C-13 NMR-STUDIES OF ETHYLENE-PROPYLENE COPOLYMERS PREPARED WITH HOMOGENEOUS METALLOCENE-BASED ZIEGLER-NATTA CATALYSTS

The recent discovery of homogeneous metallocene-based Ziegler-Natta ca talysts has led to the synthesis of EP copolymers with new comonomer a nd stereochemical structures. In the present paper C-13 NMR investigat ion of EP copolymers at high ethylene content, prepared with highly is ospecific, highly syndiospecific, and aspecific catalysts, is presente d. The high stereoregularity of the iso- and syndiotactic samples and the complete regioregularity of all three samples greatly simplify the spectra and make it possible to check some of the chemical shift pred ictions and to perform other sequence assignments. The assignment of n ew sequences is based on (i) correlation of chemical shifts of homo- a nd copolymers performed with the same catalysts, (ii) comparison of sp ectral intensities for samples of different compositions, and (iii) co mparison with chemical shift values predicted by calculations. The det ailed information obtained on comonomer and tactic sequences opens the possibility of describing the chain growth mechanism for the various catalytic systems and of correlating chain structure and copolymer phy sical and mechanical properties.