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Mecanismos de control estereoquímico en la polimerización del propileno mediada por centros catalizadores de titanio
Alessandro Motta1, Ignazio L Fragalà, Tobin J Marks
1Dipartimento di Scienze Chimiche, Università di Catania, and INSTM, UdR Catania, Viale A. Doria 6, 95125 Catania, Italy.
Journal of the American Chemical Society
|May 22, 2007
Resumen
Este estudio sobre la polimerización de las olefinas revela que, si bien las contraiones afectan la actividad del catalizador, no alteran significativamente la estereocímica del polímero. Los modelos computacionales simplifican el análisis, mostrando que los factores estéricos dominan la encadenamiento de monómeros para la formación de polímeros isotácticos.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- La ciencia de los polímeros es la ciencia de los polímeros.
- Química computacional es la química computacional.
Sus antecedentes:
- Los catalizadores de geometría restringida (CGC) son vitales en la polimerización de las olefinas.
- Comprender el control estereoquímico en la polimerización es crucial para adaptar las propiedades del polímero.
Objetivo del estudio:
- Para analizar los aspectos estereoquímicos de la polimerización de olefinas utilizando un catalizador de geometría constreñida simétrico C1.
- Para investigar la influencia del cocatalizador / contraanión y la solvación en la activación del catalizador y la inserción del monómero.
Principales métodos:
- Los cálculos de la Teoría Funcional de Densidad (DFT) se emplearon para estudiar la activación del catalizador y las energías de separación de pares de iones.
- Se generaron perfiles termodinámicos computacionales para las reacciones de inserción de etileno y propileno.
- Se evaluaron sistemáticamente los efectos de los conteriones y los entornos de solvación.
Principales resultados:
- Las energías de activación del catalizador se alinean bien con los datos experimentales.
- Las contrapartes influyen en la actividad catalítica general, pero no significativamente en la microtacticidad del polímero o en la estereoquímica de encadenamiento.
- Los efectos estéricos, particularmente de la cadena de polímero en crecimiento, dictan predominantemente la regioselección y favorecen el enriquecimiento isotáctico durante la inserción de monómeros.
Conclusiones:
- El modelo de "catión desnudo" está computacionalmente justificado para analizar la encadenamiento de monómeros.
- Las interacciones estéricas son los principales impulsores del control estereoquímico en este sistema catalítico.
- Los hallazgos proporcionan información sobre el diseño de catalizadores para microestructuras poliméricas específicas.
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