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Related Concept Videos

Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

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The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
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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...
2.0K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.2K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
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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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Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

2.0K
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...
2.0K
Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

2.1K
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...
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Updated: Sep 30, 2025

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

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Visualization of on-surface ethylene polymerization through ethylene insertion.

Weijun Guo1,2, Junqing Yin3, Zhen Xu2

  • 1SynCat@Beijing, Synfuels China Technology Co., Ltd., Beijing 101407, China.

Science (New York, N.Y.)
|March 10, 2022
PubMed
Summary

This study visualizes ethylene polymerization using scanning tunneling microscopy. It reveals a self-initiation mechanism on iron carbide surfaces, confirming the ethylene insertion pathway at the molecular level.

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Area of Science:

  • Catalysis
  • Polymer Chemistry
  • Surface Science

Background:

  • Catalytic ethylene polymerization is a cornerstone of the chemical industry, producing polyethylene.
  • The widely accepted Cossee-Arlman mechanism describes chain growth via ethylene insertion into metal-carbon bonds.
  • Experimental, molecular-level confirmation of this mechanism has been lacking.

Purpose of the Study:

  • To provide direct, microscopic, and spatiotemporal experimental evidence for the ethylene polymerization mechanism.
  • To visualize the process of ethylene polymerization at the molecular level.
  • To elucidate the initiation and propagation steps in ethylene polymerization on a specific catalytic surface.

Main Methods:

  • In situ visualization of ethylene polymerization using scanning tunneling microscopy (STM).
  • Utilizing a carburized iron single-crystal surface as the catalyst.
  • Observation of polymerization intermediates and chain growth dynamics.

Main Results:

  • Ethylene polymerization was observed to occur on specific triangular iron sites at the boundary of carbide domains.
  • A novel self-initiation pathway was identified, involving a surface-anchored ethylidene intermediate.
  • Subsequent ethylene insertion into this intermediate was visualized, confirming chain growth.

Conclusions:

  • Direct experimental evidence confirms the ethylene polymerization pathway at the molecular level.
  • The findings validate and refine the understanding of the Cossee-Arlman mechanism.
  • The study highlights the role of specific surface sites and intermediates in catalytic polymerization.