Polyurethanes with narrow-disperse (ND) and polydisperse (PD) hard segment (HS) distributions were prepared in a two-step process. First, a poly(propylene oxide) end-capped with MDI (4,4methylenebis(phenyl isocyanate) was synthesized. To this prepolymer either a diamine-diamide was added to form ND HSs or a mixture of a diamine-diamide and additional MDI to form PD HSs in the copolymers. The polyurethanes displayed a ribbon-like crystalline morphology, and it was found that the copolymers with ND HSs were more crystalline, had a higher modulus, a less temperature-dependant modulus, and a higher melting temperature than their PD counterparts. Overall, the polyurethanes with the narrow-dispersed HSs displayed superior properties.