Chapter 1 describes the homopolymerization of styrene and the copolymerization of ethylene and styrenic comonomers mediated by the single-site bimetallic "constrained geometry catalysts" (CGCs), (µ-CH2CH2-3,3'){(η5-indenyl)[1-Me2Si(tBuN)](TiMe2)}2 [EBICGC(TiMe2)2; Ti2], (µ-CH2CH2-3,3'){(η5-indenyl)[1-Me2Si(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2; Zr2], (µ-CH2-3,3'){(η5-indenyl)[1-Me2Si(tBuN)](TiMe2)}2 [MBICGC(TiMe2)2; C1-Ti2], and (µ-CH2-3,3'){(η5-indenyl)[1-Me2Si(tBuN)](ZrMe2)}2 [MBICGC(ZrMe2)2; C1-Zr2], in combination with the borate activator/cocatalyst Ph3C+B(C6F5)4- (B1). Under identical styrene homopolymerization conditions, C1-Ti2 + B1 and Ti2 + B1 exhibit ～65 and ～35 times greater polymerization activities, respectively, than does monometallic [1-Me2Si(3-ethylindenyl)(tBuN)]TiMe2 (Ti1) + B1. C1-Zr2 + B1 and Zr2 + B1 exhibit ～8 and ～4 times greater polymerization activities, respectively, than does the monometallic control [1-Me2Si(3-ethylindenyl)(tBuN)]ZrMe2 (Zr1) + B1. NMR analyses show that the bimetallic catalysts suppress the regiochemical insertion selectivity exhibited by the monometallic analogues. In ethylene copolymerization, Ti2 + B1 enchains 15.4% more styrene (B), 28.9% more 4-methylstyrene (C), 45.4% more 4-fluorostyrene (D), 41.2% more 4-chlorostyrene (E), and 31.0% more 4-bromostyrene (F) than does Ti1 + B1. This observed bimetallic chemoselectivity effect follows the same general trend as the electron density on the styrenic ipso carbon (D > E > F > C > B). Kinetic studies reveal that both Ti2 + B1 and Ti1 + B1-mediated ethylene + styrene copolymerizations follow second-order Markovian statistics and tend to be alternating. Moreover, calculated reactivity ratios indicate that Ti2 + B1 favors styrene insertion more than does Ti1 + B1. All the organozirconium complexes (C1-Zr2, Zr2, and Zr1) are found to be incompetent for ethylene + styrene copolymerization, yielding only mixtures of polyethylene and polystyrene. Model compound (µ-CH2CH2-3,3'){(η5-indenyl)[1-Me2Si(tBuN)][Ti(CH2Ph)2]}2 {EBICGC[Ti(CH2Ph)2]2; Ti2(CH2Ph)4} was designed, synthesized, and characterized. In situ activation studies with cocatalyst B(C6F5)3 suggest an η1-coordination mode for the benzyl groups, thus supporting the proposed mechanism. For ethylene + styrene copolymerization, polar solvents are found to increase copolymerization activities and coproduce atactic polystyrene impurities in addition to ethylene-co-styrene, without diminishing the comonomer incorporation selectivity. Both homopolymerization and copolymerization results argue that substantial cooperative effects between catalytic sites are operative. In Chapter 2, a series of 0-3 metal oxide-polyolefin nanocomposites is synthesized via in situ olefin polymerization using the metallocene catalysts C2-symmetric dichloro[rac-ethylenebisindenyl]zirconium(IV) (EBIZrCl2), Me2Si(tBuN)(η5-C5Me4)TiCl2 (CGCTiCl2), and (η5-C5Me5)TiCl3 (Cp*TiCl3) immobilized on methylaluminoxane (MAO)-treated barium titanate (BaTiO3), zirconium dioxide (ZrO2), 3 mol% yttria-stabilized zirconia (TZ3Y), 8 mol% yttria-stabilized zirconia (TZ8Y), sphere-shaped titanium dioxide (TiO2), and rod-shaped TiO2 nanoparticles. The resulting composite materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 13C nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimetry (DSC). It is shown by TEM that the nanoparticles are well-dispersed in the polymer matrix and each individual nanoparticle is surrounded by polymer. Electrical measurements reveal that most of the nanocomposites have leakage current densities ~ 10-8-10-6 A/cm2, and the relative permittivities of the nanocomposites increase as the nanoparticle volume fraction increases, with measured values as high as 6.1. At the same volume fraction, rod-shaped TiO2 nanoparticle-polypropylene nanocomposites exhibit greater relative permittivities than the corresponding sphere-shaped TiO2 nanoparticle-polypropylene nanocomposites. The energy densities of these nanocomposites are estimated to be as high as 9.4 J/cm3.

Last modified

• 08/30/2018

Creator

• Neng Guo

DOI

• https://doi.org/10.21985/N2TM7T

Subject

• Chemistry

Keyword

• Inorganic Chemistry

Date created

• 2007-10-01

Resource type

• Dissertation

Rights statement

• In Copyright