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Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions
Published on: October 10, 2016
Una investigación mecanicista sobre la copolimerización del etileno con monómeros polares utilizando un catalizador
1Department of Chemistry, University of California, 1102 Natural Sciences 2, Irvine, California 92697, USA.
Journal of the American Chemical Society
|August 12, 2009
Resumen
Este estudio revela que un catalizador de paladio con un ligando ciclófano permite una alta incorporación de etileno y acrilato de metilo (MA) en copolímeros. Esto ocurre porque el ligando impide el intercambio de monómeros, a diferencia de los catalizadores estándar.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Catálisis de polimerización por catálisis de polimerización.
- Estudios Mecanicistas Estudios Mecanicistas
Sus antecedentes:
- Trabajos anteriores mostraron una alta incorporación de acrilato con los catalizadores de ciclófano Pd (II).
- Los catalizadores estándar de Pd(II) alfa-diimina exhiben una cinética de Curtin-Hammett normal en la copolimización.
Objetivo del estudio:
- Para llevar a cabo una investigación mecanicista detallada de la copolimización de acrilato de etileno/metilo (MA) utilizando un catalizador de alfa-diimina basado en Pd(II) ciclófano.
- Para comprender las razones de la incorporación inusualmente alta de MA observada anteriormente.
Principales métodos:
- Investigada la cinética de la copolimización de etileno/MA.
- Se estudiaron las tasas de intercambio de olefinas utilizando espectroscopia 2D EXSY NMR y 1H NMR.
- Determinadas constantes de equilibrio y barreras de activación para el intercambio de olefinas.
Principales resultados:
- El efecto de bloqueo axial del ligando ciclófano impide la sustitución y el equilibrio de las olefinas.
- Las tasas de cambio de etileno fueron más de 100 veces más lentas con el catalizador ciclófano en comparación con los catalizadores acíclicos.
- Se observaron altas barreras de activación para el intercambio de olefinas, comparables a las barreras de inserción migratoria.
Conclusiones:
- El lento intercambio de olefinas debido al ligando ciclófano evita el pre-equilibrio.
- Esto conduce a una reducción de la selectividad del monómero y una alta incorporación del comonomero en la copolimización de etileno/MA.
- El diseño del catalizador ofrece una nueva estrategia para controlar la composición del copolímero.
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