Control of reaction mechanisms in cationically polymerized epoxy resins facilitates the adjustment of morphology and mechanical properties

Structure–property relations of cationically polymerized epoxy thermosets with different morphologies are examined. The morphology adjustment of amorphous epoxy based copolymers and partially crystalline polymer alloys is carried out with star‐shaped poly(ε‐caprolactone) (SPCL) bearing various numbers of hydroxyl end groups. These hydroxyl groups are known for their reactivity toward epoxides following the activated monomer (AM) mechanism. For this reason, four‐armed SPCL was synthesized with four hydroxyl end groups (SPCL‐tetraol) and, in addition, with successively esterified ones down to a SPCL with four ester end groups (SPCL‐tetraester). SPCL species bearing fewer or no hydroxyl end groups segregate into needle‐like nanodomains within the epoxy networks and, if the concentration is high enough, also into crystalline domains. The stronger phase separation of SPCL‐tetraester within the epoxy network compared with SPCL‐tetraol is due to a reduction of the AM mechanism. The mechanical properties resulting from different morphologies lead to a trade‐off between higher storage moduli and T_g values in the case of the more phase separated (and partially crystalline) polymer alloys and higher strain at break in the case of the amorphous copolymers. Nevertheless, in both cases toughness is improved or at least kept on the same level as for the pure epoxy resin. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2188–2199     

Dehydration of Alkanones by Bare FeO+ Involves the ω/(ω − 1) Positions: Exclusion of Iron Carbenes as Intermediates. Preliminary Communication

Fourier-transform ion-cyclotron-resonance (FTICR) mass spectrometry has been used to uncover the mechanisms by which FeO⁺ dehydrates heptan-4-one ( 5a ) and nonan-5-one ( 6a ) in the gas phase. The study of isotopomeric ketones provides evidence that H₂O loss is not due to a 1,1-elimination, thus ruling out the intermediacy of high-valent iron-carbene species. Rather, H₂O is generated in a formal 1,2-elimination involving the ω/ω ? 1 positions of the alkyl chain (‘remote C? H bond activation’). In the consecutive alkene/H₂O elimination, the olefins (ethylene from 5a and propene from 6a ) originate from the terminal part of one alkyl chain, and the H-atom is transferred to the FeO⁺ moiety in the course of this process, builds up together with an H-atom from the ω/ω-1 position of the other alkyl chain the H₂O molecule. In either case, the O-atom of H₂O is provided by the FeO⁺ species.     

The 1:1 glycine zwitterion-water complex: An ab initio electronic structure study

More than a dozen stationary points on the potential energy surface for the 1:1 glycine zwitterion—water complex have been investigated at Hartree-Fock or MP2 levels of theory with basis sets ranging from split valence (4-31G) to split valence plus polarization and diffuse function (6–31 + + G**) quality. Only one true minimum (GLYZWM, C₁ symmetry) could be located on the potential energy surface. GLYZWM features a bridged water molecule acting as both a hydrogen bond acceptor and donor with the NH₃⁻ and CO₂⁻ units of the glycine zwitterion. The total hydrogen bond energy in GLYZWM is computed as 16 kcal/mol (MP2/6–31 ++ G** // 6–31 ++ G**, including corrections for basis set superpositions errors). The computed vibrational frequencies and normal mode forms of the GLYZWM complex resemble in many cases experimental assignments made for the glycine zwitterion in bulk water on the basis of Raman spectroscopy. © 1996 by John Wiley & Sons, Inc.     

Even-electron ions: a systematic study of the neutral species lost in the dissociation of quasi-molecular ions

The collision-induced dissociations of the even-electron [M + H](+) and/or [M - H](-) ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH(3), SO(3)H in the negative ion mode, or NO(2) in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH(2) in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H](+) and [M - H](-) ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even-electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS-QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even-electron [M + H](+) and/or [M - H](-) ions (generated by ESI or APCI) with that of the corresponding odd-electron [M](+) ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion.     

Novel Methods to Manipulate Autolysis in Sparkling Wine: Effects on Yeast

Sparkling wine made by the traditional method (Méthode Traditionelle) develops a distinct and desirable flavour and aroma profile attributed to proteolytic processes during prolonged ageing on lees. Microwave, ultrasound and addition of β-glucanase enzymes were applied to accelerate the disruption of Saccharomyces cerevisiae, and added to the tirage solution for secondary fermentation in traditional sparkling winemaking. Scanning electron microscopy and flow cytometry analyses were used to observe and describe yeast whole-cell anatomy, and cell integrity and structure via propidium iodide (PI) permeability after 6-, 12- and 18-months post-tirage. Treatments applied produced features on lees that were distinct from that of the untreated control yeast. Whilst control yeast displayed budding cells (growth features) with smooth, cavitated and flat external cell appearances; microwave treated yeast cells exhibited modifications like ‘doughnut’ shapes immediately after treatment (time 0). Similar ‘doughnut’-shaped and ‘pitted/porous’ cell features were observed on progressively older lees from the control. Flow cytometry was used to discriminate yeast populations; features consistent with cell disruption were observed in the microwave, ultrasound and enzyme treatments, as evidenced by up to 4-fold increase in PI signal in the microwave treatment. Forward and side scatter signals reflected changes in size and structure of yeast cells, in all treatments applied. When flow cytometry was interpreted alongside the scanning electron microscopy images, bimodal populations of yeast cells with low and high PI intensities were revealed and distinctive ‘doughnut’-shaped cell features observed in association with the microwave treatment only at tirage, that were not observed until 12 months wine ageing in older lees from the control. This work offers both a rapid approach to visualise alterations to yeast cell surfaces and a better understanding of the mechanisms of yeast lysis. Microwave, ultrasound or β-glucanase enzymes are tools that could potentially initiate the release of yeast cell compounds into wine. Further investigation into the impact of such treatments on the flavour and aroma profiles of the wines through sensory evaluation is warranted.     

Polar manifolds and actions

A group action is called polar if there exists an immersed submanifold (a section) which intersects all orbits orthogonally. We show how to construct a manifold admitting a polar group action by prescribing its isotropy groups along a fundamental domain in the section. This generalizes a classical construction for cohomogeneity-one manifolds.We give many examples showing the richness of this class of group actions and relate the topology of the section to the topology of the manifold.     

The continuity of superposition operators on some sequence spaces defined by moduli

Let λ and μ be solid sequence spaces. For a sequence of modulus functions Φ = (ϕ k) let λ(Φ) = {x = (x _k ): (ϕk(|x _k |)) ∈ λ}. Given another sequence of modulus functions Ψ = (ψ_k), we characterize the continuity of the superposition operators P _f from λ(Φ) into μ (Ψ) for some Banach sequence spaces λ and μ under the assumptions that the moduli ϕk (k ∈ ℕ) are unbounded and the topologies on the sequence spaces λ(Φ) and μ(Ψ) are given by certain F-norms. As applications we consider superposition operators on some multiplier sequence spaces of Maddox type. This research was supported by Estonian Science Foundation Grant 5376.     

On interpolatory divergence-free wavelets

We construct interpolating divergence-free multiwavelets based on cubic Hermite splines. We give characterizations of the relevant function spaces and indicate their use for analyzing experimental data of incompressible flow fields. We also show that the standard interpolatory wavelets, based on the Deslauriers-Dubuc interpolatory scheme or on interpolatory splines, cannot be used to construct compactly supported divergence-free interpolatory wavelets.

     

Embedded constant mean curvature surfaces with special symmetry

We give sharp, necessary conditions on complete embedded CMC surfaces with three ends and an extra reflection symmetry. The respective submoduli space is a two-dimensional variety in the moduli space of general CMC surfaces. Fundamental domains of our CMC surfaces are characterized by associated great circle polygons in the three-sphere. Received: 23 January 1998 / Revised version: 23 October 1998