The present invention relates to a method for producing polyisocyanates comprising iminooxadiazinedione groups, wherein at least one monomeric di- and/or tri-isocyanate is oligomerized in the presence of at least one catalyst and succinonitrile. The invention relates further to a reaction system for producing polyisocyanates comprising iminooxadiazinedione groups, and to the use of succinonitrile in the production of polyisocyanates comprising iminooxadiazinedione groups by catalyzed modification of monomeric di- and/or tri-isocyanates.