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Kooji Mizunuma - One of the best experts on this subject based on the ideXlab platform.
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chain transfer reaction by trialkylaluminum air3 in the stereospecific polymerization of propylene with metallocene air3 ph3cb c6f5 4
Polymer, 1998Co-Authors: Naofumi Naga, Kooji MizunumaAbstract:Abstract Stereospecific polymerization of propylene was carried out with rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2) (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (rac-Me2Si(Ind)2ZrCl2) (2) and isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (i-Pr(Cp)(Flu)ZrCl2) (3) combined with trialkyl-aluminum (AIR3: R = C2H5, i-C4H9)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (4). In isospecific polymerization with 1 and 2, the molecular weight of Polypropylenes decreased with increase in the molar ratio of AlEt3 (Et = C2H5)/Zr, whereas, an effect of AliBu3 (iBu = i-C4H9) concentration on molecular weight was not observed. The microstructures of resulting Polypropylenes were studied by 13C n.m.r. and an increase in the molar ratio of ethyl end groups (derived from chain transfer to AlEt3) to n-propyl end groups (derived from β-hydrogen transfer) was observed with increase in the molar ratio of AlEt 3 Zr (1 and 2). The chain transfer reactions by both AlEt3 and AliBu3 were also detected in syndiospecific polymerization with 3. The molar ratio of alkyl (R) end groups (derived from chain transfer to AIR3) to n-propyl end groups was higher in the polypropylene obtained with AlEt3 than that obtained with AliBu3. The relative constants k trA k p (ktrA = rate constant of chain transfer to AIR3, kp = rate constant of propagation) were determined by kinetic study.
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Chain transfer reaction by trialkylaluminum (AIR3) in the stereospecific polymerization of propylene with metallocene — AIR3/Ph3CB(C6F5)4
Polymer, 1998Co-Authors: Naofumi Naga, Kooji MizunumaAbstract:Abstract Stereospecific polymerization of propylene was carried out with rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2) (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (rac-Me2Si(Ind)2ZrCl2) (2) and isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (i-Pr(Cp)(Flu)ZrCl2) (3) combined with trialkyl-aluminum (AIR3: R = C2H5, i-C4H9)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (4). In isospecific polymerization with 1 and 2, the molecular weight of Polypropylenes decreased with increase in the molar ratio of AlEt3 (Et = C2H5)/Zr, whereas, an effect of AliBu3 (iBu = i-C4H9) concentration on molecular weight was not observed. The microstructures of resulting Polypropylenes were studied by 13C n.m.r. and an increase in the molar ratio of ethyl end groups (derived from chain transfer to AlEt3) to n-propyl end groups (derived from β-hydrogen transfer) was observed with increase in the molar ratio of AlEt 3 Zr (1 and 2). The chain transfer reactions by both AlEt3 and AliBu3 were also detected in syndiospecific polymerization with 3. The molar ratio of alkyl (R) end groups (derived from chain transfer to AIR3) to n-propyl end groups was higher in the polypropylene obtained with AlEt3 than that obtained with AliBu3. The relative constants k trA k p (ktrA = rate constant of chain transfer to AIR3, kp = rate constant of propagation) were determined by kinetic study.
R D K Misra - One of the best experts on this subject based on the ideXlab platform.
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scratch deformation behavior of thermoplastic materials with significant differences in ductility
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: R S Hadal, R D K MisraAbstract:Abstract A comparative study of the scratch deformation behavior of neat ethylene–propylene copolymers and polypropylene with significant differences in ductility is made by combining morphological examination by electron microscopy and scratch deformation parameters by atomic force microscopy. Also, the deformation behavior during scratch tests is examined for their respective long and short chain polymers. The ability of polymeric materials to resist scratch deformation under identical scratch test conditions follows the sequence (from maximum resistance to minimum resistance): short chain polypropylene > long chain polypropylene > short chain ethylene–propylene > long chain ethylene–propylene. The scratch tracks in ethylene–propylene copolymers were characterized by a consecutive parabolic pattern containing voids, while Polypropylenes exhibited zig-zag periodic scratch tracks. The greater plastic flow in ethylene–propylene copolymers is encouraged by the high ductility of the copolymer and the ability to nucleate microvoids. The quasi-static periodic scratch tracks are a consequence of sequential accumulation and release of tangential force and represents the stick–slip process. The susceptibility to scratch deformation is discussed in terms of modulus, elastic recovery, scratch hardness, and entanglement density of polymeric materials. A higher effective entanglement density and percentage crystallinity of short chain polymers is helpful in enhancing scratch resistance as compared to their respective long chain polymers.
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the influence of loading rate and concurrent microstructural evolution in micrometric talc and wollastonite reinforced high isotactic polypropylene composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: R S Hadal, R D K MisraAbstract:The paper describes the response of neat high isotactic polypropylene (iPP) and talc (iPP-T) and wollastonite (iPP-W)-reinforced Polypropylenes to tensile loading rate and the evolution of microstructure during plastic deformation. Unreinforced and reinforced polypropylene materials exhibit significant sensitivity to tensile loading rate (strain rate) and the change in strain rate sensitivity index parameter with strain signifies a change in the micromechanism of plastic deformation and mode of fracture. Plastic deformation in neat high isotactic polypropylene is characterized by craze-tearing and brittle mode of fracture, while both talc- and wollastonite-reinforced Polypropylenes are characterized by wedge, ridge-tearing, fibrillation, and brittle fracture. The brittle fracture is associated with debonding of mineral particles from the polypropylene matrix. However, yield stress of all the three materials exhibit similar dependence to loading rate and similar activation volume that suggests similarity in the onset of plastic deformation process.
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effect of wollastonite and talc on the micromechanisms of tensile deformation in polypropylene composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: R S Hadal, Aravind Dasari, Juergen Rohrmann, R D K MisraAbstract:Abstract The work presented here describes the effect of wollastonite and talc on the micromechanisms of surface deformation and subsequent propagation into the bulk of low and high crystallinity Polypropylenes during tensile straining. The potential of high resolution electron microscopy is utilized to examine deformation processes, and develop deformation mechanism maps. While mineral-reinforced Polypropylenes exhibited an increase in tensile modulus, yield strength remained unaffected. Crystallization behavior indicated that the reinforcement minerals increase the rate of nucleation with consequent increase in percentage of bulk crystallinity. The reinforcement of polypropylene with wollastonite or talc alters the primary micromechanism of deformation from deformation bands/crazing in neat Polypropylenes to wedge/ridge tearing in mineral-reinforced low crystallinity polypropylene composites. However, wedges were absent in high crystallinity polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing–tearing and brittle deformation are fracture modes for neat Polypropylenes.
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the role of micrometric wollastonite particles on stress whitening behavior of polypropylene composites
Acta Materialia, 2004Co-Authors: Aravind Dasari, R D K MisraAbstract:The micromechanism and susceptibility to stress whitening during tensile straining of micrometric wollastonite mineral-reinforced Polypropylenes is studied by electron microscopy and compared with unreinforced neat Polypropylenes. Mineral-reinforced polypropylene composite exhibit significantly reduced susceptibility to stress whitening, and are characterized by lower gray level in the plastically deformed stress whitened zone. This behavior is attributed to the effective reinforcement of polypropylene by wollastonite that acts in concert increasing the tensile modulus of the composite and restricts plastic deformation of the matrix. The increase in tensile modulus is explained in terms of a three-phase model involving matrix, particle, and interface zone. Furthermore, isothermal crystallization indicated that the reinforcement mineral increases the rate of nucleation with consequent increase in % bulk crystallinity. The reinforcement of polypropylene alters the primary micromechanism of stress whitening from deformation bands/crazing in neat Polypropylenes to wedge/ridge-tearing in mineral-reinforced polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing-tearing and brittle deformation are fracture modes for neat polypropylene.
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on the scratch deformation of micrometric wollastonite reinforced polypropylene composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: Aravind Dasari, Juergen Rohrmann, R D K MisraAbstract:Scratch deformation characteristics of neat and wollastonite-containing Polypropylenes under identical test conditions are examined by electron microscopy and atomic force microscopy techniques. The study indicates that the severity of plastic deformation during scratch deformation in filled Polypropylenes is a strong function of the debonding/detachment of wollastonite mineral particles from the polypropylene matrix. Scratch resistance is evaluated in terms of scratch hardness, scratch depth, average scratch roughness, thickness and density of the scratch tracks. Atomic force microscopy suggests the presence of a localized region surrounding the reinforcement particle that is characterized by enhanced crystal nucleation in which the local chain conformation and kinetics are likely to be different from regions that are a significant distance away from the mineral particle.
Douglas R Lloyd - One of the best experts on this subject based on the ideXlab platform.
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effect of the polypropylene type on polymer diluent phase diagrams and membrane structure in membranes formed via the tips process part ii syndiotactic and isotactic Polypropylenes produced using metallocene catalysts
Journal of Membrane Science, 2005Co-Authors: Wilfredo Yave, Raul Quijada, Daniel Serafini, Douglas R LloydAbstract:Abstract Syndiotactic polypropylene (sPP) and isotactic polypropylene (iPP) were used to investigate the effect of the polypropylene microstructure (tacticity) on phase diagrams for PP–diphenyl ether systems and the morphology of membranes made from these systems. The syndiotactic and isotactic Polypropylenes were both produced via metallocene catalysts and had similar average molecular weights. It was found experimentally that polypropylene microstructure affects the location of the binodal curve and the morphology of membranes produced via the thermally induced phase separation (TIPS) process. The influence on the binodal curve was attributed to stereochemistry effects, chain rigidity, and local chain packing. In isothermal experiments, droplet size was similar for the two types of PP, while in non-isothermal experiments, the sPP sample yielded larger droplets than the iPP sample. These results were attributed mainly to viscous effects and to differences in the growth period (resulting from a shift in the cloud point and dynamic crystallization curves). The final morphology of the sPP membrane was related to polymer chain flexibility and to shrinkage of the sample during diphenyl ether extraction and sample drying.
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Effect of the polypropylene type on polymer–diluent phase diagrams and membrane structure in membranes formed via the TIPS process: Part II. Syndiotactic and isotactic Polypropylenes produced using metallocene catalysts
Journal of Membrane Science, 2005Co-Authors: Wilfredo Yave, Raul Quijada, Daniel Serafini, Douglas R LloydAbstract:Abstract Syndiotactic polypropylene (sPP) and isotactic polypropylene (iPP) were used to investigate the effect of the polypropylene microstructure (tacticity) on phase diagrams for PP–diphenyl ether systems and the morphology of membranes made from these systems. The syndiotactic and isotactic Polypropylenes were both produced via metallocene catalysts and had similar average molecular weights. It was found experimentally that polypropylene microstructure affects the location of the binodal curve and the morphology of membranes produced via the thermally induced phase separation (TIPS) process. The influence on the binodal curve was attributed to stereochemistry effects, chain rigidity, and local chain packing. In isothermal experiments, droplet size was similar for the two types of PP, while in non-isothermal experiments, the sPP sample yielded larger droplets than the iPP sample. These results were attributed mainly to viscous effects and to differences in the growth period (resulting from a shift in the cloud point and dynamic crystallization curves). The final morphology of the sPP membrane was related to polymer chain flexibility and to shrinkage of the sample during diphenyl ether extraction and sample drying.
Gerhard Fink - One of the best experts on this subject based on the ideXlab platform.
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Stereospecific propylene polymerization using half-sandwich metallocene/MAO systems : a mechanistic insight
Journal of Molecular Catalysis A-chemical, 2000Co-Authors: Ralph Kleinschmidt, Yolanda Griebenow, Gerhard FinkAbstract:The propylene polymerizations with different half-sandwich metallocene complexes of the general formula, Me2Si[Me4CpNR]TiCl2, result in the formation of polymers with increased isotacticity as compared to atactic polypropylene. This was observed if a sterically demanding aromatic system at the amido-ligand coordinates with the polymerization active metal center. In this case, the metal center is partly shielded and the steric demand of the ligand is similar to an ansa-metallocene. The monomer partly coordinates stereospecifically at the metal center. Additionally, the solvent polarity has a great influence on the microstructure of the produced polymers. Using the complex Me2Si[Me4CpNCHCH3naphthyl]TiCl2 in toluene, ortho-dichlorobenzene and hexane Polypropylenes of similar microstructures were formed (mmmm≈45%) whereas in methylene chloride as solvent, the isotacticity of the polypropylene was decreased by 50%.
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stereospecific propylene polymerization using half sandwich metallocene mao systems a mechanistic insight
Journal of Molecular Catalysis A-chemical, 2000Co-Authors: Ralph Kleinschmidt, Yolanda Griebenow, Gerhard FinkAbstract:The propylene polymerizations with different half-sandwich metallocene complexes of the general formula, Me2Si[Me4CpNR]TiCl2, result in the formation of polymers with increased isotacticity as compared to atactic polypropylene. This was observed if a sterically demanding aromatic system at the amido-ligand coordinates with the polymerization active metal center. In this case, the metal center is partly shielded and the steric demand of the ligand is similar to an ansa-metallocene. The monomer partly coordinates stereospecifically at the metal center. Additionally, the solvent polarity has a great influence on the microstructure of the produced polymers. Using the complex Me2Si[Me4CpNCHCH3naphthyl]TiCl2 in toluene, ortho-dichlorobenzene and hexane Polypropylenes of similar microstructures were formed (mmmm≈45%) whereas in methylene chloride as solvent, the isotacticity of the polypropylene was decreased by 50%.
Naofumi Naga - One of the best experts on this subject based on the ideXlab platform.
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chain transfer reaction by trialkylaluminum air3 in the stereospecific polymerization of propylene with metallocene air3 ph3cb c6f5 4
Polymer, 1998Co-Authors: Naofumi Naga, Kooji MizunumaAbstract:Abstract Stereospecific polymerization of propylene was carried out with rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2) (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (rac-Me2Si(Ind)2ZrCl2) (2) and isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (i-Pr(Cp)(Flu)ZrCl2) (3) combined with trialkyl-aluminum (AIR3: R = C2H5, i-C4H9)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (4). In isospecific polymerization with 1 and 2, the molecular weight of Polypropylenes decreased with increase in the molar ratio of AlEt3 (Et = C2H5)/Zr, whereas, an effect of AliBu3 (iBu = i-C4H9) concentration on molecular weight was not observed. The microstructures of resulting Polypropylenes were studied by 13C n.m.r. and an increase in the molar ratio of ethyl end groups (derived from chain transfer to AlEt3) to n-propyl end groups (derived from β-hydrogen transfer) was observed with increase in the molar ratio of AlEt 3 Zr (1 and 2). The chain transfer reactions by both AlEt3 and AliBu3 were also detected in syndiospecific polymerization with 3. The molar ratio of alkyl (R) end groups (derived from chain transfer to AIR3) to n-propyl end groups was higher in the polypropylene obtained with AlEt3 than that obtained with AliBu3. The relative constants k trA k p (ktrA = rate constant of chain transfer to AIR3, kp = rate constant of propagation) were determined by kinetic study.
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Chain transfer reaction by trialkylaluminum (AIR3) in the stereospecific polymerization of propylene with metallocene — AIR3/Ph3CB(C6F5)4
Polymer, 1998Co-Authors: Naofumi Naga, Kooji MizunumaAbstract:Abstract Stereospecific polymerization of propylene was carried out with rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2) (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (rac-Me2Si(Ind)2ZrCl2) (2) and isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (i-Pr(Cp)(Flu)ZrCl2) (3) combined with trialkyl-aluminum (AIR3: R = C2H5, i-C4H9)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (4). In isospecific polymerization with 1 and 2, the molecular weight of Polypropylenes decreased with increase in the molar ratio of AlEt3 (Et = C2H5)/Zr, whereas, an effect of AliBu3 (iBu = i-C4H9) concentration on molecular weight was not observed. The microstructures of resulting Polypropylenes were studied by 13C n.m.r. and an increase in the molar ratio of ethyl end groups (derived from chain transfer to AlEt3) to n-propyl end groups (derived from β-hydrogen transfer) was observed with increase in the molar ratio of AlEt 3 Zr (1 and 2). The chain transfer reactions by both AlEt3 and AliBu3 were also detected in syndiospecific polymerization with 3. The molar ratio of alkyl (R) end groups (derived from chain transfer to AIR3) to n-propyl end groups was higher in the polypropylene obtained with AlEt3 than that obtained with AliBu3. The relative constants k trA k p (ktrA = rate constant of chain transfer to AIR3, kp = rate constant of propagation) were determined by kinetic study.