Unprecedented rhodium-catalyzed stereoselective polymerization of "carbenes" from ethyl diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear, neutral [(N,O-ligand)M(I)(cod)] (M = Rh, Ir) catalytic precursors for this reaction are characterized by (among others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from EDA: carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone. The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates are also polymerized. Further studies are underway to reveal possible applications of these new materials.
Kinetics-based differences
in the early stage fragmentation of
two structurally analogous silica-supported hafnocene- and zirconocene-based
catalysts were observed during gas-phase ethylene polymerization at
low pressures. A combination of focused ion beam-scanning electron
microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy
(IR PiFM) revealed notable differences in the distribution of the
support, polymer, and composite phases between the two catalyst materials.
By means of time-resolved probe molecule infrared spectroscopy, correlations
between this divergence in morphology and the kinetic behavior of
the catalysts’ active sites were established. The rate of polymer
formation, a property that is inherently related to a catalyst’s
kinetics and the applied reaction conditions, ultimately governs mass
transfer and thus the degree of homogeneity achieved during support
fragmentation. In the absence of strong mass transfer limitations,
a layer-by-layer mechanism dominates at the level of the individual
catalyst support domains under the given experimental conditions.
Synthesis, ethene/1-hexene copolymerization screening, and QSAR study of 28 silicon bridged (2-indenyl)(1-indenyl) zirconocenes: new promising catalysts for LLDPE were identified.
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