Ethylene-Norbornene Copolymers Prepared with Metallocene Based Catalysts: New Sequence Assignments by 13 C NMR

A series of ethylene-norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene (N)/ethylene (E) mole ratios. Copolymers were characterized by C-13 NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of C-13 NMR spectra of copolymers prepared with different norbornene content and the correlation between C-13 NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and raceme NN dyads were assigned.