Abstract: An isocyanate-terminated prepolymer C having an NCO content of from ?26% by mass to ?31.0% by mass is obtainable from the reaction of an isocyanate composition A having a viscosity at 25° C. of from ?60 mPas to ?800 mPas, comprising from ?25% by mass to ?60% by mass MDI and from ?40% by mass to ?75% by mass pMDI, wherein the sum of the amounts of those components is ?100% by mass, with a bifunctional polyester ether polyol B having an OH number of ?200 mg(KOH)/g and ?500 mg(KOH)/g, obtained from the reaction of a dicarboxylic acid/dicarboxylic acid derivative with at least one polyol and with an epoxide, wherein the polyester ether polyol B is used in amounts of from ?1.5% by mass to ?6.0% by mass, based on the sum of the masses of A and B. The invention further provides a PUR/PIR polymer produced from the prepolymer C, its use and composite elements based thereon.

Abstract: An isocyanate-terminated prepolymer C having an NCO content of from ?26% by mass to ?31.0% by mass is obtainable from the reaction of an isocyanate composition A having a viscosity at 25° C. of from ?60 mPas to ?800 mPas, comprising from ?25% by mass to ?60% by mass MDI and from ?40% by mass to 75% by mass pMDI, wherein the sum of the amounts of those components is ?100% by mass, with a bifunctional polyester ether polyol B having an OH number of ?200 mg(KOH)/g and ?500 mg(KOH)/g, obtained from the reaction of a dicarboxylic acid/dicarboxylic acid derivative with at least one polyol and with an epoxide, wherein the polyester ether polyol B is used in amounts of from ?1.5% by mass to ?6.0% by mass, based on the sum of the masses of A and B. The invention further provides a PUR/PIR polymer produced from the prepolymer C, its use and composite elements based thereon.