Hydroxy compounds, polyol products

Some special derivatization methods that lead to the formation of cyclic products were recommended for alcohols with more than two hydroxyl groups in the molecule (polyols including carbohydrates), amino alcohols, and polyfunctional aromatic hydroxy compounds. An appropriate arrangement of two functional groups [(OH)2, (OH) + (NH2) or (OH) + (CO2H)] in 1,2 (vie) 1,3 or ortho (in aromatic series) positions is necessary for their realization (Table 8). 

The thermal decomposition, combustion, and fire retardancy of PU materials have been reviewed. " Upon heating, the polymer decomposes primarily by regenerating the precursor moieties polyols, isocyanates, and amines. Complete volatilization of the resulting products is prevented by the formation of thermally stable isocyanurate rings (produced by trimerization of isocyanates) and the formation of substituted ureas (produced by the reaction of hydroxy compounds with the carbodiimides generated by dimerization of isocyanates). ... 

As mentioned in Section 8.4.3.1., the majority of hydroxy groups in a polyether triol are secondary groups and are comparatively unreactive towards isocyanates. It is therefore necessary to select a catalyst which favours the formation of urethane links relatively more than the formation of gas by the reaction of isocyanate and water. Tin compounds (e.g., stannous octoate and dibutyltin dilaurate) are particularly effective in this respect (cf.. Table 14.3) and are very widely used. In addition to the primary isocyanate-polyol and isocyanate-water reactions, several secondary reactions occur during the preparation of foam. As shown in Section 14.4, the final product may contain allophanate, biuret, isocyanurate and uretidione links. It will be appreciated that in a polymeric system, which is based on a diisocyanate, all of these links (except uretidione) represent points of branching or cross-linking. These secondary reactions are particularly favoured by tertiary amines (e.g., triethylenediamine and 4-dimethylaminopyridine) and these catalysts therefore contribute to the final cross-linking of the foam and hence to the achievement of, for example, a low compression set. Mixtures of tin compounds and tertiary amines are more... 

---