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Videos de Conceptos Relacionados

Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

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...
Ziegler–Natta Chain-Growth Polymerization: Overview01:17

Ziegler–Natta Chain-Growth Polymerization: Overview

Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta catalyst, high molecular...
Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

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 acceptor.
Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

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...
Anionic Chain-Growth Polymerization: Overview01:20

Anionic Chain-Growth Polymerization: Overview

The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
Polymer Classification: Stereospecificity01:26

Polymer Classification: Stereospecificity

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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Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
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Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

Published on: January 26, 2016

Dinámica vidriosa en cadenas de polímeros aislados condensados.

Martin Tress1, Emmanuel U Mapesa, Wilhelm Kossack

  • 1Faculty of Physics and Earth Science, University of Leipzig, 04103 Leipzig, Germany.

Science (New York, N.Y.)
|September 21, 2013
PubMed
Resumen

Los investigadores estudiaron la dinámica de la cadena de polímeros utilizando condensadores nanoestructurados. Descubrieron que las propiedades de los materiales permanecen en gran medida a granel, incluso a nanoescala, con cambios mínimos cerca de las superficies.

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Área de la Ciencia:

  • Ciencia de los materiales Ciencia de los materiales.
  • Física de los polímeros Física de los polímeros Física de los polímeros Física de los polímeros Física de los polímeros
  • Nanotecnología La nanotecnología es la nanotecnología.

Sus antecedentes:

  • La miniaturización de materiales a la escala nanométrica plantea preguntas sobre cómo cambian las propiedades de los materiales.
  • Comprender la dinámica de las cadenas de polímeros aislados es crucial para las aplicaciones de materiales a nanoescala.

Objetivo del estudio:

  • Para investigar la dinámica de las cadenas de polímeros aislados condensados a nanoescala.
  • Para determinar cómo las propiedades de los materiales se ven afectadas por el confinamiento en entornos nanoestructurados.

Principales métodos:

  • Se utiliza la espectroscopia dieléctrica de banda ancha.
  • Empleó un condensador con electrodos nanoestructurados separados por 35 nanómetros.
  • Se midió la transición dinámica al vidrio de la poli-2-vinilpiridina).

Principales resultados:

  • Se encontró que la transición dinámica de vidrio de la poli (la 2-vinilpiridina) es predominantemente a granel.
  • Sólo los segmentos de polímero dentro de 0,5 nanómetros del sustrato mostraron una ligera desaceleración de la dinámica.
  • Demostró un método para estudiar la dinámica molecular aislada.

Conclusiones:

  • Las propiedades materiales de las cadenas de polímeros se mantienen en gran medida consistentes con el comportamiento a granel, incluso a nanoescala.
  • Las interacciones superficiales tienen un efecto limitado y localizado en la dinámica de la cadena de polímeros.
  • El enfoque desarrollado permite una mayor investigación sobre la dinámica de las moléculas individuales.