The living ring-opening metathesis polymerization (ROMP) of trans-cyclooctene (tCO) was investigated. ROMP of tCO in the presence of PPh 3 in THF leads to the formation of narrowly dispersed polycyclooctene (PCO). The presence of PPh 3 as an additive and the use of THF as a solvent were demonstrated to be necessary to suppress competing secondary metathesis processes in the ROMP of tCO. Under optimal conditions, narrowly dispersed PCO was achieved without high molecular weight contaminates. The PCO was then hydrogenated to form linear, narrowly dispersed polyethylene with a melting temperature of 139 °C. Protected, hydroxy-functionalized tCO was polymerized by this method to afford narrowly dispersed, hydroxylated PCO. Block copolymers containing polynorbornene and PCO or containing differentially functionalized PCO were also synthesized and hydrogenated to form block copolymers containing blocks of linear, narrowly dispersed polyethylene.Ring-opening metathesis polymerization (ROMP) has been employed in the synthesis of a wide range well-defined polymer architectures. 1,2 ROMP is a chain-growth polymerization in which a cyclic olefin is converted to polymer. This process is driven by the release of ring strain which provides the main driving force that is required to overcome the unfavorable entropy change in polymerization. 3 Typical cyclic olefins for ROMP include norbornene, cyclobutene, cyclooctene, and dicyclopentadiene. Also, many functionalized derivatives of these monomers can be polymerized using the functional-group tolerant, late transition metal Grubbs' catalysts 1-3 (Figure 1). 3 In recent years, living ROMP has emerged as a valuable tool for polymer chemists. 4 A living ROMP polymerization is generally characterized by a low polydispersity index (PDI) < 1.1 and a linear relationship between polymer molecular weight and monomer conversion. [3][4][5] Norbornene and its functionalized derivatives have become the monomers of choice for living ROMP due to widespread commercial availability, low cost, and general ease of synthesis. Low polydispersity polymers are achieved with living ROMP when the rate of polymer chain initiation (k i ) occurs faster than chain propagation (k p ) 6 and competing secondary metathesis reactions (k s ), including inter-and intramolecular chain transfer by reaction of the initiator with olefins in the polymer backbone, are eliminated. Norbornene exhibits the characteristic high ring strain such needed for irreversible (k p ≫.k s ) ROMP ( Figure 2) and consequently produces polymers with low PDIs and controllable molecular weights with fast-initiating (k i /k p ≥ 1) catalysts 1 and 3. NIH Public Access Author ManuscriptMacromolecules. Author manuscript; available in PMC 2010 April 7. Secondary metathesis is limited by the steric hindrance of the olefins in the backbone of substituted polynorbornenes. In contrast, the living ROMP of monocyclic, unhindered alkenes has seen limited use. Cyclobutene and its functionalized derivatives have been used in living ROMP but to...

The syntheses of regioregular as well as stereoregular ethylene-vinyl alcohol (EVOH) copolymers by ring-opening metathesis polymerization (ROMP) with ruthenium catalysts are reported. Symmetric cyclooctenediol monomers were protected as acetates, carbonates, or acetonides to temporarily increase ring strain as well as impart solubility to the monomer. Polymer molecular weights could be easily controlled by either varying the monomer-to-catalyst ratio or by the addition of a chain transfer agent. Hydrogenation and subsequent deprotection of the ROMP polymers afforded the EVOH materials in high yields, and the structures were confirmed by 1H NMR and 13C NMR spectroscopies. Thermal properties of the corresponding EVOH copolymers are reported and suggest that differences in diol stereochemistry significantly affect the polymer morphology.

This report describes the low-temperature synthesis of nanocrystalline perovskite oxide, La 0.8 Sr 0.2 MnO 3 (LSM), using the ammonium acrylate salt precursor gel method that employs 3,3′,3′′-nitrilotripropionic acid (NTP) as the gelling agent. Due to its high degree of hydrogen bonding with water, NTP can absorb many times its own weight of water to yield a viscous liquid. Subsequent pyrolysis converts the mixture to the desired metal oxides. This preparative method has several advantages such as homogeneity, excellent control of stoichiometry, ease of handling, lower heating times and temperatures, and the production of uniform particle size and distribution. The synthesis of the LSM is achieved in as little as 10 hours (400 °C) with uniform distribution of particles that are 25 nm in size.

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