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相关概念视频

Polymer Classification: Architecture01:14

Polymer Classification: Architecture

3.7K
Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
3.7K
Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

2.7K
Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
2.7K
Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

4.6K
For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
4.6K
Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

3.7K
Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
3.7K
Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

9.3K
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.
9.3K
Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

3.1K
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...
3.1K

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相关实验视频

Updated: Jan 9, 2026

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction
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Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

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从已知的动态键分布中调整高密度聚乙烯微结构和属性

Christopher B Cooper1, McKenzie L Coughlin1, Polette J Centellas1

  • 1Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.

Journal of the American Chemical Society
|December 4, 2025
PubMed
概括

研究人员使用尿键开发了动态高密度聚乙烯 (HDPE). 这项创新提高了机械性能,为聚烯塑料回收提供了新的途径,聚烯塑料是主要的废物来源.

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Manufacturing of Three-dimensionally Microstructured Nanocomposites through Microfluidic Infiltration
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Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties
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Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

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Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction
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科学领域:

  • 聚合物科学
  • 材料化学
  • 可持续的塑料

背景情况:

  • 包括高密度聚乙烯 (HDPE) 在内的多聚烯占塑料废物的50%以上.
  • 目前的回收方法往往会降低对聚烯特性至关重要的分子质量分布.
  • 保持分子特性是维护可加工性和回收塑料机械强度的关键.

研究的目的:

  • 研究将尿基动态键融入HDPE.
  • 提高HDPE的机械性能,同时保持其理想的特性.
  • 探索半晶体聚合物硬化和设计先进的回收工艺的新策略.

主要方法:

  • 合成了基于尿的动态聚合物.
  • 聚合物的特征包括结晶性,化温度和层状/形态厚度.
  • 使用聚合物物理理论来预测基于键对键间距的材料性质.

主要成果:

  • 动态键通过超分子相互作用加强无形相,绕过对高分子质量链的依赖.
  • 发现关键性质取决于聚合物骨干上的键与键间距的分布.
  • 一种混合骨动态HDPE聚合物表现出优异的机械性能,接近超高分子量聚乙烯的行为.
  • 观测到远程超分子秩序,即使在化状态下也保持稳定.

结论:

  • 动态键的位置显著影响半晶体聚合物的质量特性.
  • 这种方法为固聚合物和设计化学回收方法提供了框架.
  • 控制键间隔分布是开发先进的聚合物材料和回收策略的关键因素.