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<p>Non-metallic cationic polymerization of low-reactivity styrene (St) derivatives remains challenging due to broad molecular weight distributions and rapid deactivation of active species. Here we show that adding only a minor amount of CH<sub>3</sub>CN (<i>V/V</i>, 3/97) to the conventional BF<sub>3</sub>·OEt<sub>2</sub>/COH/CH<sub>2</sub>Cl<sub>2</sub>/St system affords polystyrene with narrow dispersity (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub>, Đ ≈ 1.3). Notably, the <i>M</i><sub>n</sub> increases linearly with conversion and closely matches the <i>M</i><sub>n.calcd</sub>. <sup>1</sup>H-nuclear magnetic resonance (<sup>1</sup>H-NMR) analysis and comparative experiments with the BF<sub>3</sub>·CH<sub>3</sub>CN co-initiation system indicate CH<sub>3</sub>CN does not coordinate strongly with BF<sub>3</sub> compared to diethyl ether (OEt<sub>2</sub>); however, it stabilizes the propagating carbocation and decreases the the propagation rate constant (<i>k</i><sub>p</sub>), which leads to a narrower dispersity in the product. Lowering the temperature to −25 °C further extends the active-chain lifetime. This strategy is also effective for other low-reactivity styrene monomers, including <i>p</i>-chlorostyrene (<i>p</i>ClSt) and <i>p</i>-chloromethylstyrene (<i>p</i>CMSt), and is even applicable to the relatively more reactive <i>p</i>-methylstyrene (<i>p</i>MeSt), offering a versatile metal-free route to the synthesis of styrenic polymers with a narrow dispersity.</p>

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A Paradigm for BF3 co-initiated Cationic Polymerization with Low Dispersity: Introducing Acetonitrile and Lowering the Reaction Temperature

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Yi-Meng Liu,
  • Yu Zhu,
  • Bo-Yu Xu,
  • Zi-Lin Xu,
  • Xing-Long Zhang,
  • Hui Li,
  • Qiang Liu,
  • Shou-Ke Yan

摘要

Non-metallic cationic polymerization of low-reactivity styrene (St) derivatives remains challenging due to broad molecular weight distributions and rapid deactivation of active species. Here we show that adding only a minor amount of CH3CN (V/V, 3/97) to the conventional BF3·OEt2/COH/CH2Cl2/St system affords polystyrene with narrow dispersity (Mw/Mn, Đ ≈ 1.3). Notably, the Mn increases linearly with conversion and closely matches the Mn.calcd. 1H-nuclear magnetic resonance (1H-NMR) analysis and comparative experiments with the BF3·CH3CN co-initiation system indicate CH3CN does not coordinate strongly with BF3 compared to diethyl ether (OEt2); however, it stabilizes the propagating carbocation and decreases the the propagation rate constant (kp), which leads to a narrower dispersity in the product. Lowering the temperature to −25 °C further extends the active-chain lifetime. This strategy is also effective for other low-reactivity styrene monomers, including p-chlorostyrene (pClSt) and p-chloromethylstyrene (pCMSt), and is even applicable to the relatively more reactive p-methylstyrene (pMeSt), offering a versatile metal-free route to the synthesis of styrenic polymers with a narrow dispersity.