The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X-ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well-defined conformation as, for example, expressed in the formation of lyotropic liquid-crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well-defined macromolecular conformation is observed. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725-1736, 2003.