Method for production of new, thermal and chemical resistant polyurethane plastics, particularly in the form of foams, these foams being obtained from the reaction of di- or poly- isocyanates with polyols, said polyols having the formula 1 or 2 as herein described, Ar in the said formulas representing a benzene, naphthalene or anthracene ring, which may be singly or multiply substituted with a halogen atom, alkyl radical, aryl radical or allyl radical, Z representing the oxygen atom, a group SO.sub.2 or a divalent radical --CRR.sub.1 -- where R and R.sub.1 represent a hydrogen atom or an alkyl radical, m and r represent 0 or 1, and n and p represent an integer 1-10, or their mixtures with other low-viscosity polyols or with a compound having formula 3 as herein described in which R.sub.2 represents a simple or branched alkyl or aryl radical which can be substituted by a lower alkyl or aryl radical or by halogen atoms added in a quantity of 0.1-50 parts by weight, these being reacted with isocyanates or in the presence of catalysts, foaming agents and solvents.