The effect of molecular weight on the supramolecular interaction between a conjugated polymer and single-walled carbon nanotubes

The synthesis and fractionation of poly[2,7-(9,9-dioctylfluorene)-alt-2,5-(3-dodecylthiophene)] resulted in the isolation of eight different molecular weight (Mw) samples ranging from Mn of 5 to 85 kg mol−1. These individual polymer samples were fully characterized by Gel Permeation Chromatography, Nuclear Magnetic Resonance, as well as absorption and fluorescence spectroscopy. Each sample was separately mixed and ultrasonicated with single-walled carbon nanotubes (SWNTs) in tetrahydrofuran, and the nanotube concentration within the resulting solutions was measured. It was found that the solubility of the polymer–SWNT complexes strongly depends on the Mw of the conjugated polymer, with a maximum concentration reached when Mw ranged between 10 and 35 kg mol−1. Higher and lower Mws resulted in substantially reduced nanotube concentrations.