Abstract: The present invention is directed to a process for the production of a mono- and/or polyisocyanate by the phosgenation of a mono- and/or polyamine in a mixer which comprises(a) a casing having at least two inlets and at least one outlet,(b) a rotatable shaft extending through the casing,(c) at least one rotor disc attached to the shaft such that the rotor disc is perpendicular to the shaft,(d) at least one stator disc attached to the casing such that the stator disc is parallel to the rotor disc and has an opening such that the shaft can pass through the stator disc,(e) optionally at least one running wheel attached to the shaft and containing openings such that when the shaft is rotating the running wheel provides a pumping effect to the reaction mixture passing through the mixer,(f) at least one inlet through the casing for introducing a phosgene solution axially to the shaft and against the rotor disc,(g) at least one inlet through the casing for introducing a mono- and/or polyamine amine solution or suspe

Abstract: The present invention is directed to the stabilization of a prepolymer based on methylene diphenyl isocyanate rich in the 2,4'-isomer. It was surprisingly found that the color stability, viscosity and aging characteristics of the prepolymer are improved markedly upon the incorporation therewith of a combination of a certain epoxide compound and a hindered phenol.