Methods of preparing rigid polyurethane foams, and precursor compositions therefor

This invention is directed to a process for preparing a rigid polyurethane foam which comprises reacting a polyisocyanate with polyol in the presence of a blowing agent, a polymerization catalyst and a surfactant. The polyol has the fnrmula:wherein R1, R2, and R3 are, each independently, hydrogen, a C1 - C6 alkyl group, bearing one or more halogen, hydroxyl, optionally substituted phenyl, optionally substituted cycloalkyl, or optionally substituted phenyl ether substituents, n is 1 or 2, and x + y + z is from 3.5 to 6. Rigid polyurethane foams produced by this process show a reduced degree of friability.