Copolymers of propylene and 1-octadecene synthesized by a metallocene catalyst were characterized by PALS, WAXD, DSC, and density measurements. The change in the sizes and the number density of free-volume holes as a function of the 1-octadecene content were compared to the master laws published for copolymers of propylene with alpha-olefins of shorter lengths. It was found that the samples were separated into two groups. The first set of samples obeyed the master laws while the second group deviated. This behavior was explained by the difference in the copolymer structure. The WAXD analysis confirmed the separation as well. The deviation was explained as due to the mesomorphic crystalline structure of the second group of samples, in contrast to the monoclinic one for the first group, which was a result of the relatively fast cooling from the molten state and from the high comonomer molar content. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1994-2002, 2010