Producing method of polyurethane and/or preformed polymer

In the production of a diphenylmethanedi-isocyan ate fraction containing at least 99 wt% binuclear di-isocyanate by reaction of aniline and formaldehyde followed by phosgenation and separation, the crude product is worked up by removal of some or all of the 2,2'-MDI to give a fraction containing 0-0.4 wt% 2,2'-MDI, 1-95 wt% 4,4'MDI and 5-98.6 wt% 2,4'-MDI. - A method for the production of a diphenylmethanedi-isocyanate (MDI) fraction (I) containing at least 99 wt% binuclear MDI, involves (a) acid-catalysed reaction of aniline and formaldehyde to give di- and poly-amines, (b) phosgenation (optionally in solvent) to give crude di- and poly-isocyanate, (c) separation to give a faction containing at least 95 wt% binuclear MDI with a 4,4'-MDI content of 49-95.99 wt%, a 2,4'-MDI content of 4-45wt% and a 2,2'-MDI content of 0.01-20 wt%, (d) optional removal of 10-98 wt% of the 4,4'-MDI and (e) removal of some or all of the 2,2'-MDI to give a fraction containing 0-0.4 wt% 2,2'MDI, 1-95 wt% 4,4'-MDI and 5-98.6 wt% 2,4