Abstract: The invention relates to a process for producing polyisocyanurate plastics having a functionalized surface, comprising the following steps: a) providing a polyisocyanate composition A) containing monomeric and/or oligomeric polyisocyanates; b) catalytically trimerizing the polyisocyanate composition A) so as to obtain a bulk polyisocyanurate material as intermediate; c) surface functionalizing the intermediate by contacting at least one surface of the intermediate with at least one functionalizing reagent D); d) continuing the catalytic trimerization. The invention further relates to a polyisocyanurate plastic having a functionalized surface obtainable from the process of the invention.