A method to produce uretonimine-modified isocyanate composition comprises Providing an organic isocyanate composition having two or more isocyanate groups; Reacting, in the presence of a suitable catalyst, said polyisocyanate composition to form uretonimine-modified isocyanate composition comprising carbodiimide groups and uretonimine groups; terminating said reacting by the addition of an amount of oxalic acid mono alkyl ester halide.