IL KIM - Academia.edu (original) (raw)
Papers by IL KIM
Polymer Bulletin, 1998
SUMMARY SUMMARY Copolymerization of propene and 1-hexene has been carried out in toluene at 30°... more SUMMARY SUMMARY Copolymerization of propene and 1-hexene has been carried out in toluene at 30°C in the presence of homogeneous methylaluminoxane (MAO)-activated 3 ansa-metallocenes, highly syndiospecific iPr(Cp)(Flu)ZrMe2 ( 1 ), lower syndiospecific Et(Cp)(Flu)ZrMe2 ( 2 ), and isospecific rac-(EBTHI)ZrMe2 ( 3 ), in order to study the role of catalyst stereospecificity on comonomer incorporation. The incorporation of 1-hexene decreases in the following order: highly syndiospecific 1 /MAO catalyst > lower syndiospecific 2 /MAO catalyst > isospecific 3 /MAO catalyst. All copolymer chains contain the comonomer in nearly random distribution. The copolymers produced by 1 /MAO and 3 /MAO catalysts were composed of uniform chains, but that by 2 /MAO was fractionated into many fractions in the solvent extraction. Considerable rate enhancements were recorded in the copolymerization when the feed ratio of 1-hexene to propene is around 0.6 for all catalysts.
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL, 2005
In this work, vinyl-functionalized SBA-15 (“vinyl-SBA-15”) was prepared using triethoxyvinylsilan... more In this work, vinyl-functionalized SBA-15 (“vinyl-SBA-15”) was prepared using triethoxyvinylsilane (TEVS) and tetraethoxysilane (TEOS) as co-precursors and a non-ionic triblock copolymer surfactant, EO20PO70EO20, as a template. A direct synthesis grafting (DSG) method was proposed to prepare the vinyl-SBA-15 in order to sustain high loading of organic moieties onto channel wall via one-pot synthesis with maintaining the structural order of the SBA-15 for preparing the vinyl-SBA-15. For comparison, the vinyl-SBA-15 was also prepared by the direct synthesis (DS) method. The method to reduce the synthesis time by quenching was also discussed.
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL, 2004
ABSTRACT
![Research paper thumbnail of Copolymerization of propylene and 1,5-hexadiene with stereospecific metallocene/Al(i-Bu)3/[Ph3C][B(C6F5)4]](https://attachments.academia-assets.com/40565509/thumbnails/1.jpg)
](Journal of Polymer Science Part A: Polymer Chemistry, 2000
Copolymerizations of propylene (P) with 1,5-hexadiene (1,5-HD) were carried out with isospecific ... more Copolymerizations of propylene (P) with 1,5-hexadiene (1,5-HD) were carried out with isospecific rac-1,2-ethylenebis(1-indenyl)Zr(NMe 2 ) 2 [rac-(EBI)Zr(NMe 2 ) 2 , 1] and syndiospecific isopropylidene(cyclopentadienyl)(9-fluorenyl)ZrMe 2 [i-Pr(Cp)-(Flu)ZrMe 2 , 2] compounds combined with Al(i-Bu) 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] as a cocatalyst system. Microstructures of poly(propylene-co-1,5-HD) were determined by 1 H NMR, 13 C NMR, Raman spectroscopies and X-ray powder diffraction. The isospecific 1/Al(i-Bu) 3 /[Ph 3 C][B(C 6 F 6 ) 4 ] catalyst showed much higher polymerization rate than 2/Al(i-Bu) 3 /[Ph 3 C][B(C 6 F 6 ) 4 ] system, however, the latter system showed higher incorporation of 1,5-HD (r P ϭ 8.85, r 1,5-HD ϭ 0.274) than the former system (r P ϭ 16.25, r 1,5-HD ϭ 0.34). The high value of r P ϫ r 1,5-HD far above 1 demonstrated that the copolymers obtained by both catalysts are somewhat blocky. The insertion of 1,5-HD proceeded by enantiomorphic site control; however, the diastereoselectivity of the intramolecular cyclization reaction of 1,2-inserted 1,5-HD was independent of the stereospecificity of metallocene compounds, but dependent on the concentration of 1,5-HD in the feed. The insertion of the monomers by enantiomorphic site control could also be realized by Raman spectroscopy and X-ray powder diffraction of the polymers.
Journal of Polymer Science Part A: Polymer Chemistry, 1999
Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: high... more Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-5 -cyclopentadienyl)(1-5 -fluorenyl)-dimethylzirconium (Me 2 C(Flu)(Cp)ZrMe 2 , 1) and less syndiospecific (1fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe 2 , 2), in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ] as a cocatalyst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smaller dihedral angle showed much higher activity than the 1 compound in the ethylene homo-and copolymerizations. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-hexene comonomer is present in the feed. The copolymerization of ethylene with 1-hexene revealed a noticeable influence of the type of bridge on the relative reactivity of the 1-hexene. 13 C-NMR analysis of copolymers showed that compound 1 is characterized by lower r E , taken as an index of ethylene reactivity, and higher reactivity of 1-hexene. The bridge also affects the distribution of the 1-hexene along the copolymer chain, investigated through their product of reactivity ratios, r E r H . The thermal properties and the density of copolymers were not affected by the type of bridge of the metallocenes, but mainly depended on 1-hexene content in the copolymer.
Journal of Molecular Catalysis A: Chemical, 2010
The tridentate 2,6-bis(benzimidazolyl)pyridine ligands were combined with CoCl 2 to prepare a ser... more The tridentate 2,6-bis(benzimidazolyl)pyridine ligands were combined with CoCl 2 to prepare a series of complexes of the general formula: [Py(Bm-R) 2 ]CoCl 2 (where Py = pyridyl, Bm = benzimidazolyl, R = H (3a); Me (3b); Bz (3c)). These complexes were characterized by ...
Journal of Materials Chemistry, 2010
Adopting a leaching-and fragmentation-free protocol, Ni(II) a-diimine complexes were covalently a... more Adopting a leaching-and fragmentation-free protocol, Ni(II) a-diimine complexes were covalently anchored on nonporous silica without any conventional tedious process. The supported catalysts polymerized ethylene with activities > 10 6 g-PE mol-Ni À1 h À1 bar À1 (10 kg-PE g-cat À1 at 5.5 bar pressure) when activated with a small amount (Al/Ni $100) of common aluminium alkyls (ethylaluminium sesquichloride, methylaluminium dichloride, and diethylaluminium chloride) in the absence of any methylaluminoxane. The polymer growth pattern from uniform spheres to fibers was clearly traced by using this model supported system, which depends on the catalytic activity, metal loading, and effective selection of co-catalysts. The polymerization results were compared with conventional porous silica supports immobilized by the same complex that undergoes fragmentation leading to a poor PE morphology. † Electronic supplementary information (ESI) available: Synthesis of ligands, complexes and silica-gel, SEM and TEM images of catalysts and polymers, DSC of polymers. See
ChemPhysChem, 2008
There has been considerable interest in recent years in using metal, semiconductor, and magnetic ... more There has been considerable interest in recent years in using metal, semiconductor, and magnetic nanoparticles in biological applications. A wide range of ligation and encapsulation methods have been developed to render the nanoparticles soluble in aqueous solution, to prevent aggregation, and to provide means by which functional molecules can be attached. Among these methods, encapsulation of nanoparticles by a polymer, phospholipid, or inorganic shell is of particular interest to us, since these stable shells prevent dissociation of surface ligands and provide anchor points where biomolecules are unlikely to be lost once attached. This is a significant advantage over direct conjugation through surface ligands, since even strong thiol ligands can dissociate from or undergo exchange on gold surfaces, let alone weaker ligands on the surfaces of quantum dots or magnetic nanoparticles. Stable attachment of biomolecules would be particularly important where only a few biomolecules are selectively attached to a nanoparticle, or when multiple types of singly functionalized nanoparticles are mixed.
Catalysis Today, 2011
A new trimetallic heterotrinuclear catalyst bearing two Fe and one Ni atoms of the general formul... more A new trimetallic heterotrinuclear catalyst bearing two Fe and one Ni atoms of the general formula {(2,6-C12H17)NC–(C7H9N)[FeCl2]C–NC–(C23H34)–C}2N–C–(C10H6)–CN[NiBr2] has been synthesized successfully. For comparison, monometallic Ni(II) and bimetallic Fe(II) complexes are also investigated. When activated with methylaluminoxane or common alkyl aluminums such as ethyl aluminum sesquichloride and triethylaluminum, all catalysts polymerize ethylene with activities exceeding 105g-PE/mol-Mhbar at 30°C. The heteronuclear trimetallic complexes showed higher catalytic activity and longer life time, especially at high temperature, than monometallic Ni(II) and homonuclear bimetallic Fe analogues, due to the cooperative effect of the neighboring metals. The molecular weight, polydispersity and the degree of branching of polyethylene were drastically influenced by the type of the metal complex and experimental parameters.
Catalysis Surveys from Asia, 2006
In this review article, we have consolidated our recent studies on late transition metal catalyst... more In this review article, we have consolidated our recent studies on late transition metal catalysts (mainly Fe, Co) for olefin polymerization/oligomerization. A series of bisiminopyridyl Co(II) and Fe(II) complexes were synthesized. These catalysts when activated with MAO in aromatic or aliphatic hydrocarbon solvents, oligomerize or polymerize ethylene to a-olefins or high molecular weight polymers with exceptionally high activities and selectivities. The electronic and steric effects of allyloxy and benzyloxy substituted bisiminopyridyl Fe(II) and Co(II) complexes were also investigated. The influence of catalyst structure and temperature on the polymerization activity, thermal properties and molecular weight were discussed. The effects of heterogenization of these catalysts on silica and modified SBA-15 were analyzed. The polymerization of polar monomers such as vinyl ethers and methyl methacrylate was tested and no specific trends in activity and polymer molecular weight with changes in steric bulkiness around the metal center were observed with the same catalyst system.
IEEE Photonics Technology Letters, 2000
Spectral equalization devices for an optical analog-todigital (A-to-D) converting system have bee... more Spectral equalization devices for an optical analog-todigital (A-to-D) converting system have been theoretically analyzed and fabricated. Selective area growth was used to define a multiplesection active region. Two-segment semiconductor optical amplifier with current adjustable gain spectrum is demonstrated.
Rheumatology International, 2012
PXK was identified as a novel candidate gene for systemic lupus erythematosus (SLE) from genome-w... more PXK was identified as a novel candidate gene for systemic lupus erythematosus (SLE) from genome-wide association studies (GWAS) in Caucasians. But a recent replication study in Hong Kong Chinese reported that PXK was not associated with SLE. The aim of this study was to determine whether PXK is associated with SLE in Koreans. We genotyped single nucleotide polymorphism (SNP) rs6445975 of PXK using the TaqMan assay in 527 Korean patients with SLE and 517 healthy Korean control subjects. Genotypic associations were assessed using multiple logistic regression models. Additional analyses were also performed by subphenotype stratification. No association was detected between PXK rs6445975 and SLE (odds ratio (OR) = 1.06, P = 0.57). PXK rs6445975 showed positive associations with photosensitivity (P = 0.02) and the production of anti-Sm Ab (P = 0.04) among SLE patients. Thus, the association of PXK rs6445975 with SLE that was previously observed in Caucasians was not replicated in Koreans or in Hong Kong Chinese. It is possible that PXK has different genetic contribution on SLE between Caucasians and Asians and that the gene is associated with disease subphenotypes rather than with overall susceptibility.
Polymer Bulletin, 2004
Copolymerizations of ethylene with 1-decene were carried out with a series of stereospecific meta... more Copolymerizations of ethylene with 1-decene were carried out with a series of stereospecific metallocene compounds, C2H4[Ind]2Zr(NMe2)2 (1), C2H4[Ind]2Hf(NMe2)2 (2), (CH3)2Si(1-C5H2-2-CH3-4-tC4H9)2Zr(NMe2)2 (3), C2H4(Fluo)(Cp)Zr(NMe2)2 (4), (CH3)2C(Fluo)(Cp)Zr(NMe2)2 (5) (Cp = η5-cyclopen-tadienyl, Ind = η5-indenyl Fluo = η5-fluorenyl), combined with Al(i-Bu)3/[CPh3][B(C6F5)4] cocatalyst. The copolymerization rate decreased in the order of 3 > 1 > 2 ∼ 4 > 5 and the 1-decene reactivity decreased in the order of 2 > 5 > 1 ∼ 4 > 3. The reactivity product of ethylene and 1-decene (rE × rD) was below 1 except 3 catalyst, corresponding to random copolymer structures with an alternating character. The melting point, crystallinity, intrinsic viscosity and density of the 1-decene/ethylene copolymers decreased markedly with an increase in the 1-decene content, regardless of the type of catalytic system.
Molecular Crystals and Liquid Crystals, 2007
ABSTRACT
Macromolecular Research, 2006
Abstract In the present work, low density polyethylene (LDPE)/aliphatic polyester (APES)/organocl... more Abstract In the present work, low density polyethylene (LDPE)/aliphatic polyester (APES)/organoclay ternary nanocomposites were prepared. In particular, the effect of a compatibilizer, polyethylene-graft-maleic anhydride (PE-g-MAH), on the morphology and ...
Macromolecular Rapid Communications, 2009
Langmuir, 2008
By means of a plasma technique, the surfaces of monodisperse polystyrene (PS) colloids have been ... more By means of a plasma technique, the surfaces of monodisperse polystyrene (PS) colloids have been modified with hydroxyl groups. Using these surface-modified PS colloids as sacrificial templates, we have fabricated silica-coated PS colloids (PS@silica) and titania-coated PS colloids (PS@titania) composite microspheres as well as hollow and mesoporous silica and titania microspheres. This process not only demonstrated a facile, low-cost, environmentally benign way to fabricate hollow oxides structures but also offered a feasible alternative to the preparation of polymer/ inorganic oxide composites by templating against the polymer substrate with hydrophobic surfaces. Figure 3. (a) SEM and (b) TEM images of hollow silica microspheres. (c) SEM and (d) TEM images of hollow titania microspheres. The scale bars are 400 nm, and the scale bars in insets are 200 nm.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008
ABSTRACT The structural characterizations of aromatic polyimide (PI) ultra-thin films with differ... more ABSTRACT The structural characterizations of aromatic polyimide (PI) ultra-thin films with different fluorine contents were studied. Three types of polyamic acid (PAA) were produced from polymerization of biphenyl dianhydride (BPDA)/4,4′-oxydianiline (ODA), BPDA/2,2′-bis(trifluromethyl)benzidine (TFDB), and 4,4′-(hexafluoro isopropylidene)-diphthalic anhydride (6FDA)/TFDB in N,N-dimethylacetamide (DMAc). Polyamic acid alkyl salts (PAAS) using O,O′,O″-trihexadecanoyl-triethanolamine were transferred onto a Si-wafer substrate to prepare Langmuir–Blodgett (LB) films. The behaviors of PAAS monolayers at the air/water interface were confirmed with π–A isotherms and Brewster Angle Microscopy (BAM) images. The behaviors of PAAS monolayers at the air/water interface depend on the fluorine contents. As there is more fluorine in the main chain of PAAS, the area per molecule of each monolayer was increased. The structure of PAAS LB films with 10, 20, 30, and 40 layers on a substrate were investigated by UV–vis spectroscopy, X-ray diffraction (XRD), X-ray reflectivity, and IR spectroscopy. The obtained PAAS LB films were imidized with a thermal treatment at 300°C. The imidization of PI ultra-thin film was identified by IR spectrum. Atomic force microscopy (AFM) images showed that the particle size of PI ultra-thin films on a Si-wafer were about 7–25nm.
Chemistry of Materials, 2003
Much progress has been made recently in the preparation of a new class of organic−inorganic hybri... more Much progress has been made recently in the preparation of a new class of organic−inorganic hybrid materials called periodic mesoporous organosilicas (PMOs) through surfactant-templated condensation of organosilanes with two trialkoxysilyl groups bridged by an organic group. ...
Catalysis Today, 2004
The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studi... more The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studied over niobium-iron mixed oxide catalysts. They showed very high conversion of H2S with lower than 2% of SO2 selectivity. The addition of niobium oxide to iron oxide increased H2S conversion until Nb/Fe atomic ratio of 1/2, then the conversion decreased as the Nb/Fe ratio
Polymer Bulletin, 1998
SUMMARY SUMMARY Copolymerization of propene and 1-hexene has been carried out in toluene at 30°... more SUMMARY SUMMARY Copolymerization of propene and 1-hexene has been carried out in toluene at 30°C in the presence of homogeneous methylaluminoxane (MAO)-activated 3 ansa-metallocenes, highly syndiospecific iPr(Cp)(Flu)ZrMe2 ( 1 ), lower syndiospecific Et(Cp)(Flu)ZrMe2 ( 2 ), and isospecific rac-(EBTHI)ZrMe2 ( 3 ), in order to study the role of catalyst stereospecificity on comonomer incorporation. The incorporation of 1-hexene decreases in the following order: highly syndiospecific 1 /MAO catalyst > lower syndiospecific 2 /MAO catalyst > isospecific 3 /MAO catalyst. All copolymer chains contain the comonomer in nearly random distribution. The copolymers produced by 1 /MAO and 3 /MAO catalysts were composed of uniform chains, but that by 2 /MAO was fractionated into many fractions in the solvent extraction. Considerable rate enhancements were recorded in the copolymerization when the feed ratio of 1-hexene to propene is around 0.6 for all catalysts.
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL, 2005
In this work, vinyl-functionalized SBA-15 (“vinyl-SBA-15”) was prepared using triethoxyvinylsilan... more In this work, vinyl-functionalized SBA-15 (“vinyl-SBA-15”) was prepared using triethoxyvinylsilane (TEVS) and tetraethoxysilane (TEOS) as co-precursors and a non-ionic triblock copolymer surfactant, EO20PO70EO20, as a template. A direct synthesis grafting (DSG) method was proposed to prepare the vinyl-SBA-15 in order to sustain high loading of organic moieties onto channel wall via one-pot synthesis with maintaining the structural order of the SBA-15 for preparing the vinyl-SBA-15. For comparison, the vinyl-SBA-15 was also prepared by the direct synthesis (DS) method. The method to reduce the synthesis time by quenching was also discussed.
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL, 2004
ABSTRACT
Journal of Polymer Science Part A: Polymer Chemistry, 2000
Copolymerizations of propylene (P) with 1,5-hexadiene (1,5-HD) were carried out with isospecific ... more Copolymerizations of propylene (P) with 1,5-hexadiene (1,5-HD) were carried out with isospecific rac-1,2-ethylenebis(1-indenyl)Zr(NMe 2 ) 2 [rac-(EBI)Zr(NMe 2 ) 2 , 1] and syndiospecific isopropylidene(cyclopentadienyl)(9-fluorenyl)ZrMe 2 [i-Pr(Cp)-(Flu)ZrMe 2 , 2] compounds combined with Al(i-Bu) 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] as a cocatalyst system. Microstructures of poly(propylene-co-1,5-HD) were determined by 1 H NMR, 13 C NMR, Raman spectroscopies and X-ray powder diffraction. The isospecific 1/Al(i-Bu) 3 /[Ph 3 C][B(C 6 F 6 ) 4 ] catalyst showed much higher polymerization rate than 2/Al(i-Bu) 3 /[Ph 3 C][B(C 6 F 6 ) 4 ] system, however, the latter system showed higher incorporation of 1,5-HD (r P ϭ 8.85, r 1,5-HD ϭ 0.274) than the former system (r P ϭ 16.25, r 1,5-HD ϭ 0.34). The high value of r P ϫ r 1,5-HD far above 1 demonstrated that the copolymers obtained by both catalysts are somewhat blocky. The insertion of 1,5-HD proceeded by enantiomorphic site control; however, the diastereoselectivity of the intramolecular cyclization reaction of 1,2-inserted 1,5-HD was independent of the stereospecificity of metallocene compounds, but dependent on the concentration of 1,5-HD in the feed. The insertion of the monomers by enantiomorphic site control could also be realized by Raman spectroscopy and X-ray powder diffraction of the polymers.
Journal of Polymer Science Part A: Polymer Chemistry, 1999
Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: high... more Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-5 -cyclopentadienyl)(1-5 -fluorenyl)-dimethylzirconium (Me 2 C(Flu)(Cp)ZrMe 2 , 1) and less syndiospecific (1fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe 2 , 2), in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ] as a cocatalyst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smaller dihedral angle showed much higher activity than the 1 compound in the ethylene homo-and copolymerizations. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-hexene comonomer is present in the feed. The copolymerization of ethylene with 1-hexene revealed a noticeable influence of the type of bridge on the relative reactivity of the 1-hexene. 13 C-NMR analysis of copolymers showed that compound 1 is characterized by lower r E , taken as an index of ethylene reactivity, and higher reactivity of 1-hexene. The bridge also affects the distribution of the 1-hexene along the copolymer chain, investigated through their product of reactivity ratios, r E r H . The thermal properties and the density of copolymers were not affected by the type of bridge of the metallocenes, but mainly depended on 1-hexene content in the copolymer.
Journal of Molecular Catalysis A: Chemical, 2010
The tridentate 2,6-bis(benzimidazolyl)pyridine ligands were combined with CoCl 2 to prepare a ser... more The tridentate 2,6-bis(benzimidazolyl)pyridine ligands were combined with CoCl 2 to prepare a series of complexes of the general formula: [Py(Bm-R) 2 ]CoCl 2 (where Py = pyridyl, Bm = benzimidazolyl, R = H (3a); Me (3b); Bz (3c)). These complexes were characterized by ...
Journal of Materials Chemistry, 2010
Adopting a leaching-and fragmentation-free protocol, Ni(II) a-diimine complexes were covalently a... more Adopting a leaching-and fragmentation-free protocol, Ni(II) a-diimine complexes were covalently anchored on nonporous silica without any conventional tedious process. The supported catalysts polymerized ethylene with activities > 10 6 g-PE mol-Ni À1 h À1 bar À1 (10 kg-PE g-cat À1 at 5.5 bar pressure) when activated with a small amount (Al/Ni $100) of common aluminium alkyls (ethylaluminium sesquichloride, methylaluminium dichloride, and diethylaluminium chloride) in the absence of any methylaluminoxane. The polymer growth pattern from uniform spheres to fibers was clearly traced by using this model supported system, which depends on the catalytic activity, metal loading, and effective selection of co-catalysts. The polymerization results were compared with conventional porous silica supports immobilized by the same complex that undergoes fragmentation leading to a poor PE morphology. † Electronic supplementary information (ESI) available: Synthesis of ligands, complexes and silica-gel, SEM and TEM images of catalysts and polymers, DSC of polymers. See
ChemPhysChem, 2008
There has been considerable interest in recent years in using metal, semiconductor, and magnetic ... more There has been considerable interest in recent years in using metal, semiconductor, and magnetic nanoparticles in biological applications. A wide range of ligation and encapsulation methods have been developed to render the nanoparticles soluble in aqueous solution, to prevent aggregation, and to provide means by which functional molecules can be attached. Among these methods, encapsulation of nanoparticles by a polymer, phospholipid, or inorganic shell is of particular interest to us, since these stable shells prevent dissociation of surface ligands and provide anchor points where biomolecules are unlikely to be lost once attached. This is a significant advantage over direct conjugation through surface ligands, since even strong thiol ligands can dissociate from or undergo exchange on gold surfaces, let alone weaker ligands on the surfaces of quantum dots or magnetic nanoparticles. Stable attachment of biomolecules would be particularly important where only a few biomolecules are selectively attached to a nanoparticle, or when multiple types of singly functionalized nanoparticles are mixed.
Catalysis Today, 2011
A new trimetallic heterotrinuclear catalyst bearing two Fe and one Ni atoms of the general formul... more A new trimetallic heterotrinuclear catalyst bearing two Fe and one Ni atoms of the general formula {(2,6-C12H17)NC–(C7H9N)[FeCl2]C–NC–(C23H34)–C}2N–C–(C10H6)–CN[NiBr2] has been synthesized successfully. For comparison, monometallic Ni(II) and bimetallic Fe(II) complexes are also investigated. When activated with methylaluminoxane or common alkyl aluminums such as ethyl aluminum sesquichloride and triethylaluminum, all catalysts polymerize ethylene with activities exceeding 105g-PE/mol-Mhbar at 30°C. The heteronuclear trimetallic complexes showed higher catalytic activity and longer life time, especially at high temperature, than monometallic Ni(II) and homonuclear bimetallic Fe analogues, due to the cooperative effect of the neighboring metals. The molecular weight, polydispersity and the degree of branching of polyethylene were drastically influenced by the type of the metal complex and experimental parameters.
Catalysis Surveys from Asia, 2006
In this review article, we have consolidated our recent studies on late transition metal catalyst... more In this review article, we have consolidated our recent studies on late transition metal catalysts (mainly Fe, Co) for olefin polymerization/oligomerization. A series of bisiminopyridyl Co(II) and Fe(II) complexes were synthesized. These catalysts when activated with MAO in aromatic or aliphatic hydrocarbon solvents, oligomerize or polymerize ethylene to a-olefins or high molecular weight polymers with exceptionally high activities and selectivities. The electronic and steric effects of allyloxy and benzyloxy substituted bisiminopyridyl Fe(II) and Co(II) complexes were also investigated. The influence of catalyst structure and temperature on the polymerization activity, thermal properties and molecular weight were discussed. The effects of heterogenization of these catalysts on silica and modified SBA-15 were analyzed. The polymerization of polar monomers such as vinyl ethers and methyl methacrylate was tested and no specific trends in activity and polymer molecular weight with changes in steric bulkiness around the metal center were observed with the same catalyst system.
IEEE Photonics Technology Letters, 2000
Spectral equalization devices for an optical analog-todigital (A-to-D) converting system have bee... more Spectral equalization devices for an optical analog-todigital (A-to-D) converting system have been theoretically analyzed and fabricated. Selective area growth was used to define a multiplesection active region. Two-segment semiconductor optical amplifier with current adjustable gain spectrum is demonstrated.
Rheumatology International, 2012
PXK was identified as a novel candidate gene for systemic lupus erythematosus (SLE) from genome-w... more PXK was identified as a novel candidate gene for systemic lupus erythematosus (SLE) from genome-wide association studies (GWAS) in Caucasians. But a recent replication study in Hong Kong Chinese reported that PXK was not associated with SLE. The aim of this study was to determine whether PXK is associated with SLE in Koreans. We genotyped single nucleotide polymorphism (SNP) rs6445975 of PXK using the TaqMan assay in 527 Korean patients with SLE and 517 healthy Korean control subjects. Genotypic associations were assessed using multiple logistic regression models. Additional analyses were also performed by subphenotype stratification. No association was detected between PXK rs6445975 and SLE (odds ratio (OR) = 1.06, P = 0.57). PXK rs6445975 showed positive associations with photosensitivity (P = 0.02) and the production of anti-Sm Ab (P = 0.04) among SLE patients. Thus, the association of PXK rs6445975 with SLE that was previously observed in Caucasians was not replicated in Koreans or in Hong Kong Chinese. It is possible that PXK has different genetic contribution on SLE between Caucasians and Asians and that the gene is associated with disease subphenotypes rather than with overall susceptibility.
Polymer Bulletin, 2004
Copolymerizations of ethylene with 1-decene were carried out with a series of stereospecific meta... more Copolymerizations of ethylene with 1-decene were carried out with a series of stereospecific metallocene compounds, C2H4[Ind]2Zr(NMe2)2 (1), C2H4[Ind]2Hf(NMe2)2 (2), (CH3)2Si(1-C5H2-2-CH3-4-tC4H9)2Zr(NMe2)2 (3), C2H4(Fluo)(Cp)Zr(NMe2)2 (4), (CH3)2C(Fluo)(Cp)Zr(NMe2)2 (5) (Cp = η5-cyclopen-tadienyl, Ind = η5-indenyl Fluo = η5-fluorenyl), combined with Al(i-Bu)3/[CPh3][B(C6F5)4] cocatalyst. The copolymerization rate decreased in the order of 3 > 1 > 2 ∼ 4 > 5 and the 1-decene reactivity decreased in the order of 2 > 5 > 1 ∼ 4 > 3. The reactivity product of ethylene and 1-decene (rE × rD) was below 1 except 3 catalyst, corresponding to random copolymer structures with an alternating character. The melting point, crystallinity, intrinsic viscosity and density of the 1-decene/ethylene copolymers decreased markedly with an increase in the 1-decene content, regardless of the type of catalytic system.
Molecular Crystals and Liquid Crystals, 2007
ABSTRACT
Macromolecular Research, 2006
Abstract In the present work, low density polyethylene (LDPE)/aliphatic polyester (APES)/organocl... more Abstract In the present work, low density polyethylene (LDPE)/aliphatic polyester (APES)/organoclay ternary nanocomposites were prepared. In particular, the effect of a compatibilizer, polyethylene-graft-maleic anhydride (PE-g-MAH), on the morphology and ...
Macromolecular Rapid Communications, 2009
Langmuir, 2008
By means of a plasma technique, the surfaces of monodisperse polystyrene (PS) colloids have been ... more By means of a plasma technique, the surfaces of monodisperse polystyrene (PS) colloids have been modified with hydroxyl groups. Using these surface-modified PS colloids as sacrificial templates, we have fabricated silica-coated PS colloids (PS@silica) and titania-coated PS colloids (PS@titania) composite microspheres as well as hollow and mesoporous silica and titania microspheres. This process not only demonstrated a facile, low-cost, environmentally benign way to fabricate hollow oxides structures but also offered a feasible alternative to the preparation of polymer/ inorganic oxide composites by templating against the polymer substrate with hydrophobic surfaces. Figure 3. (a) SEM and (b) TEM images of hollow silica microspheres. (c) SEM and (d) TEM images of hollow titania microspheres. The scale bars are 400 nm, and the scale bars in insets are 200 nm.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008
ABSTRACT The structural characterizations of aromatic polyimide (PI) ultra-thin films with differ... more ABSTRACT The structural characterizations of aromatic polyimide (PI) ultra-thin films with different fluorine contents were studied. Three types of polyamic acid (PAA) were produced from polymerization of biphenyl dianhydride (BPDA)/4,4′-oxydianiline (ODA), BPDA/2,2′-bis(trifluromethyl)benzidine (TFDB), and 4,4′-(hexafluoro isopropylidene)-diphthalic anhydride (6FDA)/TFDB in N,N-dimethylacetamide (DMAc). Polyamic acid alkyl salts (PAAS) using O,O′,O″-trihexadecanoyl-triethanolamine were transferred onto a Si-wafer substrate to prepare Langmuir–Blodgett (LB) films. The behaviors of PAAS monolayers at the air/water interface were confirmed with π–A isotherms and Brewster Angle Microscopy (BAM) images. The behaviors of PAAS monolayers at the air/water interface depend on the fluorine contents. As there is more fluorine in the main chain of PAAS, the area per molecule of each monolayer was increased. The structure of PAAS LB films with 10, 20, 30, and 40 layers on a substrate were investigated by UV–vis spectroscopy, X-ray diffraction (XRD), X-ray reflectivity, and IR spectroscopy. The obtained PAAS LB films were imidized with a thermal treatment at 300°C. The imidization of PI ultra-thin film was identified by IR spectrum. Atomic force microscopy (AFM) images showed that the particle size of PI ultra-thin films on a Si-wafer were about 7–25nm.
Chemistry of Materials, 2003
Much progress has been made recently in the preparation of a new class of organic−inorganic hybri... more Much progress has been made recently in the preparation of a new class of organic−inorganic hybrid materials called periodic mesoporous organosilicas (PMOs) through surfactant-templated condensation of organosilanes with two trialkoxysilyl groups bridged by an organic group. ...
Catalysis Today, 2004
The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studi... more The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studied over niobium-iron mixed oxide catalysts. They showed very high conversion of H2S with lower than 2% of SO2 selectivity. The addition of niobium oxide to iron oxide increased H2S conversion until Nb/Fe atomic ratio of 1/2, then the conversion decreased as the Nb/Fe ratio