Polyurethane/ureas useful for the production of spandex and a process for their production

1. A segmented polyurethane/urea produced by reacting in solution:

a) an isocyanato-terminated prepolymer having a free isocyanate group content of from about 1.0 to about 3.75% which is the reaction product of

(1) a stoichiometric excess of at least one diisocyanate with

(2) an isocyanate-reactive component comprising:

(i) a diol component which comprises

(a) at least 50 equivalent percent of at least one polyoxypropylene diol having a molecular weight of at least 1500 Da and an average unsaturation level less than or equal to 0.015 meq/g, and

(b) up to 50 equivalent percent of at least one polytetramethylene ether glycol having a molecular weight of at least about 600 Da and, optionally,

(ii) one or more other materials containing at least one functional group that is reactive with an isocyanate group, provided that the sum of the equivalent weight percents of (i) and (ii) is 100 equivalent percent, with

b) a chain extender comprising at least one asymmetric aliphatic and/or cycloaliphatic diamine and at least one linear diamine in the presence of

c) a solvent.

2. The polyurethane/urea of claim 1 in which from about 50 to about 90 equivalent percent of the diol component is the polyoxypropylene diol.

3. The polyurethane/urea of claim 1 in which the polyoxypropylene diol has an average molecular weight of from about 2000 to about 8000 Da.

4. The polyurethane/urea of claim 1 in which from about 50 to about 75 equivalent percent of the diol component is the polyoxypropylene diol.

5. The polyurethane/urea of claim 1 in which the diisocyanate is diphenylmethane diisocyanate.

6. The polyurethane/urea of claim 1 in which a catalyst was present during production of the prepolymer.

7. A spandex fiber spun from the polyurethane/urea of claim 1 .