The relationships between the structure and properties have been established for copolymers of propylene and 1-hexene synthesized with an isotactic metallocene catalyst system. The most important factor affecting the structure and properties of these copolymers is the comonomer content. The thermal treatment, that is, the rate of cooling from the melt, is also important. These factors affect the thermal properties, the degree of crystallinity, and therefore the structural parameters and the viscoelastic behavior. A slow cooling from the melt favors the formation of the gamma phase instead of the alpha modification. Regarding the viscoelastic behavior, the beta relaxation, associated with the glass-transition temperature, is shifted to lower temperatures and its intensity is increased as the 1-hexene content raises. The microhardness values are correlated with those of the storage modulus deduced from dynamic mechanical thermal analysis curves, and good linear relations have been obtained between these parameters. (c) 2006 Wiley Periodicals, Inc.