| Considerable research has been put into the development of semiconducting poly(3-hexylthiophene) for use in flexible, all-organic photovoltaics. Its combination of relatively high thermal and environmental stability, high charge mobility, low band gap, and high solubility have made it a promising candidate organic electronics. Since the development of a chain-growth polymerization method by the Yokozawa group, control over molecular weight and regioregularity has increased the performance of devices based on this material significantly. Later, the development of an ex situ initiation method for P3HT synthesis has expanded the library of possible initiator molecules greatly.;The influence of alkyl-group stabilization of the propagating Ni(II) complex in P3HT is reported. Via synthesis of a monomer with halogens reversed from the often-used monomer, exploration of how the presence of an alkyl chain ortho to the terminal Br affects the polymerization. It was discovered that in the formation of a highly regioregular P3HT molecule, head-to-head additions are largely prevented by steric hindrance, and presence of an alkyl chain ortho to a Ni(II) complex serves to stabilize it, which is crucial to chain-growth polymerizations.;Four polymers of varying chain lengths were prepared by external initiation from a fullerene-containing initiator molecule and subsequent addition to activated monomer solution. 1H NMR end-group analysis indicates that the polymers are near the desired chain length, but the exact identity of these polymers has not yet been made clear.;Finally, highly regioregular P3HT of varying molecular weight (15, 25, and 35 kDa) was synthesized using both an external initiation method and the Yokozawa method. Regioregularities up to 99.6% were achieved, with good control over molecular weight, polydispersity, and end groups. Polymer films were investigated by UV-Vis absorption, X-ray diffraction, and differential scanning calorimetry; results show increased development of interchain crystalline structures for very highly regioregular P3HTs. This further increased crystallinity presents the opportunity to further increase the electronic properties of P3HT by maximizing regioregularity of the polymers. |
