pi-Conjugated Copolymers of Controlled Sequence

Chapter 1 provides an introduction to pi-conjugated copolymers. Conjugated polymers are an increasingly important class of materials because of their potential application in electronic devices. Little is known about the effect of copolymer constitutional sequence because these materials have been synthetically inaccessible. Now pi-conjugated copolymers with varying sequences may be prepared through the newly discovered Ni-catalyzed living chain-growth polycondensation. Though several block and random copolymerizations have been reported, significant challenges remain in developing sophisticated pi-conjugated copolymer architectures such as gradient copolymers. This thesis our details efforts in discovering and understanding controlled copolymerizations.;Chapter 2 describes the development of a living, chain-growth copolymerization of 3-hexylthiophene and 3-(hexyloxy)methylthiophene. Monomer reactivity ratios were measured and revealed that the growing polymer chain has little preference for either monomer. The first conjugated gradient copolymers were prepared. Random and block copolymers were also synthesized and the copolymer sequence was found to influence the solid-state properties of the copolymers.;Chapter 3 details studies on cross-propagation between 3-alkylthiophene and 2,5-dialkoxybenzene monomers to determine mechanisms of catalyst dissociation during copolymerization. The effect of ligand electronics on block copolymerization was investigated and found to have little influence on copolymerization. Small-molecule model reactions indicated that catalyst dissociation does not occur due to a difference in pi-binding affinity between 3-alkylthiophene and 2,5-dialkoxybenzene units.;Chapter 4 describes extension of controlled copolymerization to new monomer pairs. The Kumada coupling copolymerization of 9,9-dioctylfluorene and 2,5-(bishexyloxy)benzene was investigated and batch copolymerizaions were found to exhibit chain-growth behavior. However the large difference in monomer reactivity ratios limited the gradient copolymer sequences accessible by batch methods. Semi-batch copolymerizations proved to be challenging because chain-growth behavior was found to depend on the total concentration of monomer. Ni(dppp)Cl2 catalyzed block copolymerizations of N-hexylpyrrole and 3-hexylthiophene displayed efficient cross-propagation. However, batch copolymerizations did not display chain-growth behavior.;Chapter 5 provides conclusion on the synthesis of conjugated copolymers and insights on controlled copolymerizations. The results reported herein suggest that improvements in catalyst and monomer design are necessary to increase the scope of controlled copolymerization.