Ethylene pressure has been used to control the competition between isomerization (chain walking) and monomer insertion processes for ethylene coordination polymerization catalyzed by a palladium-alpha-diimine catalyst. The topology of the polyethylene varies from linear with moderate branching to "hyperbranched" structures. Although the overall branching number and the distribution of short-chain branching change very slightly, the architecture or topology of the polyethylene changes from linear polyethylene with moderate branches at high ethylene pressures to a hyperbranched polyethylene at low pressures.

The availability of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is currently limited because they are produced mainly by marine fisheries that cannot keep pace with the demands of the growing market for these products. A sustainable non-animal source of EPA and DHA is needed. Metabolic engineering of the oleaginous yeast Yarrowia lipolytica resulted in a strain that produced EPA at 15% of dry cell weight. The engineered yeast lipid comprises EPA at 56.6% and saturated fatty acids at less than 5% by weight, which are the highest and the lowest percentages, respectively, among known EPA sources. Inactivation of the peroxisome biogenesis gene PEX10 was crucial in obtaining high EPA yields and may increase the yields of other commercially desirable lipid-related products. This technology platform enables the production of lipids with tailored fatty acid compositions and provides a sustainable source of EPA.

A group of polyethylenes synthesized using palladium R-diimine catalysts were studied using 13 C NMR spectroscopy, intensity light scattering, dynamic light scattering, and viscometry. These catalysts are known to produce branched polyethylenes without R-olefin comonomers. The series of polymers studied were synthesized under conditions of varying ethylene pressure. The polymers are highly branched and completely amorphous and are thus soluble in common organic solvents at ambient temperatures. Light scattering determinations of the root-mean-square radius of gyration (Rg) and the molecular weight M of fractions eluting from a size exclusion chromatograph demonstrated that, at a given M, Rg decreased as ethylene pressure decreased. The hydrodynamic parameterssthe Stokes radius (RH) from dynamic light scattering and the intrinsic viscosity ([η])salso decreased. The change in Rg at a constant M results from the change in branching topology for the polymers synthesized at different ethylene pressures. The parameter Rg 2 /M varies by an order of magnitude for the polymers synthesized under ethylene pressures varying from 0.1 atm to 500 psi. However, the total branching (methyls per 1000 CH2) and the distribution of short branches (methyl, ethyl, propyl, etc.) determined by 13 C NMR remained essentially unchanged. These observations indicate the branching topology changes with polymerization pressure. Polymer topology varies from predominantly linear with many short branches at higher ethylene pressures to a densely branched, arborescent globular structure at very low ethylene pressures. Polymers synthesized at the lowest ethylene pressure studied, 0.1 atm, exhibited dilute solution parameters similar to those observed for dendrimers or many-armed stars, with R g/RH below unity, and a segment density approaching that of a hard sphere.

It is well-known that short-chain branching (SCB) reactions (intramolecular H-abstraction) play an important role in determining the properties of ethylene homopolymers produced under high pressure by free-radical polymerization. There is little information, however, regarding SCB mechanisms that occur during the synthesis of ethylene copolymers under similar reaction conditions. This work describes SCB structures for a wide range of ethylene copolymers of varying composition (ethylene with n-butyl acrylate (nBA), methyl acrylate (MA), vinyl acetate (VAc), n-butyl methacrylate (nBMA), acrylic acid (AA), and methacrylic acid (MAA)), as determined by proton, 13 C, and 2D NMR techniques. Close examination of the resonances reveals that for many (if not all) of these copolymers, a significant fraction of the SCBs contain comonomer as a result of CH2-radical to CH2 backbiting around a comonomer unit. In addition, SCBs are formed not only by hydrogen abstraction from CH2 polyethylene units but also by abstraction of hydrogen from the comonomer methine units. This latter mechanism does not occur during production of E/VAc, E/nBMA, or E/MAA but is important for E/AA and acrylate (E/MA and E/nBA) copolymers; for these systems 10-20% of the comonomer groups in the polymer are alkylated. Implications of these findings to the polymerization kinetics are discussed.

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Late transition metal catalysts bearing R-diimine ligands allow ethylene and R-olefin homoand copolymerizations to polyolefins with unprecedented structures. The polypropylenes made with these new late metal catalysts have very complex microstructures that include combinations of features not seen in any known polypropylenes. These unusual structures include long branches, branches on branches including isobutyl branches, and moderate highly variable levels of 1,3-enchainment leading to runs of methylenes in the backbone of many different well-defined lengths. These features vary with the nature of the catalyst used for polymerization and with the polymerization conditions. Many of the polypropylenes are made primarily by 1,2-insertions to give syndiotactic placements via chain end control. A mechanistic description of catalyst behavior has been developed to explain these observed microstructures.

α-Diimine complexes of palladium and nickel catalyze the polymerization of α-olefins to give new materials that range from low-T g elastomers to low-melting, partially crystalline polymers. The 1H and 13C NMR spectra of the resulting polymers have been assigned in detail. Many unique microstructural features of the complex polymers have been identified. Mechanistic models that involve the 1,2- and 2,1-insertion of the α-olefins, chain walking, and insertion at certain points along the chain have been constructed. The complex microstructures can be explained using a small set of rules for palladium catalysts which is expanded slightly to account for the nickel catalysts.

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