Techn. Hochsch., Diss., 2000--Aachen.

Magdeburg, Universiẗat, Diss., 2003.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Universiẗat, Diss., 2005--Hamburg. / Erscheinungsjahr an der Haupttitelstelle: 2004.

Techn. Universiẗat, Diss., 2004--Berlin.

No description available.

No description available.

The thermodynamic parameters associated with the copolymerization of ethylene and carbon dioxide were calculated using bond dissociation energies, the Benson additivity method and density functional theory calculations (DFT). In all cases, the formation of an alternation copolymer was found to be endergonic at any reasonable polymerization temperatures (the ceiling temperature is calculated to be -159 °C). However, the polymerization was calculated to be exergonic at room temperature, as long as the incorporation of CO2 is less than 29.7 mol%. Experiments failed to provide evidence of any CO2 incorporation, despite previously published reports claiming up to 30 mol%. Octamethyloctahydrodibenzofluorenyl (Oct) has profound steric consequences when incorporated into metallocene olefin polymerization catalysts – including increased catalytic activity and stereoselectivity. However, the electronic effect of the ligand’s four electron-donating tertiary alkyl groups is less understood. NMR and DFT calculations were used to study the electronic nature of the Oct moiety – both as a part of ansa-metallocene pre-catalysts and as an independent molecule. The results show that Oct is more electron rich than other cyclopentadienyl analogues and that the electronics of the ligand are readily conveyed to the metal center. Upon activation, the steric bulk of the Oct moiety dominates the immediate environment around the metal center. Evidence is presented that supports previous theories about Oct’s ability to influence the counteranion distance, thereby increasing the catalytic activity. In addition, excess trimethyl aluminum (TMA) is known to be detrimental to catalytic activity and results uphold this belief – although the magnitude of the effect varies depending on the metallocene being studied. However, UV-Vis data do not support the theory that TMA binds to the catalytically-active metal center, thereby decreasing the catalytic activity; but does not offer an alternate mechanism.

The heterogeneous metallocene catalyst is becoming a very competitive industrially due to its ability to produce tailor-made polymers. The main advantage of the metallocene polymer product is the narrow molecular weight distribution (MWD) and the systematic comonomer distribution along the polymer chains. Therefore, the metallocene polymer product has well-defined mechanical and optical properties. The aim of this thesis is to investigate the effects of the silica support on the reaction kinetics and micro properties of the heterogeneous metallocene catalyst system. These investigations include studying the influence of the pore volume, surface area, particle size distribution, and the surface chemical characteristics of silica support on the catalyst performance. The experiments showed that the silica type has an influence on the kinetic behavior. For instance, silica with a lower pore volume shows an induction period when compared with higher pore volume silicas. Moreover, the silica type has a clear influence on catalyst activity and polymer morphology. The smallest silica particles produced the highest activity among the other sizes regardless of silica type. The supported catalysts were characterized and linked to the silica type and size in terms of catalyst activity and polymer morphology. Each catalyst in terms of silica type behaved similarly regardless of type of alkylaluminum used in the formulation. The micro properties of the produced polymers, such as MWD and chemical composition distribution (CCD), were studied to understand the effects of the type and size of silica support and co-catalyst on these properties. The silica types showed no effect on the MWD, but had a slight effect on the CCD. Silica with a high pore volume had a stronger more comonomer response. However, the silica particle size had an influence on the CCD, with less comonomer incorporation observed with smaller silica particles. Finally, triethylauminum was observed to produce polymer with a different MWD when compared with other alkylaluminums. However, all alkylaluminums used in this work had no effect on the CCD of the produced polymer regardless of silica type. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-04-11 13:37:09.878

Techn. Universiẗat, Diss., 2000--Darmstadt.