The competition between a, beta, and ? polymorphs has been studied in several random copolymers and terpolymers of propylene, by performing X-ray diffraction and differential scanning calorimetry experiments. Formation of beta-crystals, achieved by the addition of a beta-nucleating agent, was found to be highly dependent on comonomer type and crystallization conditions. Additionally, the mechanical properties have been evaluated from stress-strain, microhardness and dynamic-mechanical thermal analyses. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers