End-functionalized, regioregular poly(3-hexylthiophene) (P3HT) was synthesized by a combination of a controlled polymerization technique and postpolymerization functionalization. Both ends of the polymer chains were terminated with fullerene units to create an internal electron accepting−donating−accepting molecule, methylfulleropyrrolidine−poly(3-hexylthiophene)−methylfulleropyrrolidine (C60-P3HT-C60). The molecular properties of the polymer were characterized using 1H NMR spectroscopy, size exclusion chromatography (SEC), ultraviolet−visible (UV−vis) absorption spectroscopy, and fluorescence spectroscopy. These results show that the fullerene units are covalently bound to the polymer chain ends. Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS) were used to determine the bulk microstructure of the polymers. In addition, atomic force microscopy (AFM) was used to examine spun-cast thin films. These experiments revealed that microphase sepa...