Synthesis of a functionalized and photodegradable fluorene-based polymer for aqueous SWNT dispersion

Abstract

Due to their tunability, conjugated polymers have received significant interest in the dispersion of single-walled carbon nanotubes (SWNTs). Indeed, interactions with conjugated polymers enable simultaneous solubility, extraction, and purification of carbon nanotubes. However, due to the strong π-interactions between the carbon nanotubes and the polymer backbone, the polymer remains at the surface and can decrease the performance of a SWNT-based device. Therefore, the removal of the polymer backbone post-processing is a promising alternative. Here, we report the synthesis of a functionalized and photodegradable fluorene-based polymer. The polymer contains an ortho-nitrobenzylether linker that can be cleaved by irradiation using UV light. The irradiation was first investigated on the monomer and polymer by UV-Vis and ¹H-NMR spectroscopy and showed efficient degradation over time. Irradiation of the polymer-SWNT complex has also been investigated. Precipitation of the nanotubes upon irradiation was observed and confirmed the effective degradation of the polymer into smaller fragments. Characterization post-irradiation of the SWNT residues using thermogravimetric analysis was performed to quantify the proportion of polymer removed from the surface of the nanotubes. In addition, the synthesized fluorene-based polymer has azide groups at the end of the side-chains. We therefore functionalized the polymer with hydrophilic side-chains to disperse SWNTs in water. The photodegradation of the polymer was observed via UV-Vis spectroscopy and the polymer was efficient at dispersing SWNTs in the aqueous solvent. This work demonstrates the use of a functionalizable and degradable polymer allowing dispersion of SWNTs in various solvents by using a single polymer backbone as the dispersing agent.