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相关概念视频

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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...
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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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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...
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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...
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带有基团的线性聚乙烯可光降解性:侧链碳基的效率高于内链碳基

Haobo Yuan1, Kohei Takahashi1, Shintaro Nakagawa2

  • 1Graduate School of Engineering, The University of Tokyo, Tokyo, 113-8656, Japan.

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带有侧链基团的聚乙烯 (poly(E/MVK)) 比带有链内碳基团的聚乙烯 (poly(E/CO)) 更快地降解. 这种增强的光降解是由于聚E/MVK的诺里什型I和II裂变.

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科学领域:

  • 聚合物化学
  • 材料科学
  • 光降解研究

背景情况:

  • 聚乙烯是一种易于光降解的广泛使用的塑料.
  • 引入碳基可以改变聚乙烯的降解途径.
  • 了解降解机制对于材料设计和回收至关重要.

研究的目的:

  • 为了比较线性聚乙烯与侧链基 (poly ((E/MVK)) 与链内碳基 (poly ((E/CO)) 的光降解行为.
  • 通过光谱分析阐明聚E/MVK的降解机制.
  • 研究高密度聚乙烯 (HDPE) 的混合物中的聚乙烯 (E/MVK) 的代谢.

主要方法:

  • 乙烯和甲基乙烯基的催化共聚化合成聚E/MVK.
  • 照相降解实验比较聚E/MVK和聚E/CO.
  • 核磁共振 (NMR) 光谱分析降解产物和机制.

主要成果:

  • 与聚乙相比,聚乙 (E/MVK) 的光降解速度明显更快.
  • 在光降解过程中,聚乙烯 (E/ MVK) 的分子量下降更明显.
  • H 核磁共振分析表明,诺里什 I 型和 II 型裂变都会导致聚E/MVK 的降解.
  • 甲基乙基 (MVK) 组在聚E/MVK的无形区域中存在,可能会促进基链反应和主链裂变.

结论:

  • 具有侧链基团的线性聚乙烯显示加速光降解.
  • 聚E/MVK的降解机制涉及诺里什型I和II反应,通过侧链MVK组的可访问性得到增强.
  • 聚E/MVK) 具有可控降解应用的潜力,并且可以影响混合HDPE的降解.