Six novel polyureas were prepared from benzimidazolin-2-one and benzimidazolin-2-thione, which acted as hard segments, with two aromatic diisocyanates (4,4'-diphenylmethane diisocyanate and toluene 2,4-diisocyanate) and one aliphatic diisocyanate (hexamethylene diisocyanate). The polymers that formed were fully characterized with Fourier transform infrared spectroscopy, C-13-NMR cross-polarization/magic-angle spinning, differential scanning calorimetry, and thermogravimetry. X-ray diffraction revealed that the polymers contained crystalline and amorphous regions that varied with the nature of the backbone structures. All the polyureas were insoluble in common organic solvents, and this made it difficult to investigate their solution properties. (c) 2006 Wiley Periodicals, Inc.