Abstract: This disclosure provides compositions containing isocyanate and isocyanurate groups by allowing a pMDI to react in the presence of a trimerization catalyst, and the process for producing a rigid PUR/PIR foam from this composition. The disclosure further relates to the process for producing the compositions containing isocyanate and isocyanurate groups, to the production of rigid PUR/PIR foams from these compositions, to the rigid foams themselves, and to the use of such rigid foams.

Abstract: The present invention relates to a one-component reaction system for producing hard polyurethane foams, comprising the following constituents: A) an organic polyisocyanate component which is partially or entirely in prepolymer form, B) an isocyanate-reactive component, the functional groups of which are exclusively those having at least one Zerewitinoff-reactive hydrogen atom and optionally having at least one halogen atom, C) at least one stabilizer, D) at least one catalyst suitable for catalysing the reaction of the polyisocyanate component A) with the isocyanate-reactive component B), and E) optionally auxiliaries and additives and blowing agents and co-blowing agents, the reaction system being characterized in that the content of monomeric polyisocyanate is at most 1% by weight, and in that the organic polyisocyanate component A) has an isocyanate content of less than 8% by weight relative to the polyisocyanate component A).