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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 species into...
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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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Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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Un polímero con una longitud oculta mecanoquímica activa

Yancong Tian1, Xiaodong Cao2, Xun Li3

  • 1Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.

Journal of the American Chemical Society
|October 16, 2020
PubMed
Resumen
Este resumen es generado por máquina.

Los investigadores desarrollaron nuevas cadenas de polímeros con reactividad mecanoquímica incorporada. Esta innovación mejora significativamente las propiedades mecánicas al permitir el alivio de la tensión sin fractura de la cadena, mejorando la disipación de energía.

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Área de la Ciencia:

  • Química de los polímeros
  • Ciencias de los materiales
  • Mecanoquímica

Sus antecedentes:

  • La incorporación de longitud oculta en las cadenas de polímero mejora las propiedades mecánicas al permitir el alivio de la tensión localizada.
  • Los diseños actuales se centran en los enlaces de sacrificio, pero no en la reactividad mecanoquímica dentro de la longitud oculta en sí.

Objetivo del estudio:

  • Demostrar las ventajas de integrar la reactividad mecanoquímica en la longitud oculta de las cadenas de polímeros.
  • Introducir un nuevo mecanismo para mejorar las propiedades mecánicas del polímero.

Principales métodos:

  • Síntesis de un nuevo mecanóforo que integra el (Z) -2,3-difenilciclobuteno-1,4-dicarboxilato en dimeros macrocíclicos de cinamato.
  • Estiramiento mecánico del polímero y cálculos DFT para analizar la disipación de energía y la mecánica de la fractura.
  • Soluciones sonicadas para el estudio de las reacciones mecanoquímicas y la validación de modelos computacionales.

Principales resultados:

  • El estiramiento del polímero más que duplica su longitud de contorno sin fractura.
  • El nuevo mecanóforo exhibe un aumento de 11 veces en la energía de fractura de la cadena en comparación con los poliéster simples.
  • Se mantiene una alta capacidad de disipación de energía hasta aproximadamente 3 nN.

Conclusiones:

  • La adición de reactividad mecanoquímica a la longitud oculta ofrece ventajas significativas sobre los diseños tradicionales.
  • El mecanóforo desarrollado proporciona propiedades mecánicas superiores y disipación de energía.
  • El estudio valida modelos computacionales y sugiere métodos para cuantificar las fuerzas de una sola cadena.