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Homopolimerizaciones y copolimerizaciones estereoselectivas coordinativas/insertivas mediadas por organotitanio de
Tryg R Jensen1, Sung Cheol Yoon, Aswini K Dash
1Chemistry Department, Northwestern University, Evanston, IL 60208-3113, USA.
Journal of the American Chemical Society
|November 20, 2003
Resumen
Un nuevo catalizador de organotitanio permite la polimerización estereorregular de estireno y metacrilato de metilo (MMA). Este catalizador produce poliestireno sindiotáctico (s-PS) y metacrilato polimetilo (s-PMMA), y copolymeriza de manera única el MMA y el estireno.
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:
- La polimerización estereorregular de las olefinas es crucial para adaptar las propiedades de los polímeros.
- El desarrollo de catalizadores de un solo sitio para la polimerización controlada de diversos monómeros sigue siendo un desafío.
- Comprender los mecanismos de copolimerización es clave para diseñar materiales avanzados.
Objetivo del estudio:
- Investigar el comportamiento de polimerización y copolimerización del estireno y el metacrilato de metilo (MMA) utilizando un nuevo catalizador de organotitanio.
- Para aclarar el mecanismo de la homopolimerización estereorregular y la copolimización mediada por este catalizador de un solo sitio.
- Explorar el potencial de este sistema catalizador para la creación de nuevos copolímeros con microestructuras controladas.
Principales métodos:
- Preparación de un catalizador de organotitanio de un solo sitio altamente activo a través de la reducción in situ de Zn.
- Homopolimerización de estireno y MMA utilizando el catalizador desarrollado.
- Copolimización de estireno y MMA en diversas condiciones, seguido de experimentos de control mecánico.
Principales resultados:
- El catalizador produjo de manera eficiente el poliestireno sindiotáctico (s-PS, >95% de sindiotáctica, 170.000 g/mol) a través de una vía coordinativa/insertiva.
- El mismo catalizador produjo poli (methacrilato de metilo) sindiotáctico (s-PMMA, >65% de sindiotáctica, >70.000 g/mol) a través de un mecanismo similar al GTP.
- La copolimerización del estireno y el MMA (proporción 1:19) a 50°C dio como resultado al azar, aproximadamente un 80% de poli[estireno-co-metilacrilato] (coiso-PSMMA) coisotactico aleatorio que contiene ~4% de MMA, lo que sugiere un nuevo mecanismo de adición conjugada.
Conclusiones:
- Un catalizador de un solo sitio de organotitanio media efectivamente la homopolimerización estereorregular de estireno y MMA.
- El catalizador demuestra una capacidad única para copolimerizar estireno y MMA, desafiando los mecanismos de no coordinación existentes.
- Se propone un nuevo mecanismo que implica pasos secuenciales de adición conjugada para explicar el comportamiento de copolimización observado.
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