Synthesis of Azine-Based Conjugated Polymers by Metal-Free Dehydration Polycondensation and Characterization of Their Physical Properties

For application in organic electronic devices, conjugated polymer materials must be free of impurities such as catalyst residues and terminal functional groups that inhibit carrier transport. Pd-catalyzed cross-coupling polycondensation is a common synthesis method for producing conjugated polymer materials. Although the method is very reliable, it requires complete removal of Pd residues from the products to meet purity requirements. This study focused on the metal-free synthesis of conjugated polymers containing azine bonds in their main chains. The dehydration condensation of dialdehyde monomers and hydrazine was optimized, and the results revealed that a two-step reaction is effective for obtaining high-molecular-weight polymers. Pure materials were obtained through a simple purification procedure. Their molecular weight and terminal structures were arbitrarily controlled by adjusting the monomer ratio and adding end-capping reagents. The azine moiety in the main chain functioned as a weak acceptor unit and extended its conjugation by linking aromatic units with high planarity. The synthesized azine-based polymers with fused thiophene skeletons serve as p-type semiconducting materials for organic field-effect transistors and organic photovoltaics. These results provide fundamental and important insights on green synthesis and the application of azine-based conjugated polymers.