The effect of the content of rigid blocks on the phase state and structure of rigid domains in segmented polyurethane based on polyethylenebutyleneglycol adipate, 1,4-butandiol, and 4,4′-diphenylmethane diisocyanate is studied with the aid of pulsed 1H NMR. It is shown from an analysis of free induction decays and using the Goldman-Shen technique that in the specimen having the minimum rigid block length a microphase is formed whose domains have sharp boundaries without intermediate regions. With increase in rigid block length, a second type of domain appears together with the first, consisting of a central part and an intermediate region of high molecular mobility. The ratio of the number of domains of different types depends on the temperature. The dimensions of the domains and intermediate regions are evaluated, and possible structural models are considered.