Urethane elastomers are produced by initially adding at least one incremental amount of a curing agent to a urethane prepolymer, having free polyisocyanate therein. Generally, free polyisocyanate-curing agent adducts are precipitated. Subsequently, the remaining amount of curing agent is added. Chain extension, accordingly, is favored which produces hard segment domains more evenly distributed in the polymer chain and imparts improved physical properties such as hardness, tear strength and high-low strain modulus.