| 摘要 |
A process for treating methylene-bridged polyphenylpolyamine mixtures prepared by the silica-alumina catalyzed condensation reaction of aniline and formaldehyde to obtain substantially pure low functionality Diaminodiphenylmethanes having increased 4,4'-positional isomer content and a higher functionality methylene-bridge polyphenylpolyamine mixture having a narrow molecular weight range is disclosed. A methylene-bridge polyphenylpolyamine mixture, prepared by the condensation reaction of aniline and formaldehyde carried out in the presence of a silica-alumina cracking catalyst, containing at least about 75 weight percent diaminodiphenylmethanes based upon the weight of the mixture and having a 4,4'-positional isomer content in the diamine portion of above about 65%, based upon the weight of the diamine portion, is admixed at a temperature of from about room temperature to about 150 DEG C. with a material capable of forming a solution with the mixture at the temperature employed. A portion of the admixture-solution is then allowed to crystallize and is separated therefrom, which comprises substantially pure diaminodiphenylmethane having a 4,4'-positional isomer content of above about 85 weight percent. The remainder of the admixture contains a methylene-bridged polyphenylpolyamine mixture of reduced diaminodiphenylmethane content and a narrow molecular weight distribution. Both portions can be employed as precursors in conventional phosgenation techniques to provide corresponding organic isocyanates which are highly useful in the preparation of certain coatings, elastomers, flexible and rigid forms and the like.
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