13C NMR Studies of Ethene/Norbornene Copolymers using 13C‐Enriched Monomers: Signal Assignments of Copolymers Containing Norbornene Microblocks of up to a Length of Three Norbornene Units

Ethene and norbornene were copolymerized at 0.8 bar ethene absolute pressure using metallocene catalysts that produce microstructures containing norbornene blocks, particularly rac-Me 2 Si[Ind] 2 ZrCl 2 /MAO, iPr[Cp-Flu]ZrCl 2 /MAO and iPr[CpInd]ZrCl 2 /MAO. Intensive 13 C NMR spectroscopic investigations of the obtained copolymers were performed and norbornene di- and tri-block sequences detected clearly. Several copolymerization experiments were carried out by using 13 C 1 -enriched ethane, or 13 C 5/6 -enriched norbornene, respectively. Thus, resonances of the norbornene carbon atoms C5/C6 and the ethene carbon atoms Ca/Cb, which overlap extensively in the 13 C NMR spectra, could clearly be differentiated. In addition, further copolymerizations with natural monomers were performed at 2 bar ethene excess pressure to investigate the influence of the monomer concentration on the microstructure. By comparing the 13 C NMR spectra of copolymers obtained under different conditions assignments of most resonances were achieved. These 13 C NMR studies made it possible to assign norbornene triblock resonances with differing stereochemical connections such as meso, meso and rac, meso which have not been mentioned in previous works. The results led to new insights about the copolymer microstructure and allow development of a scheme showing the ethene/norbornene microstructures depending on the various catalyst systems utilized, including the metallocenes iPr[(3-iPr-Cp)Flu]ZrCl 2 and iPr[(3-tert-But-Cp)Ind]ZrCl 2 which have been applied in previous publications.