US 10,131,736 B2  15  16  (Formula IV)  and x-is selected from the group consisting of p-, HF$_{2 }$ -,  H$_{2}$F$_{3 }$-and mixtures thereof.  2.  The process according to claim  1,  wherein the acid  corresponding to the anion x-has a pKa2:2.5.  3.  The process according to claim  1  wherein the oligomer› ization is conducted in the presence of a solvent or an  additive.  4.  The process according to claim  1,  wherein the mono› meric organic isocyanate comprises one or more aliphatic  diisocyanates.  5.  The process according to claim  1,  wherein the process  is conducted within the temperature range from 0° C. to  +250°  C.  6.  The process according to claim  1,  wherein the oli› gomerization is stopped after about 5% to about 80% by  weight of the monomeric organic isocyanate used has been  converted.  7.  The process according to claim  6,  wherein the oli› gomerization is stopped by deactivating the catalyst.  8.  The process according to claim  6,  wherein unconverted  monomeric organic isocyanate is separated from the reaction  mixture.  9.  The process according to claim  2,  wherein the acid  corresponding to the anion x-has a pKa2:3.0.  10.  The process according to claim  2,  wherein the acid  corresponding to the anion x-has a pKa2:3.10.  11.  The process according to claim  4,  wherein the one or  more aliphatic isocyanates is/are selected from the group  consisting ofhexamethylene diisocyanate (HDI), 2-methyl› pentane 1,5-diisocyanate, 2,4,4-trimethylhexane 1,6-diiso› cyanate, 2,2,4-trimethylhexane 1,6-diisocyanate, 4-isocya› natomethy !octane  1,  8-diisocyanate, 3(  4)  -isocyanatomethyl- 1-methy lcyclohexy  l  isocyanate (IMCI), isophorone diiso- cyanate (IPDI), 1,3- and 1,4-bis(isocyanatomethyl)benzene  (XDI),  1,3- and  1,4-bis(isocyanatomethyl)cyclohexane  (H6XDI) and mixtures thereof.  12.  The process according to claim  5,  wherein the process  is conducted within the temperature range from about 20 to  about 180°  C.  13.  The process according to claim  5,  wherein the process  is conducted within the temperature range from  40  to 150°  C.  14.  The process according to claim  6,  wherein the oli› gomerization is stopped after about  10%  to about 60% by  weight of the monomeric organic isocyanate used has been  converted.  15.  The process according to claim  7,  wherein the deac› tivation comprises adding an acid or an acid derivative, an  acidic ester of phosphorus- or sulfur-containing acids to  adsorptively bind the catalyst and removing the catalyst by  filtration.  *  *  *  *  * 