Homogeneous Ziegler-Natta catalysis: Synthetic, kinetic, and thermodynamic studies examining olefin polymerization catalyst formation and behavior | Posted on:2000-11-12 | Degree:Ph.D | Type:Thesis | University:Northwestern University | Candidate:Beswick, Colin Lee | Full Text:PDF | GTID:2461390014961625 | Subject:Chemistry | Abstract/Summary: | | The following dissertation examines the synthesis and energetics of L 2MR+ B(C6F5)2Ar − systems in relation to their importance as active catalysts for olefin polymerization. Generally, formation of the complexes involves as in: L2M(Me)R + B(C6F5)2Ar → L2MR+ B(C6F5)2Ar −. Abstraction enthalpies are measured in toluene solution by titration calorimetry and variable-temperature 1H NMR. Dynamic reorganization that symmetrizes the ion-pair is also investigated by variable-temperature 1H NMR experiments over a wide solvent and temperature range.; The metals investigated are predominantly M = Zr and Hf, although some examples of M = Ti are included. Zirconium complexes are generally more synthetically accessible, have more favorable formation energies, looser ion-pairing, and greater olefin polymerization activities than comparable Hf complexes. Stabilization of the metal cation and promotion of loose ion-pairing is best obtained with ancillary ligations and substituents most capable of offering electron density and steric protection to the metal center. For instance, ligation such as L2 = (Me5Cp)2 is more stabilizing than L 2 = Cp2, and R = CH(TMS)2 is more stabilizing than R = Me. Formation of cation-anion pair structures is also investigated as a function of the strength of the B(C6F5)2Ar Lewis acid and the solvent dielectric constant. Increasing the electron withdrawing ability of the Ar group from Ar = C6H5 to C6F as do increases in solvent dielectric constant. | Keywords/Search Tags: | Olefin polymerization, Formation | | Related items |
| |
|