This invention provides chain extender compositions. These compositions comprise (i) an aliphatic secondary diamine, and (ii) a component selected from the group consisting of: (a) a cycloaliphatic primary diamine; (b) an aliphatic secondary diamine; (c) an aliphatic secondary diamine and an aliphatic primary diamine; (d) an aliphatic diimine; and (e) a combination of any two or more of (a) through (d), with the proviso that when (ii) is (a), (i) is a noncyclic aliphatic secondary diamine. Processes for producing polyurethanes, polyureas, and polyurea-urethanes are also provided.