Process for the production of uretdione polyisocyanates with improved monomer stability

A process for the production of polyisocyanates containing uretdione groups comprising the steps of

• oligomerizing a portion of the isocyanate groups of a starting diisocyanate with aliphatically and/or cycloaliphatically bonded isocyanate groups in the presence of a tertiary phosphine,
• terminating the oligomerization reaction at a desired oligomerization level and removal of the non-converted excess starting diisocyanate by extraction or thin-layer distillation,
• characterized in that the oligomerization reaction is carried out in the presence of ureas of formula (I) and/or amides of formula (II),
• wherein
• R1, R2 and R3 represent independently of one another a hydrogen atom, a saturated or unsaturated aliphatic or cycloaliphatic, an optionally substituted aromatic or araliphatic group, which may contain up to 18 carbon atoms and optionally up to 3 hetero atoms selected from oxygen, sulfur, nitrogen,
• R4 has the meaning given for R1 to R3 or represents the group
• wherein X represents a divalent, optionally branched, aliphatic or cycloaliphatic group with up to 12 carbon atoms, and R1 has the meaning given above,
• or
• R1, R2 and R3 in formula (I), and
• R1 and R4 in formula (II) in combination with each other together with the nitrogen atoms of the urea or amide group, and optionally a further nitrogen atom or an oxygen atom can also form heterocyclic rings with 3 to 6 carbon atoms.