The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
Anuradha Varshney - One of the best experts on this subject based on the ideXlab platform.
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Free‐radical Polymerization of styrene with p‐nitrobenzyl triphenyl phosphonium ylide as an initiator
Journal of Polymer Science Part A: Polymer Chemistry, 2005Co-Authors: Kiran Prajapati, Anuradha VarshneyAbstract:The free-radical Polymerization of styrene with p-nitrobenzyl triphenyl phosphonium ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a Syndiotactic Polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight-average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the ylide and the free-radical mode of Polymerization. Differential scanning calorimetry studies showed the glass-transition temperature of the Polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005
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free radical Polymerization of styrene with p nitrobenzyl triphenyl phosphonium ylide as an initiator
Journal of Polymer Science Part A, 2005Co-Authors: Kiran Prajapati, Anuradha VarshneyAbstract:The free-radical Polymerization of styrene with p-nitrobenzyl triphenyl phosphonium ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a Syndiotactic Polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight-average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the ylide and the free-radical mode of Polymerization. Differential scanning calorimetry studies showed the glass-transition temperature of the Polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005
Kiran Prajapati - One of the best experts on this subject based on the ideXlab platform.
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Free‐radical Polymerization of styrene with p‐nitrobenzyl triphenyl phosphonium ylide as an initiator
Journal of Polymer Science Part A: Polymer Chemistry, 2005Co-Authors: Kiran Prajapati, Anuradha VarshneyAbstract:The free-radical Polymerization of styrene with p-nitrobenzyl triphenyl phosphonium ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a Syndiotactic Polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight-average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the ylide and the free-radical mode of Polymerization. Differential scanning calorimetry studies showed the glass-transition temperature of the Polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005
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free radical Polymerization of styrene with p nitrobenzyl triphenyl phosphonium ylide as an initiator
Journal of Polymer Science Part A, 2005Co-Authors: Kiran Prajapati, Anuradha VarshneyAbstract:The free-radical Polymerization of styrene with p-nitrobenzyl triphenyl phosphonium ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a Syndiotactic Polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight-average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the ylide and the free-radical mode of Polymerization. Differential scanning calorimetry studies showed the glass-transition temperature of the Polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005
Lido Porri - One of the best experts on this subject based on the ideXlab platform.
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Polymerization of 4-methyl -1,3-pentad iene with MAO/Ti(OnBu)4. The influence of preparation/ageing temperature upon the stereospecificity of the catalyst
Polymer, 1997Co-Authors: Giovanni Ricci, Lido PorriAbstract:Abstract 4-Methyl-l,3-pentadiene has been Polymerized with the system Ti(OnBu) 4 /MAO at different temperatures in the range +20°C to −78°C, using aged and unaged catalysts. The Polymers obtained have a 1,2 Syndiotactic or a mixed 1,2 Syndiotactic/1,2 isotactic structure, depending on the Polymerization temperature and on the temperature and time of ageing of the catalyst. The percentage of Syndiotactic Polymer depends on the Polymerization temperature, but also on the time and temperature of ageing of the catalysts. The formation of isotactic Polymer together with Syndiotactic Polymer has been attributed to the presence of two different active centres. The centres that produce the Syndiotactic Polymer increase with the time and temperature of ageing.
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Polymerization of (Z)-1,3-pentadiene with CpTiCl3/MAO. Effect of temperature on Polymer structure and mechanistic implications
Macromolecules, 1994Co-Authors: Giovanni Ricci, Salvatore Italia, Lido PorriAbstract:A change of stereospecificity with temperature has been observed in the Polymerization of (Z)-1,3-pentadiene with the homogeneous system CpTiCl 3 /MAO: a cis-1,4-isotactic Polymer is obtained at +20°C and a 1,2-Syndiotactic Polymer at -20°C
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Polymerization of styrene with the titanium trichloride/methylaluminoxane catalyst system
Macromolecules, 1993Co-Authors: Marcos L. Dias, Antonino Giarrusso, Lido PorriAbstract:The Polymerization of styrene with catalysts derived from aluminium-activated TiCl 3 , from hydrogen-activated TiCl 3 and from the soluble complex TiCl 3 .3THF was investigated. It was found that crystalline TiCl 3 gives on reaction with methylaluminoxane (MAO) in toluene two types of catalyst systems: a soluble one, which Polymerizes styrene to Syndiotactic Polymer, and an insoluble one, which Polymerizes styrene to isotactic one. A soluble catalyst for the Syndiotactic Polymerization of styrene can be obtained from TiCl 3 .THF and MAO.
Yoshio Okamoto - One of the best experts on this subject based on the ideXlab platform.
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Stereocontrol in Radical Polymerization of N,N-Dimethylacrylamide and N,N-Diphenylacrylamide and Thermal Properties of Syndiotactic Poly(methyl acrylate)s Derived from the Obtained Polymers
Polymer Journal, 2000Co-Authors: Weihong Liu, Tamaki Nakano, Yoshio OkamotoAbstract:Free-radical Polymerization of N,N -dimethylacrylamide (DMAA) and N,N -dephenylacrylamide (DPAA) were carried out under various conditions. DMAA gave an isotactic-rich Polymer in most cases, whereas DPAA gave a Syndiotactic Polymer. The Polymerization stereochemistry was also affected by reaction solvents including toluene, tetrahydrofuran, and fluoroalcohols. It is notable that the stereochemistry of the Polymerization depended on monomer concentration: a lower monomer concentration led to a higher isotacticity for DMAA Polymerization and a higher Syndiotacticity for DPAA Polymerization. This effect was explained by assuming that there exist two types of growing radicals having different stereoselectivities. By optimizing the aforementioned reaction conditions, poly(DMAA) with dial isotacticity ( m ) of 77% (Polymerization in toluene at −78°C at [M]_0=0.1M) and poly(DPAA) with diad Syndiotacticity ( r ) of 93% (Polymerization in THF at -98°C at [M]_0=0.22M) were obtained. Stereoregular poly(methyl acrylate)s were derived from the poly(DPAA)s. Thermal property of the poly(methyl acrylate)s with different tacticities was studied by DSC.
Giovanni Ricci - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Structure of Syndiotactic Poly(3-methyl-1-butene): A Case of 3/1 Helical Conformation for Syndiotactic Polymers
2018Co-Authors: Claudio De Rosa, Anna Malafronte, Miriam Scoti, Finizia Auriemma, Ivana Pierro, Giuseppe Leone, Giovanni RicciAbstract:Syndiotactic poly(3-methyl-1-butene) (sP3MB) has been obtained for the first time by hydrogenation of 3,4-poly(isoprene), which in turn has been synthesized with the catalyst FeCl2(2,2′-bipyridine)2 activated with methylaluminoxane. The synthesized sample of sP3MB is amorphous but crystallizes by stretching and annealing of the oriented amorphous phase at 60–70 °C. The diffraction image of the annealed fibers shows only three equatorial reflections and a few weak reflections distributed on three nonequatorial layer lines. From these data a model of the conformation of the chains of sP3MB is proposed. The chains of sP3MB assume in the crystalline phase a 3/1 helical conformation, providing the first example of a Syndiotactic Polymer with 3-fold helical chains. A high degree of disorder is present in the crystals so that the structure can be described by an arrangement of parallel conformationally ordered 3/1 helical chains and disorder in the lateral correlations between the chains
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Polymerization of 1 3 dienes with iron complexes based catalysts influence of the ligand on catalyst activity and stereospecificity
Journal of Molecular Catalysis A-chemical, 2003Co-Authors: Giovanni Ricci, Daniele Morganti, Anna Sommazzi, Roberto Santi, Francesco MasiAbstract:Abstract Various iron dichloride complexes with aliphatic and aromatic bidentate amine ligands have been synthesized and used, in combination with aluminium-compounds (AlR3 or methylaluminoxane (MAO)), for the Polymerization of 1,3-dienes. Catalyst activity, chemo- and stereoselectivity are strongly influenced by the type of ligand; systems based on iron complexes with aromatic bidentate amines (e.g. bypiridine or phenantroline), in particular, exhibit an extremely high activity, giving from butadiene a 1,2-Syndiotactic Polymer. These systems are also able to Polymerize substituted butadienes (e.g. isoprene, (E)-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene) giving Polymers with different structure from the different monomers; these results have permitted to confirm some aspects of the Polymerization mechanism previously proposed.
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Polymerization of 4-methyl -1,3-pentad iene with MAO/Ti(OnBu)4. The influence of preparation/ageing temperature upon the stereospecificity of the catalyst
Polymer, 1997Co-Authors: Giovanni Ricci, Lido PorriAbstract:Abstract 4-Methyl-l,3-pentadiene has been Polymerized with the system Ti(OnBu) 4 /MAO at different temperatures in the range +20°C to −78°C, using aged and unaged catalysts. The Polymers obtained have a 1,2 Syndiotactic or a mixed 1,2 Syndiotactic/1,2 isotactic structure, depending on the Polymerization temperature and on the temperature and time of ageing of the catalyst. The percentage of Syndiotactic Polymer depends on the Polymerization temperature, but also on the time and temperature of ageing of the catalysts. The formation of isotactic Polymer together with Syndiotactic Polymer has been attributed to the presence of two different active centres. The centres that produce the Syndiotactic Polymer increase with the time and temperature of ageing.
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Polymerization of (Z)-1,3-pentadiene with CpTiCl3/MAO. Effect of temperature on Polymer structure and mechanistic implications
Macromolecules, 1994Co-Authors: Giovanni Ricci, Salvatore Italia, Lido PorriAbstract:A change of stereospecificity with temperature has been observed in the Polymerization of (Z)-1,3-pentadiene with the homogeneous system CpTiCl 3 /MAO: a cis-1,4-isotactic Polymer is obtained at +20°C and a 1,2-Syndiotactic Polymer at -20°C
