Verfahren zur Herstellung flüssiger Diphenylmethandiisocyanate

摘要

A process for preparing a liquid MDI, which comprises adding, to MDI, a phosphorin catalyst and a phosphorous acid ester of the formula (I): or the formula (II): wherein R<1>, R<2>, R<3>, R<4>, R<5>, R<6> and R<7> each is, same or different, and C4-C20 alkyl group, and conducting a reaction. EFFECT: The process according to the present invention can produce liquid MDI having stable properties. This liquid MDI has almost no discoloring, even if it is stored for a long time. The present process can commercially provide a polyurethane raw material having an easy handling.