Abstract

In a process for the trimerization of diisocyanates in the presence of a catalyst comprising quaternary ammonium salts of organic acids having the formula: ##STR1## wherein X represents the same or different radicals selected from the group consisting of C1 -C20 alkyl, C3 -C8 cycloalkyl, and C2 -C20 aralkyl; two X radicals taken together with at least one other heteroatom forming a hetero-ring and three X radicals taken together with the quaternary nitrogen atoms forming a hetero-ring through a common hetero-atom such that said heterocyclic ring structure is selected from the group consisting of triethylene diamine, methyl triethylene diamine, quinuclidine, N-methylmorpholine, N-ethylmorpholine, and N,N'-dimethylpiperazine; R is alkyl, cycloalkyl or aralkyl, R" is R or hydrogen; R+R" together form a C1 -C12 alkyl radical; R' is hydrogen, hydroxyl or a C1 -C12 alkyl radical, optionally containing a CH.sub.(3-b) Zb group, wherein b=1 to 3 and Z is OH, the improvement comprising: reacting said diisocyanate with said catalyst in an amount of 0.02 to 0.1% by weight calculated on the weight of the compound to be trimerized at a temperature ranging from 40° to 120° C.