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Initiation Efficiency (initiation + efficiency)
Selected AbstractsMixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium- Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Xavier Sauvage Abstract Two new second generation ruthenium(II) dichloride-indenylidene complexes [RuCl2(9-isobutylphosphabicyclo[3.3.1]nonane)(NHC)(3-phenyl-1-indenylidene)], where NHC=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) or its unsaturated imidazol-2-ylidene analogue (IMes), were isolated in high yields upon heating a tetrahydrofuran (THF) solution of the diphosphane complex [RuCl2(isobutylphobane)2(3-phenyl-1-indenylidene)] with a two-fold excess of the corresponding imidazol(in)ium-2-carboxylate zwitterions. Both products were characterized by 1H, 13C, and 31P,NMR spectroscopy, and the molecular structure of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was determined by X-ray diffraction analysis. A close inspection of the packing structure revealed the presence of different types of intra- and intermolecular interactions that enhanced the global stability of the crystals, while low temperature NMR experiments showed the existence of two distinct rotational isomers due to the unsymmetrical nature of the phobane ligand. The catalytic activity of both compounds was assessed in olefin metathesis using benchmark ring-opening metathesis polymerization, ring-closing metathesis (RCM), and cross-metathesis reactions, and compared with those of related first and second generation ruthenium-benzylidene and indenylidene catalyst precursors. Kinetic studies confirmed the high thermal stability of the mixed isobutylphobane/N-heterocyclic carbene complexes, which suffered from a slow initiation efficiency compared to other catalytic systems based on the tricyclohexylphosphane ligand. However, the remarkable robustness of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was beneficial for performing the RCM of diethyl 2,2-bis(2-methylallyl)malonate. Monitoring the formation of the ruthenium-methylidene active species [RuCl2(isobutylphobane)(SIMes)(CH2)] derived from this precursor further demonstrated its ability to sustain long reaction times and high temperatures required to carry out the RCM of tetrasubstituted olefins. [source] Synthesis and characterization of hyperbranched-poly(siloxysilane)-based polymeric photoinitiatorsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006Qing-Fa Si Abstract Three UV-sensitive, hyperbranched-poly(siloxysilane)-based polymeric photoinitiators, bearing an alkyl phenone moiety linked to the surface of the hyperbranched polymer, were synthesized via the hydrosilylation of hyperbranched poly(siloxysilane) and modified UV-sensitive compounds. Hyperbranched poly(siloxysilane) was prepared via the polyhydrosilylation of the AB2 -type monomer methylvinyldichlorosilane. The chemical structures of the polymeric photoinitiators were characterized with 1H, 13C, and 29Si NMR, elemental analysis, Fourier transform infrared, differential scanning calorimetry, UV spectrophotometry, and thermogravimetric analysis. The UV-curing behaviors of the blends of the hyperbranched polymeric photoinitiators with UV-curable epoxy acrylate (EA) resin were determined by Fourier transform infrared, and the results showed that the initiation efficiency of the polymeric photoinitiators was excellent and that the thermostability of the EA/polymeric photoinitiator curing systems was higher than that of the EA/photoinitiators. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3261,3270, 2006 [source] Synthesis of homopolymers and multiblock copolymers by the living ring-opening metathesis polymerization of norbornenes containing acetyl-protected carbohydrates with well-defined ruthenium and molybdenum initiatorsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2004Yoshitaka Miyamoto Abstract The ring-opening metathesis polymerization (ROMP) of norbornenes containing acetyl-protected glucose [2,3,4,6-tetra- O -acetyl-glucos-1- O -yl 5-norbornene-2-carboxylate (1)] and maltose [2,3,6,2,,3,,4,,6,-hepta- O -acetyl-maltos-1- O -yl 5-norbornene-2-carboxylate (2)] was explored in the presence of Mo(N -2,6- iPr2C6H3)(CHCMe2Ph)(OtBu)2 (A), Ru(CHPh)(Cl)2(PCy3)2 (B; Cy = cyclohexyl), and Ru(CHPh)(Cl)2(IMesH2)(PCy3) (C; IMesH2 = 1,3-dimesityl-4,5-dihydromidazol-2-ylidene). The polymerizations promoted by B and A proceeded in a living fashion with exclusive initiation efficiency, and the resultant polymers possessed number-average molecular weights that were very close to those calculated on the basis of the monomer/initiator molar ratios and narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight < 1.18) in all cases. The observed catalytic activity of B was strongly dependent on both the initial monomer concentration and the solvent employed, whereas the polymerization initiated with A was completed efficiently even at low initial monomer concentrations. The polymerization with C also took place efficiently, and even the polymerization with 1000 equiv of 1 was completed within 2 h. First-order relationships between the propagation rates and the monomer concentrations were observed for all the polymerization runs, and the estimated rate constants at 25 °C increased in the following order: A > C > B. On the basis of these results, we concluded that ROMP with A was more suitable than ROMP with B or C for the efficient and precise preparation of polymers containing carbohydrates. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4248,4265, 2004 [source] Photopolymerization of 1,6-hexanedioldiacrylate initiated by three-component systems based on N -arylphthalimidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2004T. Brian Cavitt Abstract Three-component photoinitiators comprised of an N -arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron-deficient N -arylphthalimide resulted in a greater acrylate polymerization rate than an electron-rich N -arylphthalimide. Triplet energies of each N -arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N -arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron,proton transfer from an intermediate radical species to the N -arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009,4015, 2004 [source] Kinetic Study and New Applications of UV Radiation CuringMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2002Christian Decker Abstract Highly crosslinked polymers can be readily synthesized by photoinitiated polymerization of multifunctional monomers or functionalized polymers. The reaction can be followed in situ by real-time infrared (RT-IR) spectroscopy, a technique that records conversion versus time curves in photosensitive resins undergoing ultrafast polymerization upon UV exposure. For acrylate-based resins, UV-curing proceeds with long kinetic chains (7700 mol/radical) in spite of the high initiation rate. RT-IR spectroscopy proved very valuable in assessing the influence of various parameters, such as initiation efficiency, chemical structure of the telechelic oligomer, light intensity, inhibitory effect of oxygen, on polymerization kinetics. Interpenetrating polymer networks can be rapidly synthesized by means of UV irradiation of a mixture of difunctional acrylate and epoxy monomers in the presence of both radical and cationic-type photoinitiators. The same UV technology can be applied to crosslink solid polymers at ambient temperature, which bear different types of reactive groups (acrylate and vinyl double bonds, epoxy ring). UV radiation curing has been successfully used to produce within seconds weathering resistant protective coatings, high-resolution relief images, glass laminates and nanocomposites materials. Photoinitiated crosslinking polymerization. [source] | ||||||||||