PURPOSE: To isolate a trinuclear compound in a high yield and in a high purity, while reducing the by-production of tar, by subjecting a methylene-cross-linked polyphenylene polyisocyanate mixture to the combination of specific separation methods comprising specified operation conditions.
CONSTITUTION: A methylene-cross-linked triphenylene triisocyanate of the formula wherein n is 1 is isolated from the mixture of methylene-cross-linked polyphenylene polyisocyanates of the formula wherein n is 0 or a positive integer. Namely, most of diphenylmethane diisocyanate compound contained in the mixture is distilled off or evaporated off with a thin film evaporator. Subsequently, the methylene-cross-linked triphenylene triisocyanate is isolated and purified with a thin film evaporator. Or a methylene-cross-linked polyphenylene polyisocyanate fraction containing the diphenylmethane diisocyanate and the methylene-cross-linked triphenylene isocyanate as main components is obtained from the mixture with the above-mentioned device, and the diphenylmethane diisocyanate is distilled off from the low boiling point fraction.
TAKASAKI MICHIYA
SHIMAMATSU MITSUNORI
IIJIMA MASAAKI
SATO NAOKI
MIYATA KATSUJI
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