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.
Step-growth polymerization via C–H activation is an attractive technique due to its advantages such as atom- and step-economy, derived from the reduced the number of synthetic steps required for the overall process and elimination of organometallic byproducts. To expand the utility of C–H activation polymerization beyond C–C bond coupling, we recently developed a highly efficient direct C–H amidation polymerization (DCAP) involving C–N bond formation, as a green polymerization process for synthesizing polysulfonamides. Here, we present a full account of the use of DCAP in the preparation of a library of polysulfonamides and polyamide from various diamides and diazides. From extensive model studies, several directing groups were screened, and it was found that subtle design of the directing groups by altering the steric hindrance and chelating bond angle greatly affected the efficiency of C–H amidation. Five directing groups were selected and seven AA-type monomers and seven BB-type monomers of azides were designed. After optimizing the polymerization process, 25 examples of well-defined high-molecular-weight (up to 171.4 kDa) polysulfonamides and polyamide were prepared. Notably, even diamide monomers containing four reactive ortho-C–H bonds produced defect-free polysulfonamides without cross-linking, supported by 1H NMR spectroscopy and size exclusion chromatography (SEC) traces. Furthermore, many of these polysulfonamides emitted light via an excited-state intramolecular proton transfer (ESIPT) process as a result of tautomerization upon photoexcitation.
We report a powerful strategy for activation of C-H bonds to produce polysulfonamides by an atom-economical and green method using iridium-catalyzed direct C-H amidation polymerization (DCAP). After screening various directing groups, additives, silver salts, concentrations, and temperatures to optimize DCAP, high-molecular-weight (up to 149 kDa) and defect-free polysulfonamides were synthesized from various bis-sulfonyl azides. Although these polymers do not have conventional fluorescent conjugated cores, they emit blue light with large Stokes shifts and high quantum yields upon photoexcitation owing to an excited-state intramolecular proton-transfer process.
Precise size control of semiconducting nanomaterials from polymers is crucial for optoelectronic applications, but the low solubility of conjugated polymers makes this challenging. Herein, we prepared length-controlled semiconducting one-dimensional (1D) nanoparticles by synchronous self-assembly during polymerization. First, we succeeded in unprecedented living polymerization of highly soluble conjugated poly(3,4-dihexylthiophene). Then, block copolymerization of poly(3,4-dihexylthiophene)-block-polythiophene spontaneously produced narrow-dispersed 1D nanoparticles with lengths from 15 to 282 nm according to the size of a crystalline polythiophene core. The key factors for high efficiency and length control are a highly solubilizing shell and slow polymerization of the core, thereby favoring nucleation elongation over isodesmic growth. Combining kinetics and high-resolution imaging analyses, we propose a unique mechanism called crystallization-driven in situ nanoparticlization of conjugated polymers (CD-INCP) where spontaneous nucleation creates seeds, followed by seeded growth in units of micelles. Also, we achieved “living” CD-INCP through a chain-extension experiment. We further simplified CD-INCP by adding both monomers together in one-shot copolymerization but still producing length-controlled nanoparticles.
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