Process for the preparation of oligomeric polyisocyanates and their use

The present invention relates to a process for the preparation of oligomeric polyisocyanates in which (a) a portion of the isocyanate groups of organic polyisocyanates is oligomerized in the presence of catalysts that accelerate the dimerization of isocyanate groups, and (b) the oligomerization reaction is terminated after reaction of about 5 to about 45% of the isocyanate groups present in said organic polyisocyanates by the addition of a catalyst poison comprising a silylated acid corresponding to the formula X-[Si(CH3)3]n wherein X represents the neutral acid residue obtained by removal of the acidic hydrogen atoms from an n-basic acid having a pKa value of at most 3, other than a hydrohalic acid, and n is an integer of 1 to 3. The invention also relates to the use of oligomeric polyisocyanates obtained by this process, optionally in admixture with unreacted starting polyisocyanates and/or optionally with the isocyanate groups blocked by blocking agents, as polyisocyanate component for the preparation of polyurethane resins by the isocyanate polyaddition process.