Process for preparing heat-resistant polyurethane elastomers having no secondary softening range

Claim 1

A process for the production of a castable heat-resistant polyurethane elastomer from primarily linear and substantially difunctional high-molecular-weight polyhydroxyl compound, polyisocyanate, and chain extender, characterized in that the high-molecular-weight polyhydroxyl compound is first reacted with such a quantity of polyisocyanate that the ratio of OH:NCO groups amounts to 1:0.66 to 1:0.85 to obtain an adduct of polyhydroxyl compound and an organic diisocyanate, which adduct is substantially anhydrous, and contains terminal hydroxyl groups, the adduct with terminal hydroxyl groups is then reacted with a diol as a chain extender and an excess of a symmetrical aromatic diisocyanate and with the provisos that the ratio of the number of isocyanate groups to the total number of all hydrogen atoms capable of reacting with the isocyanate groups amounts to approximately 1.0 to 1.2:1, and said chain extender forms a crystalline or crystallizable urethane with said aromatic diisocyanate, thereby obtaining a castable material exhibiting a start of softening at an advanced temperature of about 180° C. or greater.