Process for the preparation of uretdione group containing polyisocyanates

A process for the preparation of uretdione group containing polyisocyanates, comprising reacting monomeric aromatic diisocyanates selected from the group consisting of 1,5-naphthalenediisocyanate, 1,4-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, polymethylenepolyphenylenepolyisocyanate, 2,4- and 2,6-toluenediisocyanate, 2,2'-, 2,4'-, and 4,4'-diphenylmethane diisocyanate, and mixtures thereof in the presence of a catalyst wherein imidazoles or benzimidazoles having general structural formulas I or II are used as said catalysts;

• ##STR3## or mixtures thereof are used as said catalysts, whereby R.sup.1 and R.sup.5 independently are C.sub.1 - to C16- alkyl groups;
• alkenyl or alkynyl groups having 2 to 16 carbon atoms;
• aryl groups;
• alkylaryl or aralkyl groups, whereby the alkyl groups can have from 1 to 10 carbon atoms, amino groups;
• hydroxyl groups or mercapto groups;
• aminoalkyl groups;
• alkylamino groups;
• alkoxy groups;
• oxyalkyl, alkylthio groups or thioalkyl groups having C.sub.1 - to C16-alkyl groups or halogen atoms, R.sup.2, R.sup.3, R.sup.4, R.sup.6, or R.sup.7 have the same meaning as R.sup.1 and R.sup.5 or are nitro groups and R.sup.3, R.sup.4 can be hydrogen provided that R.sup.1 is not alkyl, alkenyl or alkynyl;
• with the proviso that the following compounds are excluded:
• 1-allyl-2-methylimidazole,
• 1,2-dimethylimidazole,
• 1-methylimidazole and
• 1-butylimidazole,
• wherein the reaction product contains less than about 2 weight percent isocyanurates.