This invention provides chain extender compositions. These compositions comprise (i) an aromatic primary diamine, and (ii) a component selected from the group consisting of: (a) an aliphatic secondary diamine; (b) an aliphatic primary diamine; (c) an aliphatic secondary diamine and an aliphatic primary diamine; (d) a diimine; and (e) a combination of any two or more of (a) through (d). When (ii) is (a), (a) has amino hydrocarbyl groups which are secondary or tertiary hydrocarbyl groups; when (ii) is (d), and (d) is an aromatic diimine, each imino hydrocarbylidene group has at least two carbon atoms. Processes for producing polyurethanes, polyureas, and polyurea-urethanes are also provided.