The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - II. Fire behaviour

In this second of a series of two papers, the fire behaviour of halogen-free flame retarded polycarbonate (PC) blends with different impact modifiers was studied. The impact modifiers were acrylonitrile-butadiene-styrene (ABS), a poly(n-butyl acrylate) rubber (PBA) with a poly(methyl methacrylate) (PMMA) shell and two silicone-acrylate rubbers consisting of PBA with different amounts of polydimethylsiloxane (PDMS) and different shell materials (PMMA and styrene-acrylonitrile, SAN). The flame retardant was bisphenol A bis(diphenyl phosphate) (BDP). Flammability was determined by LOI and UL 94. The burning behaviour under forced flaming conditions was studied by cone calorimeter under different external irradiations and by pyrolysis combustion flow calorimeter measurements. The exchange of ABS with the pure acrylate rubber worsened flammability, while similar results were obtained in cone calorimeter measurements. The exchange of ABS with the silicone-acrylate rubbers is promising, particularly with higher amounts of PDMS. In flammability tests strongly enhanced LOI values were obtained and therefore silicone-acrylate rubbers look like promising alternatives for ABS.     

Density-and-temperature-dependent volume translation for the SRK EOS: 1. Pure fluids

A mathematical framework for applying a density-and-temperature-dependent volume translation in a thermodynamically consistent manner was developed. Volumetric equations of state (EOS)s that incorporate this translation procedure can be used to generate derived properties, such as fugacity and enthalpy departure, that are based on isothermal departure or residuals from ideal gas state conditions. This kind of translation serves to improve the original EOS and not simply act as a correlation for molar volumes. A density-and-temperature-modified translation of this type was applied to the Soave–Redlich–Kwong EOS and was shown to possess accuracy for saturation pressure predictions equivalent to the untranslated EOS, as well as greatly improved density predictions compared to what is available when using only constant valued translation. The EOS translated in this manner retains many of the important features of the untranslated EOS, such as explicit calculation of volume roots, while having the representation capabilities of substantially more complicated models, such as the extended virial equation of Benedict, Webb, Rubin, and Starling.     

Naphthyridines. Part 3: First example of the polyfunctionally substituted 1,2,4-triazolo[1,5-g][1,6]naphthyridines ring system

Treatment of 1,2,4-triazoles (1) with diethylmalonate in bromobenzene gave 1,2,4-triazolo-[1,5-a]pyridines 2. Chlorination of 2 using POCl₃/DMF (Vilsmeier reagent) led to the isolation of 7-chloro-6-formyl-1,2,4-triazolo[1,5-a]pyridine derivative 4, which reacted with the stabilized ylid 5 to afford 6-ethoxycarbonylvinyl-1,2,4-triazolo[1,5-a]-pyridines 6. Azidation of 6 yielded the corresponding azido compound 7, (Scheme 2). Reduction of 7 with Na₂S₂O₄ gave the corresponding 7-amino compound 8, which cyclized in boiling DMF to give the novel 1,2,4-triazolo[1,5-g][1,6]naphthyridines 9. On the other hand, reacting 7 with one equivalent of PPh₃ (aza-Wittig reaction) in CH₂Cl₂ gave 7-imino-phosphorane derivative 10, and subsequent cyclization in boiling DMF afforded the new 1,2,4-triazolo[1,5-g][1,6]naphthyridine derivative 11 (Scheme 3). However, treatment of 10 with phenyl isothiocyanate in 1,2-dichlorobenzene at reflux temperature gave the new 1,2,4-triazolo[1,5-g][1,6]naphthyridine derivative 14 (Scheme 4). Refluxing 6 with excess of a primary amines 15a,b in absolute. EtOH yielded the corresponding 7-alkyl-amino-1,2,4-triazolo[1,5-a]pyridines 16a,b. These obtained amines 16a,b underwent intramolecular heterocyclization in boiling DMF to give the novel 9-alkyl-1,2,4-triazolo[1,5-g][1,6]-naphthyridines 17a,b, in excellent yields (Scheme 5).     

Absolute Configuration of Small Molecules by Co‐Crystallization

The most reliable method to determine the absolute configuration of chiral molecules is X‐ray crystallography, but small molecules can be difficult to crystallize. We report rapid co‐crystallization of tetraaryladamantanes with small molecules as different as n‐decane to nicotine to produce crystals for X‐ray analysis and the assignment of absolute configuration when the molecules are chiral. A screen of 52 diverse compounds gave inclusion in co‐crystals for 88 % of all cases and a high‐resolution structure in 77 % of cases. Furthermore, starting from three milligrams of analyte, a combination of NMR spectroscopy and X‐ray crystallography produced a full structure in less than three days using an adamantane crystallization chaperone that encapsulates the analyte at room temperature.     

Plumeridoid C from the Amazonian traditional medicinal plant Himatanthus sucuuba

The stereochemistry of the iridoid plumeridoid C, C₁₅H₁₈O₇, was established by X‐ray single‐crystal structure analysis, giving (2′R,3R,4R,4aS,7aR)‐methyl 3‐hydroxy‐4′‐[(S)‐1‐hydroxyethyl]‐5′‐oxo‐3,4,4a,7a‐tetrahydro‐1H,5′H‐spiro[cyclopenta[c]pyran‐7,2′‐furan]‐4‐carboxylate. The absolute structure of the title compound was determined on the basis of the Flack x parameter and Bayesian statistics on Bijvoet differences. The hydrogen‐bond donor and acceptor functions of the two hydroxy groups are employed in the formation of O—H...O‐bonded helical chains.     

Acid‐Labile Amphiphilic PEO‐b‐PPO‐b‐PEO Copolymers: Degradable Poloxamer Analogs

Poly ((ethylene oxide)‐b‐(propylene oxide)‐b‐(ethylene oxide)) triblock copolymers commonly known as poloxamers or Pluronics constitute an important class of nonionic, biocompatible surfactants. Here, a method is reported to incorporate two acid‐labile acetal moieties in the backbone of poloxamers to generate acid‐cleavable nonionic surfactants. Poly(propylene oxide) is functionalized by means of an acetate‐protected vinyl ether to introduce acetal units. Three cleavable PEO‐PPO‐PEO triblock copolymers (M_n,total = 6600, 8000, 9150 g·mol⁻¹; M_n,PEO = 2200, 3600, 4750 g·mol⁻¹) have been synthesized using anionic ring‐opening polymerization. The amphiphilic copolymers exhibit narrow molecular weight distributions (Ð = 1.06–1.08). Surface tension measurements reveal surface‐active behavior in aqueous solution comparable to established noncleavable poloxamers. Complete hydrolysis of the labile junctions after acidic treatment is verified by size exclusion chromatography. The block copolymers have been employed as surfactants in a miniemulsion polymerization to generate polystyrene (PS) nanoparticles with mean diameters of ≈200 nm and narrow size distribution, as determined by dynamic light scattering and scanning electron microscopy. Acid‐triggered precipitation facilitates removal of surfactant fragments from the nanoparticles, which simplifies purification and enables nanoparticle precipitation “on demand.”

     

ansa-Metallocene derivatives XXXIII. 2-Dimethylamino-substituted bis-indenyl zirconium dichloride complexes with and without a dimethylsilyl bridge: syntheses, crystal structures and properties in propene polymerization catalysis

Bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (2-(CH₃)₂N-C₉H₆)₂ZrCl₂, and dimethylsilyl-bridged bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (CH₃)₂Si(2-(CH₃)₂N-C₉H₅)₂ZrCl₂, were prepared by reaction of the corresponding ligand lithium salts with ZrCl₄ in toluene. Diffractometric structure determinations reveal C₂-symmetric complex geometries for both complexes. An increased electron density at the Zr center of the dimethylamino-substituted complexes is indicated by reduction potentials which are 0.3–0.4 V more negative than those of their unsubstituted analogs. When activated with methyl aluminoxane in toluene solution, (CH₃)₂Si(2-(CH₃)₂N-C₉H₅)₂ZrCl₂ catalyzes the polymerization of propene to polymers with a microstructure comparable with that of polymers produced with other Me₂Si-bridged bis(indenyl)ZrCl₂ complexes, but with a substantially increased fraction of i-propyl end groups derived from alkyl exchange between Zr-polymer and Al---Me species.     

Non-constant curves of genus 2 with infinite pro-Galois covers

For every odd prime number p, we give examples of non-constant smooth families of curves of genus 2 over fields of characteristic p which have pro-Galois (pro-étale) covers of infinite degree with geometrically connected fibers. The Jacobians of the curves are isomorphic to products of elliptic curves.