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相关概念视频

Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

7.8K
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.
7.8K
Radical Chain-Growth Polymerization: Mechanism01:09

Radical Chain-Growth Polymerization: Mechanism

2.5K
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...
2.5K
Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

2.3K
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...
2.3K
Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

2.0K
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...
2.0K
Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)00:53

Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)

1.9K
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...
1.9K
Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

2.4K
Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...
2.4K

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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
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聚乙烯的机械化学解聚合过程中的动态现象

Yuchen Chang1, Sylvie J Blanton1, Ralph Andraos1

  • 1School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.

ACS sustainable chemistry & engineering
|January 12, 2024
PubMed
概括

在球磨机反应堆中,塑料如聚乙烯的机械化学脱聚合会产生 styrene 单体. 持续去除 styrene 是有效回收的关键,铁表面和氧气增强了这个过程.

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科学领域:

  • 聚合物化学 聚合物化学
  • 材料科学 材料科学 材料科学
  • 化学工程是化学工程的重要组成部分.

背景情况:

  • 合成的多烯塑料占全球塑料垃圾的很大一部分.
  • 通过脱聚合回收化学品是废物管理的一个关键策略.
  • 在环境条件下固态脱聚合提供了一个有前途的回收方法.

研究的目的:

  • 研究聚烯机械化学脱聚合过程中的动力现象.
  • 了解影响 styrene 生产和副产品形成的机制和因素.
  • 评估连续单体去除和促进剂的作用.

主要方法:

  • 在球磨机反应堆中,聚乙烯的固态脱聚合.
  • 分析反应动力学,产品选择性和分子量变化.
  • 研究铁表面和分子氧的影响.

主要成果:

  • 烯单体以恒定的速率和选择性产生.
  • 机制类似于热和氧化热解.
  • 持续的单体去除对于防止重聚合是至关重要的.
  • 铁表面和分子氧气促进了脱聚合过程.
  • 在脱聚合和分子量减少之间观察到的动力独立性.

结论:

  • 机械化学去聚合是一种有效的聚乙烯回收方法.
  • 了解多尺度现象对于优化研磨参数和反应剂成分至关重要.
  • 这种方法有助于可持续的塑料废物管理策略.