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Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

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The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
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Polymer Classification: Architecture01:14

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Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
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Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

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The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
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Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)00:53

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Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
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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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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.
Many natural and synthetic polymers are produced by...
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Los oligómeros de etileno hiperbranqueados monofuncionales son oligómeros de etileno hiperbranqueados.

Thomas Wiedemann1, Gregor Voit, Alexandra Tchernook

  • 1Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz , 78464 Konstanz, Germany.

Journal of the American Chemical Society
|January 24, 2014
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Resumen

Los catalizadores de níquel convierten el etileno en oligómeros hiperbranqueados. Los sustituyentes de catalizadores controlan la ramificación y el peso molecular, con un catalizador que muestra una amplia aplicabilidad. La funcionalización con ésteres, alcoholes o epóxidos es eficiente y escalable.

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Área de la Ciencia:

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

Sus antecedentes:

  • El desarrollo de catalizadores eficientes para la oligomerización del etileno es crucial para la producción de materiales de valor agregado.
  • Los polímeros hiperbranqueados ofrecen propiedades únicas debido a su estructura globular y alta densidad de grupos funcionales.
  • El control de la arquitectura del polímero y la habilitación de la funcionalidad selectiva son desafíos clave en la síntesis de polímeros.

Objetivo del estudio:

  • Para sintetizar y evaluar los complejos neutros κ(2) N,O-salicylaldiminato Ni(II) como catalizadores para la oligomerización del etileno.
  • Investigar la influencia de la estructura del catalizador en las propiedades de los oligómeros hiperbranqueados, incluyendo la densidad de ramificación y el peso molecular.
  • Desarrollar métodos escalables para la monofuncionalización selectiva de los oligómeros hiperbranqueados resultantes.

Principales métodos:

  • Síntesis de complejos de níquel (II) salicilaldiminato con diferentes sustituyentes remotos (R = Me, Et, iPr).
  • Reacciones de oligomerización de etileno bajo diferentes presiones y temperaturas utilizando los catalizadores sintetizados.
  • Preparación y evaluación del sistema de catalizador in situ.
  • Funcionalización posterior a la oligomerización a través de la etoxicarbonilación, la metatesis cruzada con acrilato de etilo seguida de la hidrogenación y la epoxidación.

Principales resultados:

  • Todos los catalizadores produjeron oligoetilenos hiperbranqueados de bajo peso molecular (Mn ≈ 1000 g mol-1) con alta productividad.
  • La densidad de ramificación disminuyó y el peso molecular aumentó con sustitutos más voluminosos (Me > Et > iPr).
  • El catalizador 1a-pyr (R=Me) demostró un rendimiento robusto en una amplia gama de condiciones de reacción.
  • Un sistema in situ coincidía con la actividad y la microestructura de los catalizadores preformados.
  • La introducción selectiva de grupos funcionales de éster, alcohol y epóxido se logró de manera eficiente y escalable.

Conclusiones:

  • Los complejos neutrales de salicilaldiminato Ni (II) son catalizadores efectivos para la producción de oligoetileno hiperbranqueado.
  • El diseño del catalizador permite ajustar la arquitectura y las propiedades del polímero.
  • Los métodos escalables y eficientes para la monofuncionalización abren vías para la creación de nuevos materiales funcionales.