Chapter 2: Controlled Chain-growth Synthesis of Conjugated Polymers: Moving Beyond Thiophene

The controlled chain growth synthesis of polythiophenes has led to astounding progress in controlling the composition, morphology, and properties of conjugated polymers. This has allowed researchers to use polythiophenes in fundamental studies and as functional materials for advanced electronic applications. Until recently, controlled chain growth polymerization methods were limited to small, electron-rich heterocycles such as thiophenes, selenophenes, pyrroles, and phenylenes. The current generation of high-performance conjugated polymers are copolymers consisting of alternating electron-rich and electron-deficient monomers that are significantly different from thiophene in both chemical and electronic structure. The ability to synthesize such polymers with control over sequence and composition remains an important goal, however, and new synthetic methodologies need to be developed to achieve this. We outline recent advances in applying controlled chain growth polymerization methods to monomer types commonly found in high-performance conjugated polymers. Well-defined homopolymers, statistical copolymers, and block copolymers consisting of electron-rich and electron-deficient aromatic units are beginning to be synthesized in a controlled manner. As a result of these advances, characterizing the effects of structure, composition, and sequence on the morphology, phase separation, and electronic properties of these polymers is a burgeoning field of research.