| 摘要 |
1417087 Methylene bridged polyphenyl polyisocyanates IMPERIAL CHEMICAL INDUSTRIES Ltd 3 May 1974 [29 May 1973] 25370/73 Heading C2C A multiplicity of isocyanate compositions are prepared from a polyisocyanate mixture of methylene bridged polyphenyl polyisocyanates containing 40 to 85% by weight of diphenylmethane diisocyanates and made by phosgenation of a mixture of polyamines obtained by condensation of aniline and formaldehyde, by (a) distilling the polyisocyanate mixture and removing 5 to 70% by weight of the diisocyanate as volatile overhead (Product II) leaving a residue of methylene bridged polyphenyl polyisocyanates (Product I) and (b) submitting Product II to crystallization whereby there is obtained a crystallizate of 4,4<SP>1</SP>-diphenylmethane diisocyanate (Product III) and a mother liquor (Product IV) comprising 10 to 55% by weight of 2,4<SP>1</SP>-diphenylmethane diisocyanate and 90 to 45% by weight of 4,4<SP>1</SP>-diphenylmethane diisocyanate. |
