Fundamental understanding of microphase separation in ABC miktoarm copolymers is vital to access a plethora of nonconventional morphologies. Miktoarm stars based on poly(cis 1,4-isoprene) (I), poly(styrene) (S), and poly(2-vinylpyridine) (V) are model systems, which allow systematic studies of the effects of composition, chemical microstructure, and temperature on the thermodynamics of microphase separation. Eleven ISV-x (I:S:V = 1:1:x, v:v:v) miktoarm copolymers were synthesized by anionic polymerization affording well-defined copolymers with a variable V arm. Equilibrium bulk morphologies of all samples, as evidenced by small-angle X-ray scattering, transmission electron microscopy (TEM), and self-consistent field theory, showed a systematic transition from lamellae (x approximate to 0-0.2) to [8.8.4] tiling (x approximate to 0.6-0.9) to cylinders in undulating lamellae (x approximate to 2-4) and, finally, to hexagonally packed core-shell cylinders (x approximate to 5-8). Chemical microstructure of the I arm [poly(cis 1,4-isoprene)] versus poly(3,4-isoprene) is shown to play important role in affecting morphological behavior. To reconcile differences between ISV-x star morphologies reported in the literature and those reported herein, even for the same composition, effects of the microstructure of I arm on the Flory-Huggins parameter between I and V arms were taken into account in a qualitative manner. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1491-1504