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相关概念视频

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)01:16

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
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Olefin Metathesis Polymerization: Overview01:13

Olefin Metathesis Polymerization: Overview

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Recently, the development of olefin metathesis polymerization advanced the field of polymer synthesis. Simply put, the reorganization of substituents on their double bonds between two olefins in the presence of a catalyst is known as the olefin metathesis reaction. The use of metathesis reaction for polymer synthesis is called olefin metathesis polymerization.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists...
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Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)00:53

Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)

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Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
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Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

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The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
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Radical Chain-Growth Polymerization: Mechanism01:09

Radical Chain-Growth Polymerization: Mechanism

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The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this...
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Ziegler–Natta Chain-Growth Polymerization: Overview01:17

Ziegler–Natta Chain-Growth Polymerization: Overview

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Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta...
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Updated: May 25, 2025

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers
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在封闭状态下进行环膨胀转化聚合

Patrick Probst1, Moritz Lindemann1, Johanna R Bruckner2

  • 1Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, Stuttgart 70569, Germany.

Journal of the American Chemical Society
|February 26, 2025
PubMed
概括
此摘要是机器生成的。

在有序的中等孔中固定复合物增强了环膨胀转化聚合. 这种限制可以合成具有受控立体选择性的低分子量循环聚合物.

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科学领域:

  • 有机金属化学
  • 聚合物化学
  • 材料科学

背景情况:

  • 使用过渡金属复合物的催化对于聚合物合成至关重要.
  • 将催化剂限制在多孔材料中可以改变反应性和选择性.
  • 订购的半孔 (OMS) 提供可调节的孔径,用于催化剂固定.

研究的目的:

  • 在OMS中固定一个阴阳性基基 (N-heterocyclic carbene (NHC)) 复合物.
  • 研究孔隙封闭对循环烯的环膨胀转化聚合物的影响.
  • 对聚合物分子重量和立体选择性的限制影响进行探索.

主要方法:

  • NHC复合物的合成和表征 [Mo(C-p-OMeC6H4) ((OCMe ((CF3) 2) ((IMes)) ] B ((ArF4).
  • 将复合物固定在具有不同孔径 (66,56,28 Å) 的 OMS 中.
  • 环膨胀转化聚合 (REMP) 的循环烯包括cis-cyclooctene (cCOE),1,5-cyclooctadiene (COD), (+) -2,3-endo,exo-dicarbomethoxynorborn-5-ene ((+) -DCMNBE),和2-methyl-2-phenylprop-1-ene (MPCP).
  • 使用矩阵辅助激光脱离离子飞行时间 (MALDI-TOF) 质谱分析聚合物产品.

主要成果:

  • 在 OMS 毛孔内选择性固定复合物.
  • 观察到对REMP的强烈限制效应,导致低分子量循环聚合物,即使在高单体度.
  • 通过MALDI-TOF确认了单独的循环聚合物的形成.
  • 限制诱导的Z选择性和cis-syndios特异性的增强.

结论:

  • 在OMS中限制NHC催化剂是控制REMP的有效策略.
  • OMS的孔隙大小显著影响聚合结果,使得具有定制性质的循环聚合物能够合成.
  • 这种方法提供了一种通过催化剂限制精确控制聚合物架构和立体化学的途径.