| 摘要 |
<p>Polyisocyanates of the diphenyl methane series having reduced color values are obtained by a) reacting aniline and formaldehyde in the presence of an acid catalyst to form a polyamine, b) neutralizing the reaction mixture containing polyamine with a base, c) separating the neutralized mixture into the aqueous and the organic phases, d) adding a base to the organic phase and then e) phosgenating the resulting polyamine to produce the corresponding polyisocyanate.</p> |
