Nonstoichiometric Direct Arylation Polymerization for Synthesis of Naphthalenediimide-Based π-Conjugated Polymer

High-molar-mass π-conjugated polymers (CPs) are essential for semiconductor applications. However, conventional step-growth cross-coupling polymerizations generally require strict monomer stoichiometry according to the Carothers/Flory theory. Herein, an environmentally benign nonstoichiometric direct arylation polymerization (DArP) is reported that efficiently affords high-molar-mass CPs without employing metal-containing monomers or silver salts. Specifically, 3,4-ethylenedioxythiophene is polymerized using up to a 3-fold excess of 4,9-dibromo-2,7-bis(2-decyltetradecyl)benzo[lmn][3,8]-phenanthroline-1,3,6,8-tetraone in the presence of catalytic Pd₂(dba)₃/(4-dimethylaminophenyl)di-tert-butylphosphine (AmPhos), affording polymers with number-average molar masses far exceeding the theoretical values predicted using the Carothers/Flory equation. Model reactions involving 2,3-dihydrothieno[3,4-b][1,4]dioxine-5-carbonitrile and 4,9-dibromo-2,7-bis(2-hexyl)benzo[lmn][3,8]-phenanthroline-1,3,6,8-tetraone indicate that the electron-rich AmPhos ligand promotes intramolecular Pd catalyst transfer ("ring-walking"), enabling high polymerization efficiency even under nonstoichiometric conditions. The resulting polymers exhibit negligible structural defects and good solubility in common organic solvents, suggesting regioselective polymerization with minimal side reactions. The proposed nonstoichiometric DArP approach may offer advantages such as reduced polymerization times by using excess monomers that are readily accessible to high-performance semiconducting polymers.