A process for producing a polycarbodiimide, comprising polymerizing a diisocyanate in the presence of a carbodiimidization catalyst in a reaction vessel in liquid phase at a temperature in the range of from 20 to 250° C., at a pressure in the range of from 20 to 800 mbar and in the presence of at least one inert gas, wherein the at least one inert gas is introduced into the liquid phase in the reaction vessel with a flow rate in the range of from 0.1 x/h to 100 x/h, x being the volume of the reaction vessel.