Gwangsu Byun - Academia.edu (original) (raw)

Papers by Gwangsu Byun

Research paper thumbnail of Structural analysis of thin films of novel polynorbornene derivatives by grazing incidence X-ray scattering and specular X-ray reflectivity along with ellipsometry

Journal of Applied Crystallography, 2006

In the present study, structural analyses using synchrotron grazing incidence Xray scattering, sp... more In the present study, structural analyses using synchrotron grazing incidence Xray scattering, specular reflectivity and ellipsometry were performed on thin films of two novel polynorbornene derivatives, chiral poly(norbornene acid methyl ester) and racemic poly(norbornene acid n-butyl ester), which are potential low dielectric constant materials for advanced microelectronic and display applications. These analyses provided important information on the structure, electron density gradient across the film thickness, chain orientation, refractive index and thermal expansion characteristics of the polymers in substrate-supported thin films. The structural characteristics and properties of the thin films depended on the tacticity of the polymer chain and were further influenced by the film thickness and thermal annealing history.

Research paper thumbnail of Polyamide interfacial composite membranes prepared from m-phenylene diamine, trimesoyl chloride and a new disulfonated diamine

Journal of Membrane Science, 2012

The influence of synthesis conditions (e.g., monomer concentration and membrane preparation proto... more The influence of synthesis conditions (e.g., monomer concentration and membrane preparation protocol) on transport properties of polyamide thin-film composite (TFC) membranes prepared using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization is reported. For example, at 25 • C, NaCl rejection and permeate flux combinations of 99.6 ± 0.1% and 42 ± 3 L/(m 2 h), respectively, were achieved in crossflow filtration using a 2000 ppm aqueous solution of NaCl and a transmembrane pressure difference of 225 psi (15.5 bar). Additionally, a sulfone diamine, disulfonated bis[4-(3-aminophenoxy)phenyl]sulfone (S-BAPS), was used in place of MPD to prepare TFC membranes. The resulting membranes had low NaCl rejection but somewhat higher permeate flux than MPD/TMC membranes. These membranes had reduced chlorine tolerance compared to those prepared using MPD as the diamine.

Research paper thumbnail of Advances in membrane materials: desalination membranes based on directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers

Water Science and Technology, 2010

The water and salt transport properties of chlorine tolerant disulfonated poly(arylene ether sulf... more The water and salt transport properties of chlorine tolerant disulfonated poly(arylene ether sulfone) (BPS) copolymers have been characterized. Cast BPS membranes of both salt form and acid form with sulfonation levels from 20% to 40% were investigated. Water permeability of BPS films increases more than one order of magnitude as sulfonation level increases from 20% to 40%, while the salt permeability of the corresponding membranes increases two orders of magnitude. Moderate salt rejection (98.2%) was achieved by a BPS salt form membrane with a sulfonation level of 20%.

Research paper thumbnail of Pd(II)-catalyzed polymerization of optically active norbornene carboxylic acid esters

Journal of Polymer Science Part A: Polymer Chemistry, 2005

(−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) w... more (−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)-(−)-pantolactone-O-yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)-based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]D = −24.7, polymer [α]D = −98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in 13C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006

Research paper thumbnail of Pd(II)-catalyzed polymerization of optically active norbornene carboxylic acid esters

Journal of Polymer Science Part A: Polymer Chemistry, 2005

(−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) w... more (−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)-(−)-pantolactone-O-yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)-based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]D = −24.7, polymer [α]D = −98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in 13C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006

Research paper thumbnail of Structural analysis of thin films of novel polynorbornene derivatives by grazing incidence X-ray scattering and specular X-ray reflectivity along with ellipsometry

Journal of Applied Crystallography, 2006

In the present study, structural analyses using synchrotron grazing incidence Xray scattering, sp... more In the present study, structural analyses using synchrotron grazing incidence Xray scattering, specular reflectivity and ellipsometry were performed on thin films of two novel polynorbornene derivatives, chiral poly(norbornene acid methyl ester) and racemic poly(norbornene acid n-butyl ester), which are potential low dielectric constant materials for advanced microelectronic and display applications. These analyses provided important information on the structure, electron density gradient across the film thickness, chain orientation, refractive index and thermal expansion characteristics of the polymers in substrate-supported thin films. The structural characteristics and properties of the thin films depended on the tacticity of the polymer chain and were further influenced by the film thickness and thermal annealing history.

Research paper thumbnail of Polyamide interfacial composite membranes prepared from m-phenylene diamine, trimesoyl chloride and a new disulfonated diamine

Journal of Membrane Science, 2012

The influence of synthesis conditions (e.g., monomer concentration and membrane preparation proto... more The influence of synthesis conditions (e.g., monomer concentration and membrane preparation protocol) on transport properties of polyamide thin-film composite (TFC) membranes prepared using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization is reported. For example, at 25 • C, NaCl rejection and permeate flux combinations of 99.6 ± 0.1% and 42 ± 3 L/(m 2 h), respectively, were achieved in crossflow filtration using a 2000 ppm aqueous solution of NaCl and a transmembrane pressure difference of 225 psi (15.5 bar). Additionally, a sulfone diamine, disulfonated bis[4-(3-aminophenoxy)phenyl]sulfone (S-BAPS), was used in place of MPD to prepare TFC membranes. The resulting membranes had low NaCl rejection but somewhat higher permeate flux than MPD/TMC membranes. These membranes had reduced chlorine tolerance compared to those prepared using MPD as the diamine.

Research paper thumbnail of Advances in membrane materials: desalination membranes based on directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers

Water Science and Technology, 2010

The water and salt transport properties of chlorine tolerant disulfonated poly(arylene ether sulf... more The water and salt transport properties of chlorine tolerant disulfonated poly(arylene ether sulfone) (BPS) copolymers have been characterized. Cast BPS membranes of both salt form and acid form with sulfonation levels from 20% to 40% were investigated. Water permeability of BPS films increases more than one order of magnitude as sulfonation level increases from 20% to 40%, while the salt permeability of the corresponding membranes increases two orders of magnitude. Moderate salt rejection (98.2%) was achieved by a BPS salt form membrane with a sulfonation level of 20%.

Research paper thumbnail of Pd(II)-catalyzed polymerization of optically active norbornene carboxylic acid esters

Journal of Polymer Science Part A: Polymer Chemistry, 2005

(−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) w... more (−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)-(−)-pantolactone-O-yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)-based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]D = −24.7, polymer [α]D = −98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in 13C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006

Research paper thumbnail of Pd(II)-catalyzed polymerization of optically active norbornene carboxylic acid esters

Journal of Polymer Science Part A: Polymer Chemistry, 2005

(−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) w... more (−)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)-(−)-pantolactone-O-yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)-based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]D = −24.7, polymer [α]D = −98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in 13C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006