Producing (M1) 4,4'-methylenebis(phenylisocyanate) (MDI) dimer, comprises: (a) providing a solvent comprising a catalyst for 4,4'-methylenebis(phenylisocyanate) (MDI) with an inert gas atmosphere at greater than 25[deg] C to 45[deg] C; (b) adding a melted and/or dissolved MDI with stirring over a time span of 0.5-3 hours; (c) adding a deactivator, while stirring during addition over a time span of 0.5-1.5 hours at the given reaction temperature; (d) separating the obtained MDI dimer from the solvent; and (e) purification of the obtained MDI dimer with the solvent. An independent claim is also included for the 4,4'-methylenebis(phenylisocyanate) dimer (MDI dimer) obtained by the method (M1).