Abstract: The present invention relates to a process for the production of trimerized polyisocyanates containing at least 30 mole % of iminooxadiazinedione groups (asymmetric trimers) in the trimer mixture by catalytically trimerizing a starting isocyanate selected from organic di- or polyisocyanates having a number average molecular weight of 140 to 600 and containing aliphatically, cycloaliphatically and/or araliphatically bound isocyanate groups in the presence of quaternary ammonium and phosphonium fluoride trimerization catalysts corresponding to the formulaR.sub.4 E.sup.+ F.sup.- (I),whereinE represents N or P andR represents identical or different, optionally branched, aliphatic, aromatic and/or araliphatic C.sub.1 -C.sub.

Abstract: The present invention relates to a process for the preparation of trimerized polyisocyanates that contain at least 30 mole % of iminooxadiazinedione groups (asymmetric trimers) in the trimer mixture, by catalytically trimerizing a starting isocyanate selected from organic di- or polyisocyanates having a number average molecular weight of 140 to 600 and containing aliphatically, cycloaliphatically and/or araliphatically bound isocyanate groups in the presence of a quaternary phosphonium polyfluoride trimerization catalyst corresponding to the formulaR.sub.4 P.sup.+ F.sup.- n(HF)whereinR represents identical or different, optionally branched aliphatic, aromatic and/or araliphatic C.sub.1 -C.sub.20 groups, or two or more R groups may also form, with one another and with the phosphorus atom, saturated or unsaturated rings andn has a value of 0.1 to 20.