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

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

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...
Olefin Metathesis Polymerization: Overview01:13

Olefin Metathesis Polymerization: Overview

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.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

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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Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
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Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

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All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...

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Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes
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Control de redox de un catalizador de polimerización de apertura de anillo

Erin M Broderick1, Neng Guo, Carola S Vogel

  • 1Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095, USA.

Journal of the American Chemical Society
|May 25, 2011
PubMed
Resumen
Este resumen es generado por máquina.

El control redox de los complejos de alcóxido de yttrio e indio modula las tasas de polimerización. Esta actividad dependiente de los metales ofrece nuevas estrategias para la síntesis de polímeros, en particular para el L-lactido y el carbonato de trimetileno.

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Área de la Ciencia:

  • Química organometálica Química orgánica de los metales.
  • La ciencia de los polímeros es la ciencia de los polímeros.
  • La catálisis de la catálisis.

Sus antecedentes:

  • La polimerización de apertura de anillos (ROP) es crucial para la síntesis de polímeros biodegradables.
  • El control de la actividad del catalizador a través de estímulos externos como los cambios redox es un área activa de investigación.
  • Los ligandos basados en ferroceno ofrecen propiedades redox únicas para los complejos metálicos.

Objetivo del estudio:

  • Para investigar el control redox de los complejos de alcóxido de yttrio e indio en ROP.
  • Para explorar la influencia de la identidad del metal en el comportamiento de polimerización.
  • Para sintetizar y caracterizar polímeros derivados de L-lactida y carbonato de trimetileno.

Principales métodos:

  • Síntesis y caracterización del complejo de alcóxido de ittrio con un ligando de ferroceno.
  • Manipulación de redox del complejo de ittrio utilizando reactivos químicos.
  • Cristalografía de rayos X, RMN, XANES y espectroscopia de Mössbauer para la caracterización.
  • La polimerización de apertura de anillos de L-lactido y carbonato de trimetileno.
  • Cromatografía por permeación de gel para el análisis de polímeros.

Principales resultados:

  • La tasa de polimerización del complejo de itrio fue modulada por cambios en el estado redox.
  • Las formas oxidadas y reducidas del complejo de yttrium exhibieron diferentes actividades catalíticas.
  • El complejo de alcóxido de indio mostró un comportamiento inverso en comparación con el ítrio.
  • Se observó una clara dependencia de la tasa de polimerización basada en el metal.

Conclusiones:

  • Los complejos de alcóxido de yttrio e indio con conmutación redox pueden controlar las tasas de polimerización.
  • El comportamiento dependiente del metal observado pone de relieve la importancia del centro metálico en la actividad catalítica.
  • Este estudio proporciona información sobre el diseño de catalizadores con respuesta redox para la síntesis controlada de polímeros.