GB840500A - Process for the production of urethane polyisocyanates - Google Patents

Abstract

In a process of producing urethane polyisocyanates having a high content of available -NCO, but which do not emit toxic vapours, by reacting an organic di-isocyanate with a polyhydric alcohol, the proportions of the two reactants being such that there is more than 1 mol. of di-isocyanate for each hydroxyl group of the polyhydric alcohol whereby the formation of polymeric products of high molecular weight is minimized, the liquid reaction mixture is extracted, preferably at a temperature between 50 DEG C. and 130 DEG C., with a liquid aliphatic and/or alicyclic hydrocarbon, or a mixture of such hydrocarbons, in order to dissolve out unreacted di-isocyanate from the urethane polyisocyanate product. Hexanes, cyclohexane, the alkyl cyclohexanes, heptanes, octanes, gasoline fractions and synthetic hydrocarbon fractions are the preferred extraction media. In an example, a mixture of toluylene-2,4-di-isocyanate and toluylene-2,6-di-isocyanate is heated to 90 DEG C.; and a mixture comprising trimethylol propane and 1,3-butylene glycol is added over a period of 2 1/2 hrs. while maintaining the temperature at about 88 DEG to 100 DEG C. The resulting urethane polyisocyanate, dissolved in excess toluylene diisocyanate, is then extracted with a solvent (boiling range 315-390 DEG F.) comprising about 88% paraffins and naphthenes and about 11.5% aromatics. The extraction is carried out in an externally heated vertical column divided into seven sections, each containing a turbineagitator. The polyisocyanate is fed continuously into the top of the column, while the solvent is introduced into the bottom; the temperature of the column being held in the range of 100 DEG to 116 DEG C. The extracted product, withdrawn from the bottom of the column, is heated in vacuo to remove solvent. The final product is an amber solid which contains 18.5% available NCO. Other polyhydric alcohols which may be reacted with organic diisocyanates are: pentaerythritol, triethanolamine, neopentyl glycol, and castor oil. It is also possible to use, together with the polyhydric alcohol, a small amount of a higher-molecular polyhydroxy compound, such as hydroxyl polyesters or hydroxyl polyethers.