Kinetic Modeling as a Tool to Understand and Improve the Nitroxide Mediated Polymerization of Styrene

Kinetic modeling is used to obtain insight in the complex interplay between reaction rates and obtained polymer properties in the SG1 and the TEMPO mediated bulk polymerization of styrene at 396 K. The increase of the viscosity during NMP is accounted for. At higher targeted chain lengths, chain transfer to dimer and transfer from nitroxide to dimer are shown to cause the experimentally observed reduced control over the average polymer properties and to result in a clear fronting of the polymer chain length distribution. The potential of kinetic modeling to design tailor‐made synthesis strategies is illustrated. Simulations indicate that careful control of the polymerization conditions allows to obtain an important improvement of the polymer properties. The approach is also applicable for NMP mediated by other alkoxyamines/nitroxides and allows to expand the application range of NMP for styrene polymerization in particular to synthesize complex polymer architectures by assembly of functionalized polymers.

     

The development of polyamide 6.6 nanofibres with a pH-sensitive function by electrospinning

The development of a pH-sensitive nanofibrous sensor could contribute to interesting applications thanks to the combination of the pH-sensitive functionality and the unique characteristics of nanofibres. The effect of the addition of pH-sensitive dyes to the polymer solution is however unknown. Moreover also the halochromic behaviour of the resulting nonwovens can be influenced by this incorporation. Therefore, we studied the production of halochromic nano nonwovens by adding various pH-indicator dyes to a polyamide 6.6 polymer solution prior to electrospinning. Next, the halochromism of two selected dyes (Bromocresol Purple and Brilliant Yellow) was investigated as case studies. Our results show that the pH-indicator addition has no influence on the average fibre diameter. Poorly dissolved dyes cause however instabilities in the process as seen by the droplet formation. The investigated nanofibrous structures showed a clear colour change with a change in pH. This halochromic behaviour was however different from the behaviour of the dye in solution due to dye-fibre interactions. Generally it can be concluded that a nanofibrous pH-sensor can be developed by electrospinning with incorporated pH-indicator dyes.     

An ab initio molecular orbital study of the deprotonation of amines

The geometries of the amines NH₂X and amido anions NHX^?, where X = H, CH₃, NH₂, OH, F, C₂H, CHO, and CN have been optimized using ab initio molecular orbital calculations with a 4-31G basis set. The profiles to rotation about the N? X bonds in CH₃NH^?, NH₂NH^?, and HONH^? are very similar to those for the isoprotic and isoelectronic neutral compounds CH₃OH, NH₂OH, and HOOH. The amines with unsaturated bonds adjacent to the nitrogen atoms undergo considerable skeletal rearrangement on deprotonation such that most of the negative charge of the anion is on the substituent. The computed order of acidity for the amines NH₂X is X = CN > HCO > F ≈ C₂H > OH > NH₂ > CH₃ > H and for the reaction NHX^? + H⁺ → NH₂X the computed energies vary over the range 373–438 kcal/mol.     

Magnetic carbon nanotubes: synthesis by a simple solvothermal process and application in magnetic targeted drug delivery system

A poly(vinyl chloride) (PVC) main chain was grafted with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) containing a quaternary amine group using atom transfer radical polymerization. The successful synthesis of a PVC-g-PDMAEMA graft copolymer was confirmed by Fourier transform infrared, nuclear magnetic resonance, thermogravimetric analysis, and transmission electron microscopy. The PVC-g-PDMAEMA graft copolymer was used as a structure-directing agent (SDA) for the fabrication of a mesoporous thin film containing a titanium dioxide (TiO₂) layer. To control the porosity of the resultant inorganic layer, the ratio of SDA to TTIP as well as the concentration of the sol?Cgel was varied. The structure and porosity of the mesoporous film were characterized by XRD and SEM analysis. The mesoporous TiO₂ film fabricated on the FTO surface was used as a photoanode for the dye-sensitized solar cell (DSSC). DSSC performance was the greatest when using TiO₂ film with a higher porosity and lower interfacial resistance. The highest energy conversion efficiency reached 3.2?% at 100?mW/cm², which was one of the highest reported values for a quasi-solid-state DSSC with 600-nm-thick TiO₂ film.     

Stochastic utility-efficient programming of organic dairy farms

Opportunities to make sequential decisions and adjust activities as a season progresses and more information becomes available characterise the farm management process. In this paper, we present a discrete stochastic two-stage utility-efficient programming model of organic dairy farms, which includes risk aversion in the decision maker’s objective function as well as both embedded risk (stochastic programming with recourse) and non-embedded risk (stochastic programming without recourse). Historical farm accountancy data and subjective judgements were combined to assess the nature of the uncertainty that affects the possible consequences of the decisions. The programming model was used within a stochastic dominance framework to examine optimal strategies in organic dairy systems in Norway.     

Novel positive‐working and aqueous‐base‐developable photosensitive poly(imide benzoxazole) precursor

A novel positive‐working and aqueous‐base‐developable photosensitive poly(imide benzoxazole) precursor based on a poly(amic acid hydroxyamide) bearing phenolic hydroxyl groups and carboxylic acid groups, a diazonaphthoquinone (DNQ) photosensitive compound, and a solvent was developed. Poly(amic acid hydroxyamide) was prepared through the polymerization of 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane, trimellitic anhydride chloride, and 4,4′‐oxydibenzoyl chloride. Subsequently, the thermal cyclization of the poly(amic acid hydroxyamide) precursor at 350 °C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.17 dL/g. The cyclized poly(imide benzoxazole) showed a high glass‐transition temperature of 372 °C and 5% weight loss temperatures of 535 °C in nitrogen and 509 °C in air. The structures of the precursor polymer and the fully cyclized polymer were characterized with Fourier transform infrared and ¹H NMR. The photosensitive polyimide precursor containing 25 wt % DNQ photoactive compound showed a sensitivity of 256 mJ/cm² and a contrast of 1.14 in a 3‐μm film with a 0.6 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 5 μm was obtained from this composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5990–5998, 2004     

Synthesis and properties of novel electrophosphorescent polymers from quinoline‐ and pyridine‐end‐capped polyfluorenes with rhenium(I) chromophores

Novel electrophosphorescent polymers were prepared from quinoline‐ and pyridine‐end‐capped polyfluorenes reacted with 4,4′‐dimethyl‐2,2′‐bipyridyl (tricarbonyl)rhenium(I) chloride. Fourier transform infrared and photoluminescence spectroscopy confirmed that the rhenium complex was successfully incorporated into the polymer backbones. The energy transfer could be reached by an efficient intramolecular process. The emission contributions of the polyfluorene and organic complex were found from the electroluminescence spectra. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1492–1498, 2007     

Catalytic,Cascade Ring‐Opening Benzannulations of 2,3‐Dihydrofuran O,O‐ and N,O‐Acetals

An Al(OTf)₃‐catalyzed intramolecular cascade ring‐opening benzannulation of 2,3‐dihydrofuran O,O‐ and N,O‐acetals is described. The cascade sequence involves the dihydrofuran ring‐opening by acetal hydrolysis, an intramolecular Prins‐type cyclization, and aromatization to generate an array of benzo‐fused (hetero)aromatic systems in up to 95 % yield. This method represents the first example of dihydrofuran acetal usage in benzannulation reactions. The approach provides excellent regiocontrol based on the choice of alkenes used to form the requisite dihydrofuran acetals.