Wide-angle X-ray scattering has been employed for evaluation of the crystal structure of cold-crystallized random copolymers of propylene with 1-butene. The crystallization procedure included the formation of a metastable mesophase at ambient temperature by quenching the quiescent melt, and the reorganization of the semimesomorphic structure into a semicrystalline structure on subsequent heating/annealing. Research was performed to gain information about incorporation/exclusion of 1-butene chain defects into the crystalline phase when formed via the intermediate step of mesophase formation. The X-ray data suggest that 1-butene co-units up to a concentration of at least 11 mol-% are incorporated into both the mesophase formed on quenching and crystals formed on subsequent heating/annealing according to their concentration in the chain. This observation is in agreement with results obtained on samples which were crystallized directly from the supercooled liquid state, indicating that incorporation of 1-butene co-units into the crystalline phase is not kinetically controlled. Furthermore, information about the alpha/gamma polymorphism and the kinetics of the transition from the semimesomorphic into semicrystalline structure are provided. (C) 2010 Elsevier Ltd. All rights reserved.