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

Abstract

Norbornene–ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with 1H‐NMR and 13C‐NMR methods. From a Cosy 1H‐NMR spectrum it was found that all norbornene units are enchained in the exo‐configuration. The sequence distribution of norbornene units was investigated using 13C‐1H 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 1H‐NMR spectrum revealed a new crosspeak which, according to the corresponding 13C‐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. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1633–1638, 1998

Density Functional Study of Ethylene−Norbornene Copolymerization via Metallocene and Constrained-Geometry Catalysts

“…Therefore, an entropic loss upon complex formation is more dramatic with norbornene than with ethylene. The calculated temperature dependence of the monomer reactivity ratio is also consistent with experimental observations of an increase in the norbornene content with decreasing copolymeriztion temperature 4a…”

Ethylene−Norbornene Copolymer Microstructure. Assessment and Advances Based on Assignments of 13C NMR Spectra

“…These assignments could be easily obtained by analyzing the complete spectra of copolymers with different norbornene content and by comparing the relative peak areas. Several of these assignments are in agreement with those reported by other authors. ,,, A specific comparison of controversial assignments will be presented in one of the following sections.…”

High norbornene incorporation in ethylene-norbornene copolymerization with a bis(α-alkyloxoimine) titanium-MAO catalyst

“…These properties can be precisely controlled by varying monomer composition, sequence distribution, and the stereoregularity of norbornene units in the copolymers, which depends on the different structure of the employed catalyst including metal center and ligand structure. Since Kaminsky initially reported homogeneous metallocene/methylaluminoxane (MAO) for the copolymerization of ethylene and norbornene [7][8][9], more attention has been concentrated on group 4 titanium and zirconium catalysts [10][11][12][13][14][15].…”