| 摘要 |
The acidity and hydrolyzable chloride levels of polymethylene polyphenyl polyisocyanates are reduced (and the reactivity correspondingly increased) by exposing the polyisocyanate, in solution in inert organic solvent, to heating at a temperature of 150 DEG C to 230 DEG C and under a pressure in the range of 20 psia to 60 psia with removal of volatile overhead. The process can be carried out continuously or in a batch procedure. The polyisocyanate so treated, in addition to lowered acidity and hydrolyzable chloride, is found to be substantially free of impurities which give rise to offensive odors when the polyisocyanate is employed in the preparation of flexible foams. |
