SUMMARY: Ethene and norbornene were copolymerized using metallocene catalysts that produce copolymers having isolated norbornene units or microblocks with a maximum of two norbornene units. The resonances of the norbornene C 5/6 and the ethene carbon atoms, which overlap extensively in the 13 C NMR spectrum, were differentiated and assigned by comparing the 13 C NMR spectra of the copolymers obtained from monomers having 13 C at natural abundance with those prepared from feedstocks containing 13 C 1 -enriched ethene or 13 C 5/6 -enriched norbornene. The NMR analysis revealed that the chemical shifts of the norbornene C 5/6 carbon atoms are triad sensitive and those of the ethene carbon atoms are pentad sensitive. 13C NMR analysis of copolymers containing isolated norbornene units in various proportions allowed the resonances of the norbornene C 5/6 and the ethene carbon atoms to be assigned to the respective triads and pentads. The complete triad distributions of these copolymers determined in this way were used to calculate the copolymerization parameters for a representative metallocene catalyst.

Terpolymerizations of norbornene derivatives containing different functional substituents were carried out with ethene and norbornene using the homogeneous catalyst system iPr[CpInd]ZrCl2/MAO. The norbornene derivatives 5‐norbornene‐2‐methanol and 5‐norbornene‐2‐carboxylic acid were prereacted with triisobutylaluminium to prevent the deactivation of the catalyst. 13C NMR studies revealed the composition of the polymer. The incorporation rate was 5–12 mol‐% at a content of 50 mol‐% of the norbornene derivative in the monomer feedstock. IR‐GPC coupled experiments confirmed the homogeneous composition of the polymer. In addition, we investigated the ethene copolymerization and the ethene/norbornene terpolymerization using the trialkylsilyl protected norbornene derivates such as 5‐norbornene‐2‐methyleneoxytriethylsilane and 5‐norbornene‐2‐methyleneoxy‐tert‐butyldimethylsilane. These norbornene derivatives reveal an incorporation rate of 5–6 mol‐% in the polymer at a content of 20 mol‐% in the monomer feedstock.

Summary: The influence of the protecting group of polar norbornene derivatives and the structure of homogenous metallocene/MAO catalyst systems on the activity and the incorporation rates during ethene copolymerization reactions were studied. By varying the structure of the protecting group a relationship between the catalyst activity and the steric demand of the protecting group could be established. For the catalyst systems tested analogous relationships between the bulkiness of the protecting groups and the polymerization activity were found. Kinetic investigations point to a reversible deactivation reaction, during which a bond between the oxygen atom of the polar norbornene derivative and the center of the active catalyst is formed, competing with the olefin coordination and the subsequent insertion. The degree of polymerization deactivation can be qualitatively judged based on a correlation between calculated structural parameters of the trialkylsilyl protected norbornene derivatives and the experimentally determined polymerization activity.image

The 13C NMR spectra of ethene/norbornene copolymers in which there are no norbornene microblocks are much simpler than those of copolymers in which norbornene microblocks are present, making it possible to completely assign all the 13C resonances to the corresponding pentads in the copolymer chain. However, there is disagreement in the literature over several assignments of the ethene 13C NMR signals. In this paper these discrepancies are summarized and discussed. This contribution also reports ethene/norbornene copolymerizations carried out at various temperatures using the homogeneous catalyst system Pri[(3‐Pri‐Cp)Flu]ZrCl2. The 13C NMR spectra of the copolymers were analyzed in the light of the discussion above and the triad distributions were used to determine the copolymerization parameters by Markov first‐ and second‐order statistical models. On the basis of these results, the mechanism generating such an alternating microstructure in these copolymers is discussed and compared with the mechanism previously proposed in the literature. The 13C NMR spectrum with signal assignments of an ethene/norbornene copolymer without norbornene microblocks.magnified imageThe 13C NMR spectrum with signal assignments of an ethene/norbornene copolymer without norbornene microblocks.