Investigation of the microstructure of metallocene-catalyzed norbornene–ethylene copolymers using NMR spectroscopy

✍ Scribed by Christer H. Bergström; Bernd R. Sperlich; Juhana Ruotoistenmäki; Jukka V. Seppälä

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 196 KB
• Volume: 36
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(19980730)36:10<1633::aid-pola16>3.0.co;2-h

✦ Synopsis

Norbornene-ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with 1 H-NMR and 13 C-NMR methods. From a Cosy 1 H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using 13 C-1 H correlations, hmqc for one-bond correlations, and hmbc for two-or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy 1 H-NMR spectrum revealed a new crosspeak which, according to the corresponding 13 C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed.