The stereo-electronic control over bisadditions of conjugated polymers to fullerene (C-60) is explored in the formation of alternating copolymers. The chemistry, resulting configuration, and properties of poly(3-hexylthiophene)-alt-C-60 copolymers prepared by either classic pyrrolidine ring formation or an atom transfer radical addition are compared. Both routes result in controlled additions of polymers to C-60. Extensive macromolecular modeling through PM6 methods indicate that there is no conjugation between P3HT and C-60 in the systems studied. This along with 2D-NMR, AFM, and photovoltaic characterizations of the materials indicate the importance of the structure of the modified C-60 and the nature of the linking group between C-60 and P3HT segments in determining the morphology of the copolymers in the solid state. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 23042317,2009