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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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Anionic Chain-Growth Polymerization: Mechanism01:04

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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...
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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: Ring-Opening Metathesis Polymerization (ROMP)01:16

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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
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Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶  nucleation, elongation, and steady-state phase.
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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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Un mecanismo dinuclear implicado en la polimerización controlada de carbenos

Aleksandr V Zhukhovitskiy1, Ilia J Kobylianskii1, Andy A Thomas2

  • 1Department of Chemistry , University of California , Berkeley , California 94720 , United States.

Journal of the American Chemical Society
|April 10, 2019
PubMed
Resumen

Los investigadores desarrollaron nuevos iniciadores de paladio para la polimerización controlada de carbenos. Este avance permite la síntesis de poliolefinas avanzadas con propiedades sintonizables y estructuras bien definidas.

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Área de la Ciencia:

  • Química de los polímeros
  • Química organometálica
  • Ciencias de los materiales

Sus antecedentes:

  • La polimerización de carbenos ofrece una ruta a poliolefinas únicas que no son accesibles a través de la polimerización tradicional de olefinas.
  • Lograr la polimerización de carbenos controlada y viva ha seguido siendo un desafío significativo en la ciencia de los polímeros.

Objetivo del estudio:

  • Desarrollar nuevos iniciadores para la polimerización controlada y cuasi viva de carbenos.
  • Para sintetizar poliolefinas con altos pesos moleculares, dispersiones estrechas y extremos de cadena definidos.
  • Investigar el mecanismo de este nuevo proceso de polimerización.

Principales métodos:

  • Utilizó dimeros de carboxilato de paladio (π-alilo) como iniciadores.
  • El diazoacetato de etilo polimerizado, un precursor del carbeno.
  • Se ha empleado el análisis mecanicista experimental y teórico.
  • Copolicarbenos de bloque sintetizados.

Principales resultados:

  • Se ha logrado una polimerización de carbenos controlada y casi viva con rendimientos casi cuantitativos.
  • Polímeros producidos con grados de polimerización superiores a 100 y dispersiones de peso molecular de 1,2-1,4.
  • Polímeros generados con extremos de cadena bien definidos y diversificables.
  • Se han sintetizado con éxito copolicarbenos de bloque que muestran segregación de microfase.
  • Elucidado un nuevo mecanismo dinuclear para el proceso de polimerización.

Conclusiones:

  • Se introdujo una nueva clase de iniciadores de paladio para la polimerización controlada de carbenos.
  • Demostró la capacidad de sintetizar poliolefinas bien definidas y bloquear copolímeros.
  • Proporcionó conocimientos mecanicistas sobre una nueva vía de polimerización dinuclear.