Scope of controlled synthesis via chain-growth condensation polymerization: from aromatic polyamides to pi-conjugated polymers

Conventional condensation polymerization proceeds in a step-growth polymerization manner, in which the generated polymers possess a broad molecular weight distribution, and control over molecular weight and polymer end groups is difficult. However, the mechanism of condensation polymerization of some monomers has been converted from step-growth to chain-growth by means of activation of the polymer end group, either due to the difference in substituent effects between the monomer and the polymer, or due to successive intramolecular transfer of catalyst to the polymer end. In this article, we review recent developments in chain-growth condensation polymerization (CGCP) in these two areas. The former approach has yielded many architectures containing aromatic polyamides and aromatic polyethers, with unique properties. In the latter case, the mechanism, catalysts, and initiators of Ni- and Pd-catalyzed coupling polymerizations leading to poly(alkylthiophene)s and poly(p-phenylene) s have been extensively investigated. Other well-defined pi-conjugated polymers, such as polyfluorenes, n-type polymers, and alternating aryl polymers, have also been synthesized by means of catalyst-transfer condensation polymerization. Many pi-conjugated polymer architectures prepared by utilizing catalyst-transfer condensation polymerization are not covered in this article.