The first acyclic diene metathesis (ADMET) polymerization using the molybdenum catalyst Mo(CHCMesR) (N-2,6-CeH3-i-Pr2) [OCCHsiCFslz] 2 (R = Me, Ph) is presented. This catalyst is much faster in the metathesis of terminal olefins than its tungsten counterpart. 1,4-Benzenedicarboxylic bis(l-hexenyl) ester, 1,4-benzenedicarboxylic bis(l-pentenyl) ester, 1,4-benzenedicarboxylic bis(l-butenyl) ester, and 1hexenyl 1-pentenoate successfully undergo ADMET homopolymerization. These polymerizations are initiated under bulk conditions and are continued in solution to produce poly[oxy-5-decenyloxyterephthaloyl], poly-[oxy-4-octenyloxyterephthaloyl], poly[oxy-3-hexenyloxyterephthaloyl], and poly(oxy-3-octenyl ester), respectively. No metathesis activity is observed for 1,4-benzenedicarboxylic bis(l-propenyl) ester or 1-hexenyl 1-butenoate due to the negative neighboring group effect. This negative neighboring group effect involves either the coordination of the carbonyl oxygen to the metal center or simply the polarization of the double bond such that the intermediates of the metathesis process are not favored. The copolymerization of 1,4benzenedicarboxylic bis(l-pentenyl) ester and 1,9-decadiene produces a random copolymer. All polymer structures were determined by IR, NMR, and 13C NMR spectroscopy, and number-average molecular weights were determined by end-group analysis and vapor-pressure osmometry. Synthesis, characterization, and the general limitations of this polymerization are discussed.

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Currently, carbon fibers (CFs) from the solution spinning, air oxidation, and carbonization of polyacrylonitrile impose a lower price limit of ≈$10 per lb, limiting the growth in industrial and automotive markets. Polyethylene is a promising precursor to enable a high-volume industrial grade CF as it is low cost, melt spinnable and has high carbon content. However, sulfonated polyethylene (SPE)-derived CFs have thus far fallen short of the 200 GPa tensile modulus threshold for industrial applicability. Here, a graphitization process is presented catalyzed by the addition of boron that produces carbon fiber with >400 GPa tensile modulus at 2400 °C. Wide angle X-ray diffraction collected during carbonization reveals that the presence of boron reduces the onset of graphitization by nearly 400 °C, beginning around 1200 °C. The B-doped SPE-CFs herein attain 200 GPa tensile modulus and 2.4 GPa tensile strength at the practical carbonization temperature of 1800 °C.

The first acyclic diene metathesis (ADMET) polymerization of carbonate containing monomers using the molybdenum catalyst, Mo(CHCMeiPh)(N-2,6-CeH8-t-Pri)[OCCHgiCFalz]z is reported. Bis(lhexenyl) carbonate, bis(l-pentenyl) carbonate, bis(l-butenyl) carbonate, and 4,4'-isopropylidenebis(phenyl 1-butenyl carbonate) successfully undergo ADMET homopolymerization. These polymerizations are initiated under bulk conditions and are continued in solution to produce poly(5-decenyl carbonate), poly(4-octenyl carbonate), poly(3-hexenyl carbonate), and poly(oxycarbonyloxy-l,4-phenyleneisopropylidene-l,4-phenyleneoxycarbonyl-l,6-hex-3-enylene), respectively. No metathesis activity is observed for bis(l-propenyl) carbonate due to a negative neighboring group effect. This effect involves either the coordination of the carbonyl oxygen to the metal center or simply the polarization of the double bond such that the intermediates of the metathesis process are not favored. All polymer structures were characterized by IR, NMR, and 13C NMR spectroscopy. Number-average molecular weights were determined by end-group analysis and vapor pressure osmometry. Synthesis, characterization, and the general limitations of this polymerization are discussed.

This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) precursor that relates tensile modulus to the elastic properties and angular distribution of constituent graphitic layers, as measured using wide-angle x-ray diffraction of individual carbon fiber filaments. The observed relationship and interpretation of data using a uniform-stress model has revealed fundamental differences in the nature of the microstructure present in carbon fiber produced from polyethylene compared to carbon fiber produced from polyacrylonitrile (PAN) or pitch precursors. Specifically, it was found that the shear modulus, indicative of the shear between adjacent graphitic layers of the carbonized fiber is lower for polyethylene-derived carbon fiber than for PAN-or pitch-derived carbon fiber, suggesting that the covalent CC sp 3 crosslink density connecting adjacent graphitic layers in PE-derived carbon fiber is reduced. This structure that is less crosslinked is anticipated to be easier to orient during carbonization and high-temperature graphitization processes, yielding a highly oriented structure necessary for high tensile modulus.

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The novel constrained geometry complexes [η5:η1-C5H4EMe2−SiMe2−N(t-Bu)]TiX2, 5a (E = C, X = Cl), 5b (E = C, X = Me), 6a (E = Si, X = Cl), and 6b (E = Si, X = Me), based on dimethylcyclohexadienyl and dimethylsilacyclohexadienyl ligands have been prepared and characterized by 1H and 13C{1H} NMR spectroscopy and single-crystal X-ray structure analysis (5a and 6a). These complexes are the first examples of compounds containing η5 “open” dienyl ligands (pentadienyl or cyclohexadienyl) for titanium in its highest (4+) oxidation state. The crystallographic and electrochemical analysis of these complexes demonstrate that “open” dienyl ligands can be used as a viable replacement for the cyclopentadienyl ring in complexes containing a pendant amido group.