Transition metal catalyzed polymerization of butadiene in supercritical CO{sub 2}

A class of Ni(II) catalysts has been shown to stereoselectively catalyze the 1,4-polymerization of butadiene. The authors have been investigating the use of supercritical CO{sub 2} as an environmentally benign replacement solvent for conventional hydrocarbon and halocarbon solvents for a variety of chemical transformations. Above 31 C, CO{sub 2} enters a supercritical phase, where its physical properties are both liquid-like and gas-like. Importantly, the solvent properties such as dielectric constant for supercritical fluids can be varied by changing the pressure of the fluid. In this report, the authors present results of an investigation of the polymerization of 1,3-butadiene using [({pi}-allyl) Ni(CF{sub 3}CO{sub 2})]{sub 2} in supercritical CO{sub 2}. They conducted 1,3-butadiene polymerizations in CO{sub 2} to determine whether or not they could systematically and predictably adjust the regiochemistry/stereochemistry of the polybutadiene product by varying the solution properties at different pressures. They also mention experiments with CO catalysts that are known to give 1,2-syndiotactic polybutadiene, and with a Pd catalyst system that is known to copolymerize olefin with CO to give perfectly alternating copolymers

Environmentally friendly polysilane photoresists

Several novel polysilanes synthesized by the free-radical hydrosilation of oligomeric polyphenylsilane or poly(p-tert- butylphenylsilane) were examined for lithographic behavior. This recently developed route into substituted polysilanes has allowed for the rational design of a variety of polysilanes with a typical chemical properties such as alcohol and aqueous base solubility. Many of the polysilane resists made could be developed in aqueous sodium carbonate and bicarbonate solutions. These materials represent environmentally friendly polysilane resists in both their synthesis and processing

Monolayered organosilicate toroids and related structures: a phase diagram for templating from block copolymers

Here we report the controlled generation of micelle-templated organosilicate nanostructures resulting from self-assembly of a block copolymer/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Variation of solution condition and the copolymer/organosilicate mixture composition generates widely different film morphologies ranging from toroids to linear features to contiguous nanoporous monolayers. The use of reactive organosilicates for block copolymer templation generates functional inorganic nanostructures with thermal and mechanical stability

Application of solvent-directed assembly of block copolymers to the synthesis of nanostructured materials with low dielectric constants

An inverse relationship: Mixtures of poly(dimethylacrylamide)-block-polylactide copolymer (PDMA-b-PLA) with organosilicate oligomers (PMSSQ) selectively sequestered into the PDMA phase form micelles and inverse micelles in solution depending on the solvent. The micellar structures are imprinted into the resulting cured organosilicate to give monoliths or assemblies of densely packed organosilicate nanoparticles, respectively

Spontaneous generation of hydrogen peroxide from aqueous microdroplets

© 2019 National Academy of Sciences. All rights reserved.We show H2O2 is spontaneously produced from pure water by atomizing bulk water into microdroplets (1 μm to 20 μm in diameter). Production of H2O2, as assayed by H2O2-sensitve fluorescence dye peroxyfluor-1, increased with decreasing microdroplet size. Cleavage of 4-carboxyphenylboronic acid and conversion of phenylboronic acid to phenols in microdroplets further confirmed the generation of H2O2. The generated H2O2 concentration was ∼30 μM (∼1 part per million) as determined by titration with potassium titanium oxalate. Changing the spray gas to O2 or bubbling O2 decreased the yield of H2O2 in microdroplets, indicating that pure water microdroplets directly generate H2O2 without help from O2 either in air surrounding the droplet or dissolved in water. We consider various possible mechanisms for H2O2 formation and report a number of different experiments exploring this issue. We suggest that hydroxyl radical (OH) recombination is the most likely source, in which OH is generated by loss of an electron from OH- at or near the surface of the water microdroplet. This catalystfree and voltage-free H2O2 production method provides innovative opportunities for green production of hydrogen peroxide11sciescopu

Expanding the scope of nanostructures possible from block copolymers: role of selective deposition solvent

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