| 摘要 |
The instant invention is directed to a process for the continuous preparation of polyisocyanates containing uretdione groups comprising dimerizing aromatic polyisocyanates which are free from uretdione groups in the presence of catalysts which accelerate the dimerization of isocyanates, at -30 DEG to 90 DEG C. in a self-cleaning, coolable screw reactor with continuous feeding in of the free polyisocyanate and of the dimerization catalyst, and in the presence of from 3 to 90% by weight, based on the whole mixture, of an additive containing hydroxyl groups, which additive comprises either (i) a compound within the molecular weight range of from 62 to 10,000 containing at least one hydroxyl group or (ii) a mixture of several compounds having an average molecular weight within the range of from 62 to 10,000 containing at least one bound hydroxyl group, wherein said hydroxyl-containing compound or compounds are added to the reaction mixture before the isocyanate used as starting material solidifies due to the dimerization reaction.
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