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Un "catalizador de geometría restringida" estéricamente expandido para la polimerización y copolimización de olefinas
Levi J Irwin1, Joseph H Reibenspies, Stephen A Miller
1Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, USA.
Journal of the American Chemical Society
|December 23, 2004
Resumen
Un nuevo catalizador de geometría constreñida con una porción de octametiloctahidrodibenzofluoreno exhibe una alta reactividad hacia las alfa-olefinas. Este catalizador, cuando se activa con metilaluminoxano (MAO), muestra una actividad proporcional a la concentración de comonomeros en las copolimieraciones de etileno.
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:
- Los catalizadores de geometría restringida (CGC) son cruciales en la polimerización de las olefinas.
- La masa estéril alrededor del centro del metal influye en la actividad del catalizador y en las propiedades del polímero.
- La incorporación de ligandos voluminosos puede mejorar el rendimiento del catalizador.
Objetivo del estudio:
- Para sintetizar y caracterizar un CGC estérico expandido que incorpora una fracción de 14A octametilotahidrodibenzofluoreno.
- Evaluar la actividad catalítica del nuevo catalizador (1) en la polimerización de las olefinas, particularmente hacia las alfa-olefinas.
- Para investigar el comportamiento de copolimización del catalizador con etileno y alfa-olefinas superiores.
Principales métodos:
- Síntesis del catalizador de geometría constreñida Me2Si(eta1-C29H36) ((eta1-N-tBu) ZrCl2.OEt2 (1).
- Análisis estructural en estado sólido del catalizador.
- Experimentos de polimerización y copolimización de olefinas utilizando el catalizador activado con metilaluminoxano (MAO).
- Análisis cinético de las actividades de polimerización.
Principales resultados:
- La estructura en estado sólido del catalizador (1) indica una significativa accesibilidad espacial.
- El catalizador (1) / MAO demuestra una reactividad extraordinaria hacia las alfa-olefinas, que excede la reactividad hacia el etileno.
- Las actividades en la copolimización con etileno son linealmente y continuamente proporcionales a la concentración de 4-metil-1-penteno o 1-octeno.
Conclusiones:
- El diseño de ligando estérico expandido mejora la accesibilidad y la reactividad del catalizador.
- El catalizador exhibe una reactividad selectiva hacia las alfa-olefinas más altas sobre el etileno.
- La relación lineal observada entre la actividad y la concentración del comonomero proporciona información sobre la cinética de la copolimización.
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