Catalyst-transfer polymerization has revolutionized the field of polymer synthesis due to its living character, but for a given catalyst system, the polymer scope is rather narrow. Herein we report a highly efficient Suzuki−Miyaura catalyst-transfer polymerization (SCTP) that covers a wide range of monomers from electron-rich (donor, D) to electron-deficient (acceptor, A) (hetero)arenes by rationally designing boronate monomers and using commercially available Buchwald RuPhos and SPhos Pd G3 precatalysts. Initially, we optimized the controlled polymerization of 3,4-propylenedioxythiophene (ProDOT), benzotriazole (BTz), quinoxaline (QX), and 2,3-diphenylquinoxaline (QXPh) by introducing new boronates, such as 4,4,8,8-tetramethyl-1,3,6,2dioxazaborocane and its N-benzylated derivative, to modulate the reactivity and stability of the monomers. As a result, PProDOT, PBTz, PQX, and PQXPh were prepared with controlled molecular weight and narrow dispersity (Đ < 1.29) in excellent yield (>85%). A detailed investigation of the polymer structures using 1 H NMR and MALDI-TOF spectrometry supported the chain-growth mechanism and the high initiation efficiency of the SCTP method. In addition, the use of RuPhos−Pd showing excellent catalyst-transfer ability on both D/A monomers led to unprecedented controlled D−A statistical copolymerization, thereby modulating the HOMO energy level (from −5.11 to −4.80 eV) and band gap energy (from 1.68 to 1.91 eV) of the resulting copolymers. Moreover, to demonstrate the living nature of SCTP, various combinations of D−A and A−A block copolymers (PBTz-b-PProDOT, PQX-b-PProDOT, and PQX-b-PBTz) were successfully prepared by the sequential addition method. Finally, simple but powerful one-shot D−A block copolymerization was achieved by maximizing the rate difference between a fast-propagating pinacol boronate donor and a slow-propagating acceptor to afford well-defined poly(3hexylthiophene)-b-poly(benzotriazole).

Herein, we report detailed mechanistic studies of Suzuki-Miyaura catalyst-transfer polycondensation (SCTP) of thiophene. The effects of boronates, halides, ligands, and chain transfer agents (CTAs) on the control of polymerization were systematically investigated in detail by SEC, 1H NMR and MALDI-TOF analyses. Initially, we identified that the use of the slow-hydrolyzing N-methyliminodiacetic acid (MIDA) boronate in place of conventional pinacol boronate effectively suppressed side reactions such as protodeboronation, homocoupling, and chain transfer reactions, thereby improving control of SCTP. Screening halides revealed that the monomer containing bromide was optimal for SCTP, resulting in less side reactions. Moreover, screening several ligands and adding a CTA further supported our conclusion that the RuPhos-Pd system showed the best catalyst-transfer ability among the tested catalysts. We further elucidated that externally added ligands effectively stabilized living chain-ends and suppressed chain transfer, thereby achieving controlled polymerization.

Despite the remarkable breakthroughs in the catalyst-transfer polymerization (CTP) technology in the precision synthesis of conjugated polymers, modulating the monomer reactivity is still challenging. We report that, by boronate tuning, we can modulate the rate of the Suzuki–Miyaura CTP (SCTP) of 3-hexylthiophene with high control. First, cyclic boronate esters showed different polymerization rates depending on their diol subunit structure. Additionally, the rates of the N-coordinated boronates were differentiated by tuning their O- or N-substituents. Notably, the origin of the difference in reactivity could be explained by the N → B bond lengths. The detailed structural analysis of the resulting polymers by 1H nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectrometry showed that the slower and more stable boronate monomers were less prone to homocoupling and protodeboronation, thereby producing poly­(3-hexylthiophene) (P3HT) with higher control (i.e., molecular weight, dispersity, end-group fidelity, and yield). By rational optimizations to suppress homocoupling and protodeboronation, well-defined P3HT were prepared at various monomer-to-initiator ratios (M/I ratios).