydroxyl group, a 1,1,3,3-tetra-alkyl-guanidine as catalyst and a foaming agent that is a gaseous organic compound, a volatile organic liquid or water, the amount of organic nitrogen compound being at least 5% of the combined weight of active polyol and organic nitrogen compound. The term "active polyol" is defined as a polyalkylene ether polyhydroxy compound containing at least three hydroxyl groups and which by virtue of its mode of preparation, contains in a given weight thereof a higher proportion of primary hydroxyl groups than the same weight of a polyalkylene ether polyhydroxy compound of comparable equivalent weight prepared by condensing a low M.W. polyhydroxy compound with a 1,2-epoxy compound other than ethylene oxide in the presence of a non-acidic condensation catalyst. Suitable active polyols are those prepared by condensing a low M.W. polyhydroxy compound, e.g. glycerol, with a 1,2-epoxy compound, other than ethylene oxide, in the presence of an acidic condensation catalyst or by effecting condensation with a non-acidic catalyst provided the resulting condensation product is further reacted with ethylene oxide to satisfy the above condition or by condensing a low M.W. polyhydroxy compound with ethylene oxide using any suitable condensation catalyst. Conventional polyisocyanates and polyisothiocyanates may be use, but diisocyanato- or diisothiocyanato-diaryl methanes are preferred. The preferred organic nitrogen compounds are dialkanolamines especially those wherein each hydroxyalkyl radical contains from 2 to 4 carbon atoms, and the preferred 1,1,3,3-tetraalkylguanidine is 1,1,3,3-tetramethylguanidine. The foamable compositions may also contain a trialkylamine, a tin salt of an aliphatic carboxylic acid and a foam stabilizer. Preferred foaming agents are water or an organic compound which is liquid or gaseous at 0 DEG C., e.g. trichlorofluoromethane. The foamable composition is usually sprayed on to a suitable surface either by bringing the separate components together in a mixing device and then spraying or by mixing two components (a) the active polyol, organic nitrogen compound and guanidine deri