This study aims at characterizing in depth the microstructure of propylene-co-1-pentene-co-1-hexene terpolymers, which have been recently reported to develop the isotactic polypropylene trigonal polymorph when the total comonomer content is high enough. Such a specific crystalline form had been only reported so far in the analogous copolymers containing either 1-pentene or 1-hexene. A comparative C-13 NMR study in solution of the aforementioned terpolymers and copolymers allows asserting the random insertion of both comonomers during chain growth under the polymerization conditions used. The reaction parameters, mainly catalyst and temperature, have been chosen for the purpose of assuring relatively high molar mass polymers. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2537-2547