Propene/4-methyl-1-pentene copolymers by metallocene based catalysts: first insight in 13 C NMR assignment

A thorough C-13 NMR analysis of a series of propene/4-methyl-1-pentene copolymers, prepared with the isoselective metallocene precatalyst [rac-(EBTHI)ZrCl2], has paved the way to the first full description of such potentially interesting family of copolymers at the triad level. Several tetrads and even longer sequences were assigned and quantified as well. The main problem, consisting in the partial overlap of the resonances of the alpha alpha-methylenes of the chain and the alpha-methylenes of the branch, generally utilized for the microstructural description of propene/linear higher alpha-olefins copolymers, was overcome by analyzing other less informative regions of the spectra along with the application of two-dimensional heteronuclear (H-1-C-13) correlation measurements. A computational procedure for checking the correctness of the proposed assignments was applied to the C-13 NMR observed integrals of two samples differing in comonomer compositions. In both cases, a correspondence between the observed and calculated values of the sequence molar fractions was found.