Browsing by Author "Gurram, Venkata Narayana"

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    Novel early and late transition metal complexes for the synthesis of functional vinyl-insertion and metathesis polymerization-derived block-copolymers
    (2012) Gurram, Venkata Narayana; Buchmeiser, Michael R. (Prof. Dr.)
    The first chapter of this thesis deals with a general introduction to polyolefins and the historical development of Ziegler-Natta catalysis as well as with homogeneous catalysis. Furthermore, their applications in the field of polymer chemistry are outlined. Also, the chemistry of Grubbs- and Schrock-type catalysts and their reactivity in metathesis and the intercorrelation between Ziegler-Natta and metathesis chemistry is described. The second chapter deals with the synthesis and reactivity of a series of novel Ru-alkylidene-based initiators, in which both chloride ligands were replaced by pseudo-halides or by nitrate, i.e. [Ru(NCO)2(IMesH2)(C5H5N)(CHC6H5)] (1b), [Ru(CF3SO3)2(IMesH2)(C5H5N)(CHC6H5)] (1c), [Ru(NCO)(CF3SO3)(IMesH2)(C5H5N)(CHC6H5)] (1d), [Ru(CF3SO3)(CF3CO2)(IMesH2)(C5H5N)(CHC6H5)] (1e), [Ru(NCS)2(IMesH2)(C5H5N)(CHC6H5)] (1f), [Ru(NO3)2(IMesH2)(CH-2-(2-PrO)-C6H4)] (2d) and [Ru((CF2)3(CO2)2)(IMesH2)(CH-2-(2-PrO)(C6H4)] (2f), (IMesH2=1,3-dimesitylimidazolin-2-ylidene). The novel initiators and those of the general formula [RuX2(L)n(NHC)(CHPh)] and [RuX2(NHC)(CH-2-(2-PrO)-C6H4)] (X=Cl, C6F5COO; NHC=IMesH2, 1,3-dimesitylpyrimidin-2-ylidene, 1,3-dimesityldiazepin-2-ylidene, 1-mesityl-3-(2-phenylethyl)imidazolin-2-ylidene, 1-mesityl-3-adamantylimidiazolin-2-ylidene; L=PCy3, pyridine, n=1, 2) were investigated for their propensity to copolymerize norborn-2-ene (NBE) with cyclopentene (CPE) and cis-cyclooctene (COE), respectively, in an alternating way. Alternating copolymers, that is, poly(NBE-alt-CPE)n and poly(NBE-alt-COE)n containing up to 55 and 40% alternating diads, respectively, were obtained. Moreover, Ru(CF3COO)2(1,3-dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene)(=CH-2-(2-PrO)C6H4) (4b) turned out to be a highly efficient initiator for the homopolymerization of cyclopentene (CPE), allowing for the synthesis of high-molecular weight poly(CPE). Some fundamental effects of the nature of the pseudo-halide ligand on the extent of alternating copolymerization of NBE with CPE or COE are presented. Finally, the effects of the ring-size of the N-heterocyclic carbene on the configuration of the double bonds in the final polymer are addressed. The 3rd chapter deals with novel ZrIV-complexes of the type (Me2Si((NR)(6-(2-(diethylboryl)phenyl)pyrid-2-yl))ZrCl2.THF; R= tBu (13), adamantyl (17)) and TiIV-based metallocene-type complexes i.e. bis((N(6-(2-(diethylboryl)phenyl)-pyrid-2-yl)Me)TiCl2 (24) and non-bridged half-titanocene complexes of the type Cp'TiCl2(N(6-(2-(diethylboryl)phenyl)-pyrid-2-yl)R); R=Me (22, 23), Si(CH3)3 (26, 27), Cp'=Cp (22 and 26), Cp* (23 and 27) as well as with the chemistry of the aminoborane-free model complexes Cp'TiCl2(N-(biphenyl-3-yl)R); R= SiMe3 (30, 31), Me (33, 34), (Cp'=Cp (30, 34), Cp* (31, 33)); (Figure 2). These Zr- and Ti-complexes were characterized by 1H and 13C NMR spectroscopy and elemental analysis. The molecular structures of complexes 22, 23, 27 and 34 were determined by single-crystal X-ray diffraction. Upon activation with MAO, complexes 13, 17, 22, 23, 26 and 27 show activities up to 3000 kg-PE /mol-M.h in the homopolymerization of ethylene (E), producing mainly linear poly(ethylene) (PE) (HDPE) with molecular weights in the range of 100,000 < Mn < 4 x 106 g mol-1. Surprisingly, in the copolymerization of ethylene (E) with CPE, complex 13 exhibits high catalytic activity (30,000 kg-PE /mol-Zr.h), producing poly(E)-co-poly(CPE)VIP with 3-4 mol-% of vinyl addition polymer incorporated CPE. In the copolymerization of E with NBE, complexes 13, 17, 22, 23, 26 and 27 mainly produced vinyl addition copolymerization-derived poly(E)-co-poly(NBE)VIP with incorporated NBE-fractions of up to 36 mol-% as evidenced by 13C NMR analysis. Interestingly, at low E pressures (2 bar) and higher NBE concentrations, complex 23/MAO produced reversible ROMP- and VIP-derived copolymers of NBE with E, resulting in the formation of poly(NBE)ROMP-co-poly(NBE)VIP-co-poly(E). This particular copolymer formation can be explained by a reversible α-H elimination/ α-H addition process during the polymerization and is attributed to the unique role of the 6-[2-(diethylboryl)phenyl]pyrid-2-yl ligand moiety in this complex. The catalytic activity of Zr-based complexes for the copolymerization E with NBE was lower than that for E homopolymerization. The ZrIV-based and non-bridged half-titanocenes complexes derived E-NBE copolymers possessed alternating it E-NBE sequences and st E-NBE sequences along with isolated NBE sequences. Several minor signals at 21.2, 31.0, 33.5 and 41.1 ppm appeared, due to the result of NN diads in high content of NBE (>10 mol-%) copolymers. The incorporation of NBE in the resulting copolymers was highly influenced by the E pressure, mainly at low pressures (1 or 2 bar E) the NBE content was high in the resulting copolymers. The influence of the NBE feed also exhibits impact on both the catalytic activity and NBE incorporation as well as on the number-average molecular weights of the resulting copolymers. While increasing the NBE feed, the catalytic activity decreased. Similarly, the number-average molecular weight increased in the resulting E-NBE copolymer. Copolymers with low NBE incorporation (<10 mol-%) possessed only alternating st E-NBE sequences along with isolated NBE sequences without any alternating it E-NBE sequences and NBE diads. Copolymers with a high NBE content (>10 mol-%) possessed both alternating it and st E-NBE sequences as well as isolated NBE sequences with some minor NBE diads resonances. In addition, the homopolymerization of styrene was investigated using the non-bridged half-titanocene complexes 26 and 27 containing the 6-[2-(diethylboryl)phenyl]-pyrid-2-yl motif, as well as the aminoborane-free non-bridged half-titanocene complexes 30 and 31 at various conditions in the presence of MAO as co-catalyst. The study revealed that catalytic activities increased upon increasing the polymerization temperatures. Complexes bearing the 6-[2-(diethylboryl)phenyl]-pyrid-2-yl motif exhibited lower activities (up to 1100 kg.sPS/molcatalyst.h) when compared with aminoborane-free non-bridged half-titanocene complexes (up to 3500 kg.sPS/molcatalyst.h) and all these complexes mainly produced syndiotactic poly(styrene) with number-average molecular weights in the range of 29,000 < Mn < 1.4 x 105 g/mol.