<p>A polyurethane elastomer which comprises a reaction product of (A) a polymeric diol having a molecular weight of about 800-5000, (B) a mixture of organic diisocyanates wherein about 2-70 mol % is composed of aliphatic diisocyanate (said aliphatic diisocyanate having no direct bond between an aromatic ring and an isocyanate group) and wherein the balance 98-30 mol % is composed of aromatic diisocyanate which includes a direct bond between an aromatic ring and an isocyanate group, and (C) a chain extender comprising hydrazine and/or a derivative having the formula NH2NHR and another chain extender having two functional groups constituting amino and/or hydroxyl groups, and wherein about 30-80% of the carbon atoms which are bonded to nitrogen atoms constituting the ureylene and/or urethane bonds of said polyurethane elastomer constitute benzene and/or naphthalene ring skeletons. and wherein about 2-70% of the ureylene bonds of said polyurethane elastomer are formed by the reaction of aliphatic diisocyanate and hydrazine and/or its derivative having the formula NH2NHR.</p>
