Abstract
Summary: Video microscopy as a tool for investigating olefin gas phase copolymerization is presented for the first time in this paper. The central theme of this work is the study of the comonomer effect shown by an unbridged metallocene catalyst supported on silica. By using video microscopy, it is possible to observe the increase in catalytic activity in terms of particle growth as well as monomer consumption. The observation that a more pronounced induction period in the particle growth profile is shown with increasing propylene concentration led us to investigate the copolymers obtained at different polymerization times using ^13^C NMR analysis and single particle energy dispersive Xβray (EDX mapping). This allowed us to adapt the βpolymer growth and particle expansion modelβ to the copolymerization. Besides physical causes for the comonomer effect, we wanted to determine whether the catalyst structure plays an important role in the comonomer effect. To this end we investigated two metallocenes bearing the same long bridging unit but differing in the ligand bound to the zirconium center. One metallocene bears a cyclopentadienyl ring, while the other bears an indenyl group. From a close analysis of the ^13^C NMR, it is clear that both catalysts insert ethylene more easily then propylene, probably due to the long bridging unit that results in a narrower aperture angle of the ligand. In addition to this, the indenyl ligand does not allow the formation of propylene blocks even at high propylene concentration.
Snapshot of the polymer particles taken after 165 min of ethyleneβ1βbutene copolymerization with catalyst 1.
imageSnapshot of the polymer particles taken after 165 min of ethyleneβ1βbutene copolymerization with catalyst 1.