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Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

2.7K
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...
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Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

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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...
2.4K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.1K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
2.1K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.9K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Structure of Conjugated Dienes01:16

Structure of Conjugated Dienes

6.6K
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
6.6K
Anionic Chain-Growth Polymerization: Overview01:20

Anionic Chain-Growth Polymerization: Overview

2.5K
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,...
2.5K

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Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering
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在序列定义的结合寡合体中进行电荷传输

Hao Yu1, Songsong Li2,3, Kenneth E Schwieter4

  • 1Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.

Journal of the American Chemical Society
|February 19, 2020
PubMed
概括

合成聚合物中的单体序列显著影响电荷传输. 结合的寡合体中的特定序列通过创建独特的电荷通路来增强分子导电性超过10倍.

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科学领域:

  • 聚合物化学
  • 材料科学
  • 分子电子

背景情况:

  • 对于合成聚合物来说,了解单体序列和材料特性之间的关系至关重要.
  • 结合性寡聚体中的电荷传输是分子电子学的关键因素.

研究的目的:

  • 研究主要单体序列如何影响单分子结合中的电荷传输.
  • 合成和表征序列定义的结合寡合体.

主要方法:

  • 使用范·莱森反应进行代合成,以产生序列定义的寡合物 (2-7个单位).
  • 使用扫描道显微镜断裂结 (STM-BJ) 技术对电荷传输特性进行表征.
  • 测量各种寡合体长度的分子导电性.

主要成果:

  • 发现特定的单体序列可将分子导电率提高10倍以上.
  • 序列定义的胺与伊米达或醇组促进了多重导电通路.
  • 固体阻碍和异环方向性在电荷运输中起着至关重要的作用.

结论:

  • 单体序列是控制合寡合体中的电荷传输的关键设计参数.
  • 定制分子结构可以提高分子电子设备的性能.
  • 这项研究为设计先进的分子电子元件提供了见解.