Terpolymers based on propylene with 1-pentene and 1-heptene as comonomeric units are satisfactorily synthesized containing distinct overall compositions in comonomers as well as three different 1-pentene/1-heptene ratios at a given global composition. The effect of total content in counits and ratio between comonomers on polymerization activity, intrinsic viscosity, molecular weights and microstructural details has been analyzed. In addition, their influence on the mechanical response has been preliminary checked. The results show that rigidity related parameters, like Young's modulus and yield stress, are mainly dependent on overall composition, but comonomer ratio becomes also a primary variable for the terpolymers with a global counit content higher than 10 mol %. This fact is ascribed to the capability or inability of developing the trigonal polymorph as function of which counit (1-pentene or 1-heptene) is in majority or minority. (C) 2016 Elsevier Ltd. All rights reserved.