Taito Väänänen

Microstructural analysis of polypropylenes produced with heterogeneous Ziegler-Natta catalysts

Abstract Microstructural analysis was carried out on five isotactic polypropylenes produced with different heterogeneous Ziegler-Natta catalyst systems and different polymerization processes. The samples were fractionated according to stereostructure using a direct extraction method. Pentad tacticities of unfractionated samples and selected fractions were determined by 13 C n.m.r. spectroscopy. I.r. isotacticities were also measured. Statistical analysis of the polymerization mechanism was carried out on the basis of the two-site model from the pentad tacticities, and average lengths of meso and racemic sequences were determined. In addition to atactic and isotactic materials produced at different catalytic sites, the polypropylene samples contained syndiotactic material as stereoblocks in isotactic chains. On the basis of the analysis carried out on the fractions, slight differences in the microstructure were found to exist between the samples produced by different processes and catalyst types. These differences have a significant effect on average sequence lengths.

Two-site model analysis of 13C n.m.r. of polypropylene polymerized by Ziegler-Natta catalyst with external alkoxysilane donors

Abstract Two-site model analysis was carried out for 13 C n.m.r. of polypropylene polymerized by Ziegler-Natta catalyst with external alkoxysilane donors. Four effects of the external donors were found: selective poisoning of symmetric site; transformation of a symmetric to an asymmetric (but fluctuating) site; increase of whole isotacticity due to that of polymers obtained by the fluctuating site; and increase of isotacticity of the polymers obtained by the fluctuating site when the concentration of external donor is high enough.

Influence of polymerization conditions on microstructure of norbornene-ethylene copolymers made using metallocene catalysts and MAO

When characterized with 13C-NMR, it was found that norbornene-ethylene copolymers had a more complicated microstructure when dimethylsilyl bis(indenyl) zirconium dichloride was used as the catalyst compared to ethylene bis(indenyl) zirconium dichloride. One could see more block sequences but less alternating sequences. For both catalysts the highest amounts of block sequences were obtained for high norbornene concentrations, medium to high Al/Zr ratios, and low polymerization temperatures. There were also more alternating sequences for high norbornene concentrations and high polymerization temperatures. The isolated norbornene units (separated by more than one ethylene unit) were all exoconfiguration. No unsaturation was seen.

Effects of the Structure of External Alkoxy Silane Donor in High Activity Ziegler-Natta Catalyst on the Microstructure of Polypropylene

Correlations were sought between the structure of external alkoxy silane donors and the microstructure of the obtained polymer chain. Propylene was polymerized in liquid monomer with a heterogeneous high activity Ziegler-Natta catalyst. Fifteen different alkoxy silanes of structure R n Si(OR′) 4-n , where n=1–3, R = Ph or alkyl and R′ = C 1–3 alkyl, were used as external donors. Polymers were fractionated by boiling heptane extraction. Microstructures of the polymers were studied by means of 13 C NMR.