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.