Epitaxial crystallization of isotactic poly(4‐methyl‐pentene‐1)

The crystallization of isotactic poly(4‐methylpentene‐1) in its stable tetragonal crystal modification based on the 7₂ helix conformation was achieved on three different low molecular weight organic substrates and on polytetrafluoroethylene. The contact face was always the (100) face, although the details of the epitaxial relationships generated one, two, or even three chain axis orientations in the polymer epitaxial overgrowth. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3088–3097, 2000     

Mapping Acid‐Catalyzed Deprotection in Thin Polymer Films: Fluorescence Imaging Using Prefluorescent 7‐Hydroxycoumarin Probes

Summary: Fluorescent images that illustrate acid‐catalyzed tert‐butoxycarbonyl (tBoc) deprotection patterns in polymer films were obtained using fluorescent sensors based on 7‐hydroxycoumarin dyes. Three commercial 7‐hydroxycoumarins, which are highly fluorescent, become practically nonemissive upon protection of the 7‐hydroxyl position with tBoc. In thin polymer films, the protected “prefluorescent” probes can return to their deprotected, fluorescent states by reaction with catalytic amounts of photogenerated acid and mild heating.

Protected probes become highly fluorescent after acid‐induced deprotection.     

Study of [Thienylene-dialkoxy phenylene] Conjugated Materials

Summary: In this work we report on the electrochromic and optical studies of thin films of thienylene-dialkoxyphenylene. The films for the optical measurements were prepared by spin casting on glass and silicon substrates. Photoluminescence and absorption spectra were recorded in the temperature range from 300 K. The differences between the spectra of the polymer and the oligomer can be attributed to a higher mean conjugation length in the polymer than in the oligomer. We present also a first principles theoretical calculation which shows that the conjugated oligomer has an HOMO-LUMO energy around 2.0 eV, which is consistent with the experimental data.     

Dynamically Generated Inertia

A (Higgs vacuum)–(spacetime geometry) reciprocity principle is proposed and its consequences are explored. While it has been established that configurations of the spacetime metric tensor field, associated with acceleration with respect to local inertial frames, cause the vacuum to become thermalized, it is asserted that the converse is also possible. An appropriate thermal vacuum, through dynamical mass generation, can cause particles to propagate in a spacetime with a Minkowski metric, as if they were in a spacetime with a non-Minkowski metric. The two points of view are equivalent and interchangeable. Invoking the reciprocity principle in the case of the Unruh effect in an accelerated frame, a mechanism is analyzed whereby in the context of the minimal standard model a gradient in the vacuum expectation value of the Higgs field in the direction of acceleration produces an effective inertial force on an accelerated material body.     

Non-Destructive Analysis of European Cobalt Blue Glass Trade Beads

Chemical analyses were made of royal blue glass trade beads from two early 17th century, archaeological sites in southern Ontario, Canada and from a glass beadmaking house in Amsterdam, The Netherlands. The results confirm that these beads were all mixed alkali — lime — silica glasses, coloured with Co and with opaque varients opacified with Sn. The groupings by chemistry tend to segregate by bead shapes, so that oval beads group together and circular shaped beads group together. Although the 2 Canadian sites are about 190 km apart, they produced 2 different sets of oval beads of similar chemistry, possibly helping confirm the contemporaneity of the people at both sites. An As/Co atomic ratio of about two may fit with the possible source of Co as a cobalt-arsenide ore (of common name smaltite) from the Hartz Mountains of eastern Germany, a source not far from either Amsterdam or Venice, both well known glass beadmaking centres of the period.     

Hairy PEO‐Silica Nanoparticles through Surface‐Initiated Polymerization of Ethylene Oxide

Summary: The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles was performed in situ by the ring‐opening polymerization of the oxirane monomer initiated from the mineral surface using aluminium isopropoxide as an initiator/heterogeneous catalyst. Alcohol groups were first introduced onto silica by reacting the surfacic silanols with prehydrolyzed 3‐glycidoxypropyl trimethoxysilane. The alcohol‐grafted silica played the role of a coinitiator/chain‐transfer agent in the polymerization reaction and enabled the formation of irreversibly bonded polymer chains. Silica nanoparticles containing up to 40 wt.‐% of a hairy layer of grafted PEO chains were successfully produced by this technique.

The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles by in‐situ ring‐opening polymerization of the oxirane monomer.     

N-Heterocyclic Carbenes as Key Intermediates in the Synthesis of Fused,Mesoionic, Tricyclic Heterocycles

Coupling between 5-bromoimidazo[1,5-a]pyridinium salts and malonate or arylacetate esters leads to a facile and straightforward access to the new mesoionic, fused, tricyclic system of imidazo[2,1,5-cd]indolizinium-3-olate. Mechanistic studies show that the reaction pathway consists of nucleophilic aromatic substitution on the cationic, bicyclic heterocycle by an enolate-type moiety and in the nucleophilic attack of a transient free N-heterocyclic carbene (NHC) species on the ester group; the relative order of these two steps depends on the nature of the starting ester. This work highlights the valuable implementation of free NHC species as key intermediates in synthetic chemistry, beyond their classical use as stabilizing ligands or organocatalysts.     

H2O time histories in the H2-NO2 system for validation of NOx hydrocarbon kinetics mechanisms

The development and refinement of NOx chemical kinetic mechanisms have been instrumental in understanding and reducing NOx formation. However, relatively little work has been performed with NOx species as the oxidizer, and such experiments can provide unique insights into NOx kinetics. Furthermore, speciation data can often provide useful information that complements global measurements such as ignition delay times in facilitating mechanism refinement. To provide such speciation data in the H₂-NO₂ system, H₂O measurements were performed using a fixed-wavelength, direct absorption laser diagnostic near 1.39 µm behind reflected shock waves in fuel-lean, near-stoichiometric, and fuel-rich mixtures of H₂ and NO₂ highly diluted in argon. Experiments were performed between 917 and 1782 K near atmospheric pressure. The H₂O profiles obtained herein are markedly different from those using O₂ as the oxidizer obtained in a previous study. The GRI 3.0 mechanism was found to greatly underestimate the H₂O formation, whereas two modern mechanisms were found to predict the H₂O formation quite accurately except at colder temperatures for fuel-rich conditions. Explanations for the differences between these mechanisms are given and discussed, with the conclusion that older mechanisms such as GRI 3.0 should not be used to model hydrocarbon/NOx combustion chemistry as they are lacking several key reactions and species, namely NO₃ and HONO. The discrepancy between models and data at lower temperatures could not be reconciled even when modifying two of the most-sensitive reaction rates. To the best of the authors’ knowledge, this study presents the first shock-tube speciation study in the H₂-NO₂ system.