Three segmented copolymers having as hard segments poly(urethane-urea)s based on isophorone diisocyanate (IF) and 1,4-benzenedimethanol (B) and having as soft segments poly (dimethylsiloxane)s (PDMS) of three different molecular weights are analyzed by CP-MAS C-13-NMR. Comparison of cross-polarized and non-cross-polarized spectra, together with proton relaxation measurements, establishes the presence of separated phases and differences in their mobility. The T-1p(H)’s and static H-1-NMR half-height line widths of PDMSyK-IP-B-2 (y = 2.4, 10, and 27; refers to the PDMS molecular weight) give information about the motion as a function of the molecular weight of PDMS. A dipolar filter sequence is employed to estimate the size of the dispersed hard phases, which appears to be of about 5 nm for all samples. The overall (soft and hard) domain sizes increase with the increase of silicone molecular weights, as expected.