Search results for "polymerization"
showing 10 items of 1689 documents
Achieving branched polyethylene waxes by aryliminocycloocta[b]pyridylnickel precatalysts: Synthesis, characterization, and ethylene polymerization
2017
Cycloocta[b]pyridin-10-one was prepared to form the corresponding imino derivatives, which then reacted with (DME)NiBr2 to form 10-aryliminocycloocta[b]pyridylnickel bromides (Ni1–Ni5). The new compounds were characterized by means of FT-IR spectroscopy as well as elemental analysis and the organic ligands were also analyzed by the NMR measurements. Furthermore, the molecular structure of a representative complex Ni3 was determined by the single crystal X-ray diffraction, indicating the distorted tetrahedral geometry around the nickel atom. Upon the activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et2AlCl), the title nickel complexes exhibited high activity in et…
Heterovalent ion replacement in bi7Ti4NbO21: Some new compounds and phase transitions
1996
Abstract Simultaneous heterovalent substitutions at two cationic sites of the bismuth mixed-layered compound Bi7Ti4NbO21 have been made. Two new compounds: Bi2Pb⅓Ti(4/3)Mo⅓O7 and Bi(4/3)PbTiMo⅔O7, were obtained and identified by X-ray diffraction analysis. A model of possible mixed layer structure is discussed. Ferroelectric phase transitions at 510°C and 550°C have been studied by dielectric measurements.
Hologram development by diffusion in a polymer glass
2003
Thick rigid polymer media with diffusive development of gratings are suitable for archive information storage, and especially for 3D holographic optical elements. Diffusion of unreacted molecules of photosensitive dye ensures postexposure growth of diffracted light, which can be followed either by secondary growth, or by some decay caused by displacement of chromophore groups photochemically attached to polymer chains (photoproduct). In a long run, extremely slow, though still finite, diffusion of macromolecules leads to destruction of a holographic grating. Not only the rate, but also the shape of postexposure kinetics noticeably depends on the choice of particular polymer, its degree of p…
First donor stabilized-phosphenium copper(I) complexes
2012
Abstract The preliminary studies of coordination properties of one donor stabilized-phosphenium adduct have been explored in copper chemistry. The preparation as well as the characterization of first examples of donor stabilized-phosphenium copper(I) complexes is reported in the paper. Thus, the direct addition of CuBr.SMe2 to an equivalent amount of cationic P‐ligands (L1+ or L2+)(PF6), with and , following by a crystallization in acetonitrile/Et2O led to first copper complexes [(L1,2+)CuBr2−] 1 and 3 and [(L1,2+)Cu+(NCMe)3+](PF6−)2 2 and 4 in a 1:1 ratio. However, when DMF/Et2O mixture was used as crystallization solvent, a stable bromo-bridged copper(I) dimer 5 [(L2+)CuBr(DMF)]2 was obta…
Reactions of pyridine-2-carbaldimines with chloro-bridged palladium(II) and platinum(II) 2-methylallyl dimers. Solution behaviour of the cationic com…
1987
Abstract The reactions of pyridine-2-carbaldimines, py-2- CHNR (R = C6H4OMe-p, Me), with allylic dimers [MCl(n3-2-MeC3H4)]2 give rise to stoichiometry, concentration, solvent and temperature dependent equilibria, in which the cationic complexes [M(n3- 2-MeC3H4)(py-2-CHNR)]+ and the anion [MCl2(n3- 2-MeC3H4)]- or Cl- are involved. In general, the ligand/dimer reaction (1/1 molar ratio) yields the ionic products [M(n3-2-MeC3H4)(py-2-CHNR)]- [MCl2(n3-2-MeC3H4)], which can be isolated as solids, whereas the same reaction in a 1/0.5 molar ratio yields the species [M(n3-2-MeC3H4 )(py-2-CH NR)] Cl, which can be studied only in solution, but are easily converted into [M(n3-2-MeC3H4)(py-2-CH NR…
Cycloaddition Reactions with Vinyl Heterocycles
1995
Publisher Summary The Diels-Alder reaction is one of the most common and elegant methods for the construction of six-membered rings. Although the number of Diels-Alder cycloadditions with open-chain and alicyclic dienes is very large, the number of examples with aromatic heterocyclic compounds is relatively small. The introduction of a vinyl group as a substituent onto a heterocycle increases the number of possible reactions. This new possibility, however attractive for synthetic purposes, is successful only with π-excessive five-membered heterocyclic derivatives with a few exceptions. The chapter discusses the reactions of vinyl heterocycles with carbodienophiles. The endocyclic and exo-en…
Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: A Robust Approach for Modeling Precipitation and Dispersion Kinetics
2012
A kinetic model is developed for the heterogeneous free-radical copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical CO 2. The model accounts for polymerization in both the dispersed (polymer-rich) phase and in the continuous (polymer-free) supercritical phase, for radical interphase transport, diffusion limitations, and chain-length-dependent termination in the polymer-rich phase. A parameter evaluation strategy is developed and detailed to estimate most of the kinetic parameters a priori while minimizing their evaluation by direct fitting. The resulting model predictions compare favorably with the experimental results of conversion and MWD at varying monomer fe…
Synthesis of hydrophilic polymers in supercritical carbon dioxide in the presence of a siloxane-based macromonomer surfactant: Heterogeneous polymeri…
2003
Batch free radical polymerization of 1-vinyl-2-pyrrolidone (VP) in super- critical carbon dioxide (scCO2) was studied in the presence of a reactive polysiloxane surfactant (PDMS-mMA). Phase behavior investigation showed that when the initial concentration of the surface active macromonomer was higher than 2.5% w/w with respect to the monomer, the reaction mixture, in the absence of efficient stirring, was initially opaque to the visible light, and it slowly turned to an orange tint. Polymeriza- tion experiments carried out with surfactant concentration higher than the aforemen- tioned value proceeded with a fast kinetics, and led to the formation of spherical nanoparticles with almost quant…
Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide stabilized with poly(ethylene glycol)-b-perfluoroalkyl compounds
2004
Abstract In this work selected components of an easily synthesible class of poly(ethylene glycol)-perfluoroalkyl block compounds were tested as stabilizers for the dispersion polymerization of methyl methacrylate in scCO 2 . As already observed in the case of different block surfactants the anchor soluble balance (ASB) of the stabilizer is the crucial parameter affecting the efficacy of the stabilization and the kinetics of the polymerization process. When stabilizers with appropriate ASB were used, high molecular weight poly(methyl methacrylate) was synthesized under the form of microspherical polymer particles with yields ranging up to 80%. In these experiments the occurrence of a gel-eff…
Dispersion Polymerization of Vinylidene Fluoride in Supercritical Carbon Dioxide
2006
The dispersion polymerization of vinylidene fluoride in supercritical carbon dioxide is investigated using two ammonium carboxylate perfluoropolyether stabilizers of different molecular weights. Under suitable operating conditions a polymer made of well-dispersed spherical particles has been obtained up to relatively high conversion. The experimental data of polymerization rate and molecular weight distribution are in good agreement with the predictions of a model previously developed. Such an agreement supports the conclusion that the polymerization kinetics is dominated by the interphase transport of the active radicals between the continuous phase and the polymer particles.