Foamed polyurethanes and their preparation

A one-step method for preparing a rigid foamed polyurethane in situ on a surface comprises applying to the said surface a polyurethane-forming foamable composition comprising an organic polyisocyanate or polyisothiocyanate and as the sole or major hydroxyl group-containing component an active polyol and an organic nitrogen compound containing in its molecular structure at least one primary or secondary amino group and at least one hydroxyl group, the amount of organic nitrogen compound being at least 5% by weight of the combined weight of the active polyol and the organic nitrogen compound. The equivalent weight of the hydroxyl-group containing component should be such that a rigid foamed polyurethane is formed by reaction with an organic polyisocyanate or polyisothiocyanate. An "active polyol" is defined as a polyalkylene ether polyhydroxy compound containing at least three hydroxyl groups in its molecular structure and which, by virtue of its mode of preparation, contains in a given weight a higher proportion of primary hydroxyl groups as compared with the same weight of "conventional" polyalkylene ether polyhydroxy compound of comparable equivalent weight. By "conventional" is meant those polyalkylene ether polyhydroxyl compounds which are normally used for making rigid foamed polyurethanes which are prepared by condensing a lower molecular weight polyhydroxy compound (e.g. glycerol) with a 1, 2-epoxy compound other than glycerol in the presence of a non-acidic catalyst. Suitable polyols are those prepared as a condensation product of a lower molecular weight polyhydroxy compound with a 1, 2-epoxy compound either (a) by using an acidic catalyst (e.g. boron trihalides, chlorides and bromides of aluminium, tin and titanium chlorides of antimony beryllium, bismuth cadmium, gallium, iron, zinc and zirconium and mineral acids) or (b) by reacting with ethylene oxide a polyalkylene ether polyhydroxy compound of intermediate molecular weight prepared using a non-acidic catalyst or (c) by using ethylene oxide as the 1, 2-epoxy compound. Water and/or volatile liquid foaming agents can be used. Suitable organic nitrogen compounds are mono- and di-alkanolamines and condensation products of alkylene oxides with amines or alkanolamines. In the mixture reacted to give a foam there may also be present catalysts such as tertiary amines, foam stabilizers, pigments, fire retardants (halogen compounds, organic or inorganic phosphates or borates, oxides of antimony, zinc or