Two series of well-defined poly(urethane urea) multiblock copolymers were synthesized to investigate the phase-separated morphology of this family of materials. Series I copolymers were synthesized from 2000 g/mol, poly(tetramethylene oxide) [PTMO], 4,4'-methylene di(p-phenyl isocyanate) [MDI], and ethylenediamine (EDA), with hard segment contents ranging from 14 to 47 wt %. Series II copolymers (all with hard segment concentrations of 22 wt %) were prepared from the same PTMO and MDI and a diamine mixture of EDA and 1,4-diaminocyclohexane. The microdomain morphology was characterized using small-angle X-ray scattering, and the scattering data were analyzed using the approach of Bonart and Muller. The series I and II copolymers were found to have relatively low overall degrees of phase separation [ranging from similar to 20% at the lowest hard segment contents to greater than 40%], contrary to the common nation that these copolymers are well phase separated materials. The introduction of the second diamine results in reduced phase separation; presumably as a consequence;of disruption of hard segment hydrogen bonding.