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Copolimerización estereospecífica alterna de etileno y propileno con catalizadores de metaloceno
W Fan1, M K Leclerc, R M Waymouth
1Deparmtment of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
Journal of the American Chemical Society
|September 27, 2001
Resumen
Los metalocenos puentes permiten la copolimización alterna de etileno/propileno, dando secuencias específicas. La estructura del metalloceno influye en las propiedades del copolímero, como la actividad y la estereoquímica.
Área de la Ciencia:
- Química de Polímeros La Química de Polímeros es la química de los polímeros.
- Química organometálica Química orgánica de los metales.
Sus antecedentes:
- Los catalizadores de metaloceno son cruciales para la polimerización de las olefinas.
- Comprender la influencia de la estructura del catalizador en la copolimización es clave para controlar las propiedades del polímero.
Objetivo del estudio:
- Para investigar la copolimización de etileno/propileno utilizando metallocenos puenteados.
- Para determinar cómo la estructura del metalloceno (sustituto R, puente E) afecta el comportamiento de copolimización y las características del polímero.
Principales métodos:
- Copolimización de etileno y propileno utilizando varios metallocenos puentes (puentes de carbono y puentes de silicio) con cocatalizador MAO.
- Análisis de la distribución de la secuencia de copolímero (triadas EPE+PEP), el peso molecular y la estereoquímica.
Principales resultados:
- Los metalocenos con sitios activos heterotópicos producen copolímeros alternos de etileno/propileno (61-76% de las tríadas EPE+PEP).
- Los metallocenos con puente de silicio mostraron mayor actividad y peso molecular, pero menor incorporación de propileno en comparación con los puentes de carbono.
- Las secuencias isotácticas PEPEP fueron consistentes en todos los metallocenos; la táctica de la secuencia EPPE varió.
Conclusiones:
- La naturaleza del sustituto (R) y el puente (E) tienen un impacto significativo en la actividad de copolimización, la distribución de la secuencia, el peso molecular y la estereoquímica.
- La copolimización alterna ocurre a través de la inserción secuencial de monómeros en sitios heterotópicos.
- Las secuencias EPPE isotácticas sugieren inserciones múltiples ocasionales debido a la isomerización de la cadena (backskip).
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