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相关概念视频

Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

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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...
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Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

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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...
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Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

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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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Step-Growth Polymerization: Overview01:03

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Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
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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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Olefin Metathesis Polymerization: Overview01:13

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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.
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在化处理的分子半导体晶体中进行聚合物辅助的多态转换.

Pallavi Sundaram1, Rochelle B Spencer1, Akash Tiwari1

  • 1Molecular Design Institute, Department of Chemistry, New York University, New York, New York 10003, United States.

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PubMed
概括

在与聚乙烯 (PE) 的混合物中出现了一种新的多态 (II 形式) 5,11-bis ((triisopropylsilylethynyl) anhradithiophene (TIPS ADT). 这一发现影响了有机半导体的结晶和性能.

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科学领域:

  • 材料科学 材料科学 材料科学
  • 晶体学 晶体学是指结晶学.
  • 有机电子 有机电子

背景情况:

  • 有机半导体如5,11-bis ((triisopropylsilylethynyl) anhradithiophene (TIPS ADT) 呈现多态性,影响其电子特性.
  • 化处理为制造有机电子设备提供了溶液加工的替代方案,但可以导致不同的晶体结构.
  • 聚合物混合物在炼过程中对有机半导体结晶行为的影响尚未完全理解.

研究的目的:

  • 通过化处理,研究TIPS ADT在与中密度聚乙烯 (PE) 的混合物中的结晶.
  • 为了识别和描述在这些条件下形成的TIPS ADT的新多态.
  • 了解PE在TIPS ADT的阶段过渡和晶体增长中的作用.

主要方法:

  • TIPS ADT的炼加工与16 ± 1重量%的PE混合.
  • 从融中结晶,然后在100°C冷却和热.
  • 使用对晶体结构和形态 (隐含) 敏感的技术对晶体相的表征.

主要成果:

  • 一种TIPS ADT的新型多态,被指定为Form II,从化处理的TIPS ADT/PE混合物中结晶.
  • 化处理的TIPS ADT/PE最初形成了一个具有工包装图案的转移稳定多态 (Form IV).
  • 化诱导了从形式IV到形式II的过渡,形式II的增长受到初始球状岩结构的影响;这种过渡在整洁的TIPS ADT片中缺席.

结论:

  • 中密度聚乙烯 (PE) 在化处理和随后的化过程中促进了新的TIPS ADT多态 (形式II) 的形成.
  • 移动PE阶段提高了TIPS ADT扩散和核化速率,促进了IV → II形式的过渡.
  • 与变态稳定的IV型晶体相比,II型晶体表现出不同的电子性质 (传导性较低,排放性较低).