13C NMR Study of Copolymers of Propene with Higher 1-Olefins with New Microstructures by ansa-Zirconocene Catalysts

Copolymers of propene and higher 1-olefins (1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and 4-methyl-1-pentene (4M1P)), prepared with rac-Et(Ind)2ZrCl2 (EI) and rac-Me2Si(2-MeBenz-[e]Ind)2ZrCl2 (MBI), were comprehensively analysed by 13C NMR spectroscopy. These catalysts known to produce isotactic polypropene lead to two vastly different families of copolymers under the chosen experimental conditions. All copolymers produced with EI possessed comparable isotacticities as well as similar stereosequences. Furthermore, these copolymers did not significantly differ from those of the reference propene homopolymer. However, the copolymers produced with MBI significantly differed both from the reference propene homopolymer and among themselves. In fact, in contrast to the corresponding highly isotactic homopolymer, the whole series of copolymers was characterized by rather low isotacticities. The degree of tacticity was strongly influenced by the comonomer type. A detailed 13C NMR analysis revealed that these copolymers are constituted by highly isotactic sequences and by atactic sequences of various lengths. It is proposed that the formation of atactic sequences is triggered by the insertion of a comonomer. It seems likely that MBI can shift from a stereoselective to a nonstereoselective state due to an interaction with higher linear or branched comonomer.