Ch. Bergstrom et al., INVESTIGATION OF THE MICROSTRUCTURE OF METALLOCENE-CATALYZED NORBORNENE-ETHYLENE COPOLYMERS USING NMR-SPECTROSCOPY, Journal of polymer science. Part A, Polymer chemistry, 36(10), 1998, pp. 1633-1638
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.