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Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration02:34

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The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.
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The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
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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.
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Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)00:53

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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
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使用双态安萨-金属烯复合体对烯聚合物的对比效应.

Muqtar Mohammed1, Marcio Nele, Abdulaziz Al-Humydi

  • 1Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.

Journal of the American Chemical Society
|June 26, 2003
PubMed
概括
此摘要是机器生成的。

这项研究研究了使用金属催化剂和各种联合启动剂的烯聚合. 聚合物微观结构在很大程度上不受对子选择的影响,催化剂的行为主要因操作模式而异,而不是内在的立体选择性.

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科学领域:

  • 聚合物化学 聚合物化学
  • 有机金属化学 有机金属化学
  • 催化剂是一种催化剂.

背景情况:

  • 金属催化剂对于烯酸聚合至关重要,提供可调节的特性.
  • 了解共同发起者和对抗子对催化剂性能的影响,是控制聚合物微观结构的关键.
  • 烯聚合为研究复杂的催化机制提供了一个模型系统.

研究的目的:

  • 研究不同联合发起剂 (甲基氨酸,B(C(6) F(5)) ((3),[Ph(3) C][B(C(6) F(5)) ((4))) 对使用不对称的安萨-金属复合物的烯聚合物的作用.
  • 阐明催化剂结构,共同发起者和由此产生的聚烯 (PP) 微结构之间的关系.
  • 探索单体度对催化剂行为和聚合物战术性的影响.

主要方法:

  • 不对称的安萨-金属复合物的合成和应用 (Me(2) Y(Ind) CpMMe(2)).
  • 在不同的单体度下进行的烯聚合实验.
  • 聚合物微观结构的分析,包括战术性和五度分布.
  • 动力建模以确定基本的催化参数 (例如,传播,反转率).

主要成果:

  • 来自Me(2)Si(Ind)CpZrMe(2) 的催化剂在快速链逆转条件下运行,PP微观结构基本上独立于对应物.
  • 聚烯的战术性对具有特定催化剂/联合启动剂组合的单体度敏感 (Me(2) C(Ind) CpHfMe(2) / PMAO或 [Ph(3) C][B(C(6) F(5)) ((4)).
  • 用B(C(6) 激活的催化剂产生了立体规律的PP,其微观结构不变于单体度,表明了一致的操作模式.

结论:

  • 催化剂性能的主要差异来自于操作模式 (相对插入率与反转率),而不是内在的立体选择性.
  • 根据运行制度观察到的对象的排序与基于协调能力的预期有所不同.
  • 这项研究提供了通过催化剂设计和金属催化聚合物的反应条件对聚合物微结构的细微控制的见解.