Preparation of cast elastomers using aminocrotonate-terminated polyether chain extenders

A process for preparing polyurethane elastomers comprising reacting in an open mold at an isocyanate index of 90 to 110

• (a) an isocyanate prepolymer having an isocyanate content of 2 to 15% by weight and having a molecular weight of from 500 to 5000, wherein said isocyanate prepolymer is a reaction product of
• (i) at least one organic polyisocyanate with
• (ii) at least one isocyanate-reactive compound having at least two isocyanate-reactive groups and having a molecular weight of from 1000 to 3000;
• with
• (b) an aminocrotonate-terminated polyether having a molecular weight of from 500 to 1500 and having the formula ##STR3## wherein A is the m-functional group left by the removal of the hydroxyl groups of a polyether polyol having a molecular weight of from 150 to 800,
• R is the difunctional residue of an organic diamine having the formula H.sub.2 N-R-NH.sub.2 such that each free -NH.sub.2 group of the aminocrotonate-terminated polyether (b) has a sufficiently moderated reactivity toward isocyanate prepolymer (a) to allow the preparation of a polyurethane elastomer in an open mold, and
• m is a number of from 2 to 8;
• and
• (c) 0 to about 10 percent by weight, relative to aminocrotonate-terminated polyether (b), of a chain extender and/or crosslinker other than aminocrotonate-terminated polyether (b) and having two isocyanate-reactive hydrogen atoms and a molecular weight of from 32 to 250;
• optionally in the presence of
• (d) one or more catalysts and/or other auxiliaries or additives.