INVESTIGATION OF THE MICROSTRUCTURE OF METALLOCENE-CATALYZED NORBORNENE-ETHYLENE COPOLYMERS USING NMR-SPECTROSCOPY

Norbornene-ethylene copolymers were prepared using the metallocene cat alyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with H-1-NMR and C-13-NMR methods. Fr om a Cosy H-1-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbo rnene units was investigated using C-13-H-1 correlations, hmqc for one -bond correlations, and hmbc for two- or three-bond correlations. It w as shown that norbornene diads were formed at a high norbornene conten t (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy H-1-NMR spectrum revealed a new crosspeak which, according to the corresponding C-13-N MR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norborne ne 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 norborne ne triad is proposed. (C) 1998 John Wiley & Sons, Inc.