The kinetics of ethene-norbornene copolymerizations using the metallocenes iPr[(3-R-Cp)Ind]ZrCl2 (with R = methyl or tert-butyl), MeCH[Cp]2ZrCl2, iPr[(3-R-Cp)Flu]ZrCl2 (with R = H, methyl, isopropyl, or tert-butyl), and Me2Si[(3-tert-butyl-Cp)Flu]ZrCl2 and half-sandwich catalysts Me2Si[Me4CpNtBu]TiCl2, Me2Si[Me4CpNtBu]ZrCl2, Me2Si[FluNtBu]ZrCl2, R-(+)-Me2Si[Me4CpNCH(CH3)-1-naphthyl]TiCl2, and C2H4[Me4CpNMe2]Cr(eta1,eta1-C4H8) together with methylaluminoxane as cocatalyst, have been investigated at 70 degreesC in a concentrated solution of norbornene in toluene and under an ethene pressure ranging from 4 to 60 bar (58-870 psi). The ethene reaction rates were measured during the copolymerization process at various ethene concentrations and the ethene reaction orders were determined. In some cases fractional ethene reaction orders higher than 1 were found, indicating a complex mechanism. The microstructure of the copolymers were analyzed by 13C NMR spectroscopy. The highest norbornene contents were achieved using metallocenes with sterically less demanding ligands such as MeCH[Cp]2ZrCl2. Unexpectedly, low norbornene contents (<50 mol %) were achieved with the half-sandwich catalysts. Depending on the catalyst structure, the microstructure of the copolymers consists of mainly isolated norbornene units, alternating monomer sequences or short norbornene microblocks with a maximum length of two or three. Additionally, the tacticity of the norbornene microblocks could be controlled by the catalyst structure. A mechanistic model, based on chain migratory insertion, is presented to explain the different copolymer structures through nonbonding steric interactions between monomer, growing polymer chain, and ligand system. On the basis of this model, penultimate effects (Markov statistic second order) caused by the last two inserted monomer units can be assumed.

The molecular weights of ethene-norbornene copolymers, produced with various metallocene- and amidocyclopentadienyl-methylaluminoxane (MAO) catalysts, have been determined by high-temperature gel-permeation chromatography: with one exception, increasing molecular weights were found with an increasing norbornene content in the copolymer. This observation is due to the fact that the beta-hydride elimination process is not possible in the case of norbornene, because of special steric conditions of the cis-2,3-exo inserted norbornene; other possible termination reactions are discussed, considering the specialties of the norbornene. The effect of the catalyst structure on the molecular weights is discussed in terms of steric and electronic factors of the different ligands: sterically less hindered ligands produce ethene-norbornene copolymers with relatively low molecular weights; ligands with a larger extension and electron-pushing effect such as the fluorenyl ligand, induced the formation of high molecular weights. Additional alkyl groups at the indenyl or fluorenyl ligand increased the molecular weights additionally.

The copolymerization parameters of the ethene-norbornene copolymerization using various metallocene and half-sandwich catalysts were determined on the basis of composition data with linear graphical methods: Aside from r1 and r2, values for r11 and r21 could be determined in the case of alternating copolymerizations. In this connection, r21 differs significantly from catalyst to catalyst and reflects the different tendency of each catalyst to produce copolymers with an alternating monomer sequence. The maximum norbornene contents in the copolymer could be achieved by use of sterically less hindered metallocene catalysts. As an exception to this, the half-sandwich catalysts produced copolymers with surprisingly low norbornene contents.

The kinetics of the ethene-norbornene copolymerization using the [(isopropylidene)(eta5-inden-1-ylidene-eta5-cyclopentadienyl)]zirconium dichloride (iPr[IndCp]ZrCl2)/methylaluminoxane catalyst has been investigated at 70 degreesC in a concentrated solution of norbornene in toluene and an ethene pressure ranging from 4 to 60 bar (58-870 psi). The ethene reaction rate has been measured during the copolymerization process at varying reactant concentrations. The reaction orders and rate constants were determined and compared to the corresponding values of the ethene and norbornene homopolymerizations. It was found that kEhomo > kEco and kNhomo < kNco. The copolymerization parameters are r1 = 0.9 and r2 = 0.05.

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.