Polyether polyol for preparing rigid polyurethane foams

Polyether polyol having an aromaticity in the range of from 2% to 35%, an average nominal functionality (Fn) in the range of from 2.0 to 4.5 and a hydroxyl value in the range of from 390 to 650 mg KOH/g, whereby the aromatic carbon atoms are contained in structural moieties of the general formula wherein both R1 groups independently represent hydrogen or a C1-C3 alkyl group; both R2 groups independently represent a C1-C3 alkyl group; and n is an integer of from 0 to 3. Process for the preparation of the above polyether polyol, which process comprises reacting an alkylene oxide with a polyhydric alcohol blend comprising a diphenylol alkane precursor of the above indicated structural moiety and at least one aliphatic or alicyclic polyhydric alcohol having a functionality of at least 2.0. Polyether polyol blend having an aromaticity in the range of from 2 to 10% and a Fn in the range of from 2.5 to 5.0 eq/mole, which blend comprises the above polyether polyol and one or more aliphatic or alicyclic polyether polyols having a Fn of at least 2.5. Rigid polyurethane foam having a total aromaticity in the range of from 35% to 50%, obtainable by foaming a composition comprising the above polyol or polyol blend having an aromaticity from 2 to 10% and a Fn from 2.5 to 5.0 eq/mole, and an aromatic polyisocyanate in such amount that the isocyanate index is from 100 to 150, whereby the polyol reactant accounts for from 1 and 10% of the total aromaticity of the rigid polyurethane foam.