Versatile Organometallic Initiators for the Living Polymerization of Isocyanates

Shashoua and Sweeney first demonstrated that isocyanates could by polymerized via an anionic mechanism to form high molecular weight materials. We have sought to eliminate the problems associated with the anionic procedure by developing transition metal complexes which are capable of catalyzing the living polymerization of isocyanates. Recently, we reported the living polymerization of alkyl isocyanates using TiCl₃OCH₂CF₃, I. Using I, polyisocyanates with controlled molecular weights and narrow polydispersities can be obtained at room temperature. ε⁵-CpTiCl₂N(CH₃)₂ (Cp = cyclopentadienyl), III, is also an excellent catalyst for the polymerization of isocyanates, and in terms of ease of handling and purification and tolerance toward monomer functionality, superior to I. In order to prepare triblock copolymers containing amorphous segments sandwiched between two isocyanate segments, we have prepared bimetallic initiators comprised of titanium alkoxides con- nected by flexible linkers. These linkers may be a small molecule (1,4- dihydroxycyclohexane, V) or a polymer (polydimethylsiloxane, PDMS, VI). Complexes V and VI can be used to initiate the living polymerization of isocyanates to yield polymers possessing central cyclohexyl bends (ldquo;broken worms rdquo;) or PDMS segments (triblock copolymers), respectively. Finally, cyclopolymerizations of 1,2-diisocyanates using these or- ganometallic initiators are reported.     

Adamantyl Side Chains as Anti-Aggregating Moieties in Dyes for Dye-Sensitized Solar Cells

Designing and evaluating novel dye concepts is crucial for the development of the field of dye-sensitized solar cells (DSSCs). In our recent report, the novel concept of tethering the anti-aggregation additive chenodeoxycholic acid (CDCA) to dyes for DSSC was introduced. Based on the performance improvements seen for this modification, the aim of this study is to see if a simplified anti-aggregation unit could achieve similar results. The following study reports the synthesis and photovoltaic characterization of two novel dyes decorated with the steric ethyladamantyl moiety on the π-spacer, and on the triarylamine donor. This modification is demonstrated to be successful in increasing the photovoltages in devices employing copper-based electrolytes compared to the non-modified reference dye. The best photovoltaic performance is achieved by a device prepared with the adamantyl decorated donor dye and CDCA, this device achieves a power conversion efficiency of 6.1 % (Short-circuit current=8.3 mA cm⁻², Open-circuit voltage=1054 mV, Fill factor=0.69). The improved photovoltaic performance seen for the adamantyl decorated donor demonstrate the potential of ethyladamantyl side chains as a tool to ensure surface protection of TiO₂.     

On the role of organic adlayers in the anomalous water sorptivity of Lépine limestone

Sorptivity data are reported for the capillary absorption of water, ethanol, propan-2-ol, and n-heptane by the calcitic limestone Lépine (Lavoux à grain). The data confirm that the water sorptivity is anomalously low, an indication of partial wetting by water. Results are expressed in terms of a wetting index. The water sorptivity increases after heat treatment and chemical oxidation by hydrogen peroxide bleaching, while the sorptivity with organic liquids is unchanged. These treatments, therefore, increase the water wetting index. The results provide strong evidence that the presence of a natural organic adlayer is responsible for the anomalously low water sorptivity of this particular limestone. This natural water repellency effect may be exploited in developing chemical treatments to modify the water transport properties of stone.     

Improved branching ratio measurement for the decay K(0)(L) --> &mgr;(+)&mgr;(-)

We report results from Experiment 871, performed at the BNL AGS, of a measurement of the branching ratio K(0)(L)-->&mgr;(+)&mgr;(-) with respect to the CP-violating mode K(0)(L)-->pi(+)pi(-). This experiment detected over 6200 candidate &mgr;(+)&mgr;(-) events, a factor of 6 more than that seen in all previous measurements combined. The resulting branching ratio gamma(K(0)(L)-->&mgr;(+)&mgr;(-))/gamma(K(0)(L)-->pi(+)pi(-)) = (3. 474+/-0.057)x10(-6) leads to a branching fraction B(K(0)(L)-->&mgr;(+)&mgr;(-)) = (7.18+/-0.17)x10(-9), which is consistent with the current world average, and reduces the uncertainty in this decay mode by a factor of 3.     

Die Methoden zur direkten Messung des osmotischen Drucks

Ohne Zusammenfassung     

1H,13C and 19F NMR data of N‐substituted 6‐(4‐methoxyphenyl)‐7H‐pyrrolo[2,3‐d]pyrimidin‐4‐amines in DMSO‐d6

Chemical shift assignment of seven N‐substituted 6‐(4‐methoxyphenyl)‐7H‐pyrrolo[2, 3‐d]pyrimidin‐4‐amines, six of which are fluorinated, have been performed based on ¹H, ¹³C, ¹⁹F, and 2D COSY, HMBC and HSQC experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Clean-up of some organochlorine and pyrethroid insecticides by automated solid-phase extraction cartridges coupled to capillary GC-ECD

The ASPEC (Automatic Sample Preparation with Extraction Columns) system has been coupled on-line to capillary GC-ECD by means of a loop-type interface equipped with a solvent vapour exit. Both ASPEC and GC conditions have been optimized leading to an effective clean-up of the extracts analyzed. By means of solid-phase extraction cartridges filled with silica, it has been possible to analyze concentrated surface water extracts for a group of 18 electron-capturing compounds present in the water at ppt levels. ASPEC-GC has also been applied to the determination of synthetic pyrethroids at ppt levels in surface water. The complete analytical procedure is greatly facilitated by automation and miniaturization. Miniaturization results in a considerable decrease in the sample volume required. The potential of the method for the analysis of other pesticides is estimated.