Reversible Functionalization of Single-Walled Carbon Nanotubes by Switchable Conjugated Polymers

Abstract

Single-walled carbon nanotubes (SWNTs), since their first discovery in early 1990s, have drawn enormous research attention owing to their extraordinary properties. These excellent optical, electrical, thermal and mechanical properties have enabled SWNTs to make profound impacts in the field of nanotechnology, which includes nanoscale nanoelectronics, chemo-/biosensors, photovoltaics, drug delivery, and advanced nanocomposite materials. However, the as-produced SWNT samples contain a mixture of metallic and semiconducting SWNTs, amorphous carbon, and metal catalyst particles. Also, due to π-π stacking and van der Waals forces, pristine SWNTs tend to form bundles, making them insoluble in most of organic solvents. The poor processibility and purity hinder the direct use of as-produced SWNTs as the material for fabrication of SWNT-based devices. Therefore, the post-synthesis purification is highly required. Conjugated polymers have proven to be efficient SWNT dispersants, but after solution processing, conjugated polymers adhered to the sidewall of SWNTs can not be easily removed and thus negatively affect the performance of the resulting SWNT-based electronic devices. Therefore, polymers that can dissociate from the surface of SWNTs after solution processing is highly desirable. Apart from the introduction to several other efficient purification methods of SWNTs, Chapter 1 also gives a brief review on reversible functionalization of SWNTs by polymers. The work reported in the literature categorized by the different external stimuli used to reverse the polymer-SWNT association. Chapter 2 describes the design and synthesis of a vinylogous tetrathiafulvalene (TTFV)-based conjugated polymer, which is responsive to pH changes and thus realized reversible functionalization of SWNTs. Chapter 3 describes the design and synthesis of dithiafulvenyl-grafted phenylene ethynylene polymers, which can reversibly interact with SWNTs by changing solvents. Chapter 4 describes the design and synthesis of dithiafulvene (DTF)-based electron-rich conjugated polymers, which can selectively bind with semiconducting SWNTs. In addition, Chapter 5 describes the use of SEC to achieve high-resolution separation, and isolation of surfactant-free metallic and semiconducting SWNTs. This allowed us to study the competition behavior when different ratios of metallic and semiconducting nanotubes are used as the starting material for polymer dispersions. Finally, Chapter 6 describes a side project that involves covalent functionalization of GO using Piers-Rubinsztajn reaction. The functionalized GO is loaded into silicone elastomer to reduce the air permeability and enhance the mechanical strength of the resulting silicone elastomer.