Microstructural characteristics and thermal properties of ansa-zirconocene catalyzed copolymers of propene with higher α-olefins



Copolymers of propene and several higher α-olefins, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 4-methyl-1-pentene (4M1P), have been prepared with two different metallocene catalysts, rac-Et(Ind)2ZrCl2 (EI) and rac-Me2Si(2-MeBenz-[e]Ind)2ZrCl2 (MBI), and comprehensively characterized by 13C NMR spectroscopy. All copolymers produced with EI have comparable isotacticities as well as similar stereosequences. The copolymers produced with MBI significantly differ both from the reference propene homopolymer and among themselves: in fact, they are characterized by rather low isotacticities and the degree of tacticity is strongly influenced by comonomer type and concentration. A detailed 13C NMR analysis revealed that these copolymers are constituted by highly isotactic and atactic sequences of various lengths. The similar thermal behavior, in terms of transition temperatures, for the homologues of the series obtained with the two different catalysts show that the capability of crystallization of these systems is not directly connected to the overall microstructural properties (e.g. the isotacticity index) but can be accounted for by the details of the microstructure.