Controlled Synthesis of Conjugated Polymers in Catalyst-transfer Condensation Polymerization: Monomers and Catalysts

This chapter describes the controlled synthesis of π-conjugated polymers by “living” chain-growth condensation polymerization through intramolecular catalyst transfer, i.e. catalyst-transfer condensation polymerization (CTCP). The first description of CTCP was in the Kumada–Tamao coupling polymerization of bromothienylmagnesium chloride with a Ni catalyst to afford well-defined poly(3-hexylthiophene). The mechanism of polymerization was intensively studied and growth was shown to proceed in a bidirectional manner. Many other π-conjugated polymers – such as polyphenylene, poly(N-alkylpyrrole), polyfluorene, poly(cyclopentadithiophene), poly(benzotriazole), and polythiazole – were obtained in a controlled manner. Functional Ni initiators were developed and allowed the introduction of functional groups at the chain end of the π-conjugated polymers. CTCP was extended to Suzuki–Miyaura reactions with a Pd catalyst. Well-defined polyfluorene, polyphenylene, polythiophene, polyphenanthrene, and poly(fluorene-alt-benzothiadiazole) were obtained. The combination of functional Pd initiators and end-capping boronic acids (esters) led to hetero end-functionalized π-conjugated polymers. Other coupling polymerizations, such as the Negishi coupling of Zn-containing monomers, Stille coupling of Sn-containing monomers, and Murahashi coupling of aryllithium monomers proceeded via the CTCP mechanism to yield well-defined π-conjugated polymers.