(Third Place Poster Award) Synthesis and Characterization of Block Copolymer Dispersants for Semiconducting Single-Walled Carbon Nanotubes

Abstract

To leverage the full potential of the outstanding electronic properties of semiconducting single-walled carbon nanotubes (s-CNTs), it is essential to disperse and sort high purity s-CNTs from a heterogeneous mixture. Due to the inherent insolubility of CNTs, various organic dispersing agents that non-covalently interact with CNTs have been successfully used. These dispersants include small molecule surfactants and aromatic compounds, conjugated polymers, DNA, and polyelectrolytes. Of the macromolecular dispersants, polymers with conjugated backbones are widely studied because they can wrap around or strongly adsorb on CNTs to create very stable dispersions in organic solvents. Most of these conjugated polymers are based on polythiophenes or polyfluorenes, which depending on the structure and composition can sort specific chiralities of s-CNTs with over 99.99% semiconducting purity.In this work, we explore conjugated polymer-based block copolymers for sorting and dispersing s-CNTs. Non-conjugated block copolymer-based dispersants have been reported by us and others with varying degrees of success in aqueous and organic solvents. Here we present our recent studies on the synthesis of ABA triblock copolymer-based CNT dispersants where B is the conjugated block and A is the non-conjugated block. The synthesis of the ABA triblock can be achieved by separately synthesizing the rod segments and the coil segments, each with reactive chain end functionalities, and then coupling the rod segments with the coil segments via reaction of the chain ends using, for example, a click reaction. Alternatively, the rod segment or the coil segment can be synthesized first and used as a macroinitiator for the polymerization of the other segment. Each of these two methods offers some advantages and disadvantages. A series of these ABA triblocks with fixed B block length and varying A block lengths were synthesized and evaluated for their ability to sort and disperse ArcD and HiPCO CNTs. A second series of ABA triblocks with fixed A block lengths but increasing B block lengths were also synthesized. We will present the challenges associated with the synthesis and purification of these block copolymer dispersants. As the middle-conjugated B block wraps around the CNTs, we anticipate the two peripheral A blocks to interact with the organic solvent toluene to further solubilize the CNTs. Our studies show that the presence of the A blocks significantly increases the sorting efficiency while preserving the chirality selectiveness of the B block. As the length of the B block increases, the sorting yields can be significantly improved as well. We further discuss the role of the dispersity of the B block if any on the dispersion of s-CNTs.