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La polimerización controlada y estereoselectiva del lactido: cinética, selectividad y microestructuras
Zhiyuan Zhong1, Pieter J Dijkstra, Jan Feijen
1Department of Polymer Chemistry and Biomaterials and Institute for Biomedical Technology, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
Journal of the American Chemical Society
|October 14, 2005
Resumen
Los catalizadores de aluminio quiral permiten la polimerización estereoselectiva de apertura de anillos de lactida, produciendo polilactidos con pesos moleculares y microestructuras controlados. Estos catalizadores ofrecen un control preciso de las propiedades del polímero para aplicaciones de materiales avanzados.
Área de la Ciencia:
- Química de Polímeros La Química de Polímeros es la química de los polímeros.
- Química organometálica Química orgánica de los metales.
- Ciencia de los materiales Ciencia de los materiales.
Sus antecedentes:
- La polimerización de apertura de anillos (ROP) es crucial para la síntesis de polímeros biodegradables como el polilactido.
- El control de la microestructura y la estereoquímica del polímero es esencial para adaptar las propiedades de los materiales.
- Los catalizadores quirales ofrecen vías para la polimerización estereoselectiva, pero aún se están desarrollando sistemas eficientes para el lactido.
Objetivo del estudio:
- Para preparar y caracterizar isopropoxidos quirales de aluminio basados en el ligando de ciclohexilsaleno.
- Para investigar la polimerización estereoselectiva de apertura de anillos de lactida utilizando estos catalizadores.
- Para determinar la cinética, la selectividad y las resultantes microestructuras polilactídicas.
Principales métodos:
- Síntesis de isopropoxidos quirales de aluminio con enantiopuro o racemic ligandos ciclohexylsalen.
- La polimerización de apertura de anillos de enantiómeros de lactido y mezclas racémicas en tolueno a 70°C.
- Estudios cinéticos, análisis del peso molecular del polímero, polidispersidad y microestructura (espectroscopia de RMN).
- Determinación de la selectividad del catalizador utilizando relaciones de velocidad constante y factores de selectividad.
Principales resultados:
- Se obtuvieron constantemente polilactidos con peso molecular controlado, baja polidispersidad y grupos finales definidos.
- (R,R) -CyclohexylsalenAlO ((i) ((() Pr polimerizó el l-lactido aproximadamente 14 veces más rápido que el d-lactido.
- La polimerización del rac-lactido con (R,R)-1 produjo polímeros cristalinos con un factor de selectividad de ~5.5.5.
- Los copolilactidos estereobloqueantes con altos puntos de fusión y cristalinidad fueron sintetizados a partir de mezclas de lactida y catalizadores racémicos.
Conclusiones:
- Los isopropoxidos de aluminio quiral son catalizadores efectivos para la polimerización estereoselectiva de lactida.
- Los catalizadores proporcionan el control sobre el peso molecular del polímero, la polidispersidad y la estereoquímica.
- Estos hallazgos permiten la síntesis de polilactidos a medida con microestructuras y propiedades específicas para diversas aplicaciones.
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