A carbon-13 solid-state NMR study was made of a set of model random ethylene copolymers, namely the hydrogenated polybutadienes. By adopting appropriate pulsing sequences, the different elements of phase structure were isolated and the characteristics of the crystalline, amorphous, and crystalline-amorphous interfacial regions were established. The relative amounts and the thicknesses were determined for each of these regions. The results obtained by the NMR method agree very favorably with those previously reported by Raman spectroscopy with identical copolymers.