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ABSTRACT: This work reports the first investigation using the inverse gas chromatography method of a polyimide precursor and the product of its thermal rearrangement (TR polymer), extensively studied earlier. Sorption of gases (CO2, C2H6, C3H8) was studied at the finite dilution regime, while vapors (n-alkanes C7, C8, C10, C14, C16) were investigated at infinite dilution. It was demonstrated that thermal treatment at 450 °C results in a significant increase in the solubility coefficients S for large gas molecules. The absolute values observed for the TR polymer solubility coefficients of solutes are significant and comparable with those for the polymer of intrinsic microporosity (PIM-1), the polymer known by the greatest S values among all of the polymers studied. Sorption thermodynamics in the TR polymer is distinguished by very large and negative mixing parameters: enthalpy h̅1 E,∞ and entropy s1 E,∞.
Industrial & Engineering Chemistry Research 01/2013; · 2.24 Impact Factor
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ABSTRACT: pH-sensitive hydrogels were studied as a drug carrier for the protection of insulin from the acidic environment of the stomach
before releasing it in the small intestine. In this study, hydrogels based on poly(ethylene oxide) (PEO) networks grafted
with methacrylic acid (MAA) or acrylic acid (AAc) were prepared via a two-step process. PEO hydrogels were prepared by γ-ray
irradiation (radiation dose: 50 kGy, dose rate: 7.66 kGy/h), grafted by either MAA or AAc monomers onto the PEO hydrogels
and finally underwent irradiation (radiation dose: 5–20 kGy, dose rate: 2.15 kGy/h). These grafted hydrogels showed a pH-sensitive
swelling behavior. The grafted hydrogels were used as a carrier for the drug delivery systems for the controlled release of
insulin. Drug-loaded hydrogels were placed in simulated gastric fluid (SGF, pH 1.2) for 2 hr and then in simulated intestinal
fluid (SIF, pH 6.8). Thein vitro drug release behaviors of these hydrogels were examined by quantification analysis with a UV-Vis spectrophotometer.
Keywordsradiation–crosslinking–radiation grafting–poly(ethylene oxide)–pH-sensitive hydrogels–drug delivery–insulin
Macromolecular Research 04/2012; 13(4):327-333. · 1.15 Impact Factor
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ABSTRACT: We developed two models for the CO2 separation process by hollow-fiber membrane modules. The explicit model, which is based on mass balances for the separation
modules, is compared with the multilayer perceptrons (MLP) back-propagation neural networks model. Experimental data obtained
from single-stage module with recycle are used to validate the explicit model as well as to train the MLP neural model. The
effectiveness of the model is demonstrated by little discrepancy between experimental data and computational results. The
explicit model for the single-stage module can easily be extended to the multi(three)-stage module. Because of the lack of
experimental data for multi-stage modules, computational data from the explicit model with and without recycle are used as
training data set for the MLP neural model. We examined the effects of recycle on the recovery based on the results of numerical
simulations, and could see that the predicting performance is improved by recycle for multi-stage module. From the results
of numerical simulations, the proposed models can be effectively used in the analysis and operation of gas separation processes
by hollow-fiber membrane modules.
Key wordsMulti-stage Module–Multilayer Perceptrons Back-propagation Networks–Modeling of Separation Process–Carbon Dioxide–Hollow Fiber Membrane
Korean Journal of Chemical Engineering 07/2011; 28(7):1497-1504. · 0.99 Impact Factor
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ABSTRACT: A multi-stage model is developed for CO2 separation by hollow-fiber membrane. The model permits rapid solution of the governing differential mass and pressure distribution
in hollow-fiber gas separation modules using a computational scheme that does not rely on commercial software and conventional
numerical methods such as shooting techniques. For 1-stage, 2-stage and 3-stage configurations the changes of required separation
areas according to stage cuts are computed. A simple model predictive control technique is employed to provide optimal operation
conditions based on the proposed model. Values of stage cuts can easily be identified for various desired mole fractions and
recovery rates. From the results of numerical simulations, we can see that the proposed model can be effectively used in the
control of gas separation process by hollow-fiber membrane modules.
Key wordsMulti-stage Model–Model Predictive Control–Modeling of Separation Process–Carbon Dioxide–Hollow Fiber Membrane
Korean Journal of Chemical Engineering 01/2011; 28(1):41-48. · 0.99 Impact Factor
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ABSTRACT: We developed two models for the CO 2 separation process by hollow-fiber membrane modules. The explicit model, which is based on mass balances for the separation modules, is compared with the multilayer perceptrons (MLP) back-propagation neural networks model. Experimental data obtained from single-stage module with recycle are used to validate the explicit model as well as to train the MLP neural model. The effectiveness of the model is demonstrated by little discrepancy between experimental data and computational results. The explicit model for the single-stage module can easily be extended to the multi(three)-stage module. Because of the lack of experimental data for multi-stage modules, computational data from the explicit model with and without recycle are used as training data set for the MLP neural model. We examined the effects of recycle on the recovery based on the results of numerical simulations, and could see that the predicting performance is improved by recycle for multi-stage module. From the results of numerical simu-lations, the proposed models can be effectively used in the analysis and operation of gas separation processes by hollow-fiber membrane modules.
Korean J. Chem. Eng. 01/2011; 28:1025-1031.
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ABSTRACT: Conversion of hydroxyl-containing polyimides into polybenzoxazole can be achieved by thermal rearrangement of the aromatic polymer chain with decarboxylation at elevated temperature. Synthetic methods to prepare polyimide precursors are important for the resulting thermally rearranged (TR) polymer membranes. Here, we report on the effect of several imidization methods on the properties of TR polymer membranes. Thermal and chemical imidizations are the most common routes to prepare polyimides, and solution thermal imidization using an azeotrope is also widely used, especially to obtain soluble polyimide-containing functional groups. We report here on the syntheses of ortho-functional polyimides from 4,4′-hexafluoroisopropylidene diphthalic anhydrides and 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane by three different imidization methods. Acetate-containing polyimides by chemical imidization and further silylation treatment as well as hydroxyl-containing polyimides by thermal and azeotropic imidization are characterized using thermogravimetric analysis, density, positron annihilation lifetime spectroscopy, and gas permeation property measurements. Comparison between the precursor polyimides and the resulting thermally rearranged polybenzoxazole (TR-PBO) membranes exhibited significant increase in fractional free volumes and cavity sizes followed by enhanced gas permeation properties.
Macromolecules 09/2010; 43(18):7657-7667. · 5.17 Impact Factor
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ABSTRACT: The evolution of micropores in polymer membranes helps accelerate mass transport phenomena on a sub-nanoscale, providing significant technological applications for adsorption, separation and storage. Here we report the synthesis and characterization of thermally rearranged (TR) polymer membranes showing unexpected microporous characters that are often observed in microporous inorganic materials, by using thermal rearrangement of various aromatic polyimides with semi-rigid chain segments in a solid state. Differing from other superglassy polymers (e.g., poly(1-methylsilyl-1-propyne) (PTMSP)) possessing larges cavities, these TR polymer membranes show fast molecular transport as well as a molecular sieving effect for small gas molecules. Micropore structures and their size distributions can be easily tuned by varying the monomer structures of the precursor polymers (i.e., polyimides with ortho-positioned functional groups, PIOFG) and by using different thermal treatment protocols (e.g., final temperature and thermal dwell time). These TR polymer membranes exhibit excellent gas separation performance, especially in carbon dioxide separations (e.g., CO2/CH4), without any paramount plasticization effect. The current approach will be useful in an assessment of the achievements of membrane materials science, providing much insight into new class of microporous polymers.
Journal of Membrane Science 09/2010; 359(1):11-24. · 3.85 Impact Factor
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ABSTRACT: This manuscript reports, for the first time, a new synthesis route to prepare thermally rearranged microporous polybenzimidazole (TR-PBI) membranes, exhibiting exceptionally highly permeable characteristics to small gas molecules as well as excellent molecular sieving properties. Generally, common PBIs have very rigid, well-packed structures due to their strong intermolecular interactions, resulting in very low gas permeation properties which prevent PBIs from applying in gas separation. Here, we demonstrate new synthesis route to obtain highly permeable TR-PBI membranes having microporous characters (i.e., high fractional free volume), prepared by the alkaline hydrolysis of polypyrrolone followed by simple thermal treatment.
Journal of Membrane Science 07/2010; 357(1):143-151. · 3.85 Impact Factor
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ABSTRACT: A series of copolymer membranes was prepared using polyimide (PI) and hydroxyl-containing polyimide (HPI) precursors. Thermal conversion of the hydroxyl-containing imide group into a benzoxazole structure was performed at the solid state to increase rigidity of the polymer backbone, and thus generate free volume elements to improve gas separation performance of the resultant copolymer membrane. Free volume cavities produced during thermal conversion were easily controlled by varying HPI composition in the copolymer. Evidence of thermal conversion was confirmed using spectroscopic and thermogravimetric analysis. O2 permeability of copolymer membranes varied from 0.17 Barrer (1 Barrer = 1 × 10−10 cm3 (STP) cm/cm2 s cmHg) to 220 Barrer depending on membrane composition without a significant loss in selectivity. Also, fully converted polybenzoxazole (PBO) membranes showed high CO2 permeability (1014 Barrer) with a CO2/CH4 selectivity of 24. The copolymer membranes presented here easily overcome the conventional polymeric upper bound limit, and are comparable to the gas separation performance of superior membrane materials such as carbon molecular sieves. The copolymer membrane was also expected to improve the shape properties of the polymer membrane.
Journal of Membrane Science 03/2010; 350(1):301-309. · 3.85 Impact Factor
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ABSTRACT: Poly(benzoxazole-co-pyrrolone) copolymers in various compositions were prepared from thermal rearrangements from their precursors of polyimides containing both hydroxyl and amino groups. All the copolymers showed higher gas permeabilities than their precursors, as well as higher gas selectivity than polybenzoxazole or polypyrrolone homopolymers. Thermally rearranged copolymerization of stiff and selective pyrrolone and high free volume, high permeable benzoxazole moieties are novel routes to enhance gas selectivity without significant losses in gas permeability.
Journal of Membrane Science 03/2010; 349(1):358-368. · 3.85 Impact Factor
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12/2008: pages 633 - 669; , ISBN: 9780470276280
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ABSTRACT: A novel thermoresponsive hydrogel with ion-recognition property was prepared via free-radical cross-linking copolymerization of N-isopropylacrylamide (NIPAM) with benzo-18-crown-6-acrylamide (BCAm) as host receptor. Both chemical structures and stimuli-sensitive properties of the prepared poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) P(NIPAM-co-BCAm) hydrogel were characterized. The smart hydrogel could respond to both temperature and ion stimuli. When the crown ether units captured Ba2+ and formed stable BCAm/Ba2+ host-guest complexes, the lower critical solution temperature (LCST) of the hydrogel increased due to the repulsion among charged BCAm/Ba2+ complex groups and osmotic pressure within the hydrogel. Whereas crown ethers captured Cs+, the LCST shifted to a lower temperature because of the formation of 2:1 sandwich complexes. Unexpectedly, the LCST of the cross-linked P(NIPAM-co-BCAm) hydrogel in K+ solution did not shift to a higher temperature, which was definitely different from the previously reported linear P(NIPAM-co-BCAm) copolymer in K+ solution. The results of this work provide valuable information for development of dual thermo- and ion-responsive hydrogels which have potential applications in drug controlled-release systems or biomedical fields.
The Journal of Physical Chemistry B 02/2008; 112(4):1112-8. · 3.70 Impact Factor
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ABSTRACT: To achieve targeted drug delivery for chemotherapy, a ligand-mediated nanoparticulate drug carrier was designed, which could identify a specific receptor on the surfaces of tumor cells. Biodegradable poly(ethylene oxide)/poly(ε-caprolactone) (PEG/PCL) amphiphilic block copolymers coupled to biotin ligands were synthesized with a variety of PEG/PCL compositions. Block copolymeric nanoparticles harboring the anticancer drug paclitaxel were prepared via micelle formation in aqueous solution. The size of the biotin-conjugated PEG/PCL nanoparticles was determined by light scattering measurements to be 88-118 nm, depending on the molecular weight of the block copolymer, and remained less than 120 nm even after paclitaxel loading. From an in vitro release study, biotin-con-jugated PEG/PCL nanoparticles containing paclitaxel evidenced sustained release profiles of the drug with no initial burst effect. The biotin-conjugated PEG/PCL block copolymer itself evidenced no significant adverse effects on cell viability at 0.005-1.0 μg/mL of nanoparticle suspension regardless of cell type (normal human fibroblasts and HeLa cells). However, biotin-conjugated PEG/PCL harboring paclitaxel evidenced a much higher cytotoxicity for cancer cells than was observed in the PEG/PCL nanoparticles without the biotin group. These results showed that the biotin-conjugated nanoparticles could improve the selective delivery of paclitaxel into cancer cells via interactions with over-expressed biotin receptors on the surfaces of cancer cells.
Macromolecular Research 01/2007; 15:646-655. · 1.15 Impact Factor
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Macromolecular Chemistry and Physics 10/2006; 207(20):1880 - 1887. · 2.36 Impact Factor
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ABSTRACT: The organic solvent with a high partition coefficient toward acid extraction must be selected to increase the efficiency of extraction of acetic acid in aqueous phase. Amine extractant plays a major role in the reactive extraction process at the interface between aqueous phase/organic phases. Therefore, it has been investigated that an effect of addition of various amines such as di-ethylamine (DEA), tri-ethylamine (TEA), and tri-n-octylamine (TOA) to organic phase could increase the extraction performance due to increasing partition coefficient. The effect of temperature with TOA content of 0 to 40 wt-% on extraction process of acetic acid was observed. The removal efficiency of acetic acid in aqueous phase increased with temperature. However, the maximum value of extraction performance was different according to experimental conditions, such as the choice of organic solvent, temperature, and TOA content. In the case of methyl isobutyl ketone (MIBK)/TOA system and chloroform/ TOA used in organic phases, the maximum value of removal of acetic acid showed 64 wt-% and 53 wt-% at 40 wt-% TOA content and 25°C, respectively. In 2-octanol/TOA system, the maximum removal efficiency of acetic acid was 67 wt-% at 30 wt-% TOA and 50°C. On the basis of the energy efficiency, the optimal condition of organic phase for the extraction of acetic acid in aqueous phase was determined to be 40 wt-% MIBK/TOA at 25°C. Using the membrane extraction process with a hollow-fiber membrane contactor, the overall mass transfer coefficient was calculated by Wilson-plot method under the assumption of constant partition coefficient. These values show a significant increase in mass transfer rate with increasing the TOA content. Additionally, an improvement of extraction performance was established by multiplying the diffusion coefficient and partition coefficient of solutes.
Separation Science and Technology 08/2006; 36(3)(457–471 (2001)):457-471. · 1.09 Impact Factor
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ABSTRACT: Novel sulfonated poly(aryl ether ketones) containing benzoxazole were directly synthesized by aromatic nucleophilic polycondensation using various ratios of 2,2'-bi[2-(4-flurophenyl)benzoxazol-6-yl]hexafluoropropane to sodium 5,5'-carbonylbis(2-fluorobenzenesulfonate). The copolymers were soluble in polar aprotic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide at a relatively high solid compo-sition (>15 wt%) and formed tough, flexible and transparent membranes. The membranes exhibited a degradation temperature of above 290 o C. The exact dissolution times of these membranes at 80 o C in Fenton's reagent (3 wt% H 2 O 2 containing 2 ppm FeSO 4) were undetectable, confirming their excellent chemical stability in fuel cell application. The membranes showed a moderate increase in water uptake with respect to increasing temperature. The proton conductivities of the membranes were dependent on the composition and ranged from 1.10× 10 -2 to 5.50×10 -2 Scm -1 at 80 o C and 95% relative humidity (RH). At 120 o C without externally humidified conditions, the conductivities increased above 10 -2 Scm -1 with respect to increasing benzoxazole content, which suggested that the benzoxazole moieties contributed to the proton conduction.
Macromolecular Research 01/2006; 14:438-442. · 1.15 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 10/2005; 43(22):5620 - 5631. · 3.92 Impact Factor
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ABSTRACT: Organic–inorganic hybrid membranes of poly(vinylidene fluoride)-cohexafluoropropylene (PVDF-HFP) and silica composites containing sulfonic acid groups were prepared via in situ polymerization of tetraethoxysilane (TEOS) and sulfosuccinic acid (SSA) using the sol-gel process. The membranes containing more sulfonic acid groups showed a higher vapor sorption and greater swelling behavior. The bound and free water content of the membrane is proportional to the SSA concentration. However, the hybrid membranes without SSA do not have free water. The ion conductivity of the membranes is proportional to the SSA concentration. Silica content in the hybrid membrane without SSA had great effect on their mechanical properties. Tensile modulus and yield stress increased and yield strain and elongation at break decreased with increased silica content. However, in the case of the hybrid membrane containing SSA modulus, yield stress decreased and yield strain and elongation at break increased with increased silica content due to the weak interactions between the hydrophobic polymer chain and the hydrophilic group of SSA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 209–218, 2004
Journal of Applied Polymer Science 07/2004; 93(1):209 - 218. · 1.29 Impact Factor
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ABSTRACT: Sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) membranes and sol-gel derived SPPESK/silica hybrid membranes have been investigated as potential polymer electrolyte membranes for direct methanol fuel cell (DMFC) applications. In comparison with the SPPESK membrane, the SPPESK/silica membranes exhibited higher water content, improved proton conductivity, and lower methanol permeability. Notably, the silica embedded in the membrane acted as a material for reducing the fraction of free water and as a barrier for methanol transport through the membrane. From the results of proton conductivity and methanol permeability studies, we suggest that the fractions of bound and free water should be optimized to obtain desirable proton conductivities and methanol permeabilities. The highly sulfonated PPESK hybrid membrane (HSP-Si) displayed higher proton conductivity (3.42 × 10 2 S/cm) and lower methanol permeability (4.15 × 10 7 cm 2 /s) than those of Nafion 117 (2.54 × 10 2 S/cm; 2.36 × 10 6 cm 2 /s, respectively) at 30 °C. This characteristic of the SPPESK/silica membranes is desirable for future applications related to DMFCs.
Macromolecular Research 01/2004; 12:413-421. · 1.15 Impact Factor
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ABSTRACT: Temperature-sensitive poly(N-isopropylacrylamide) hydrogels were successfully synthesized by using poly(ethylene oxide) as the interpenetrating agent. The newly prepared semi-interpenetrating polymer network (semi-IPN) hydrogels exhibited much better properties as temperature-sensitive polymers than they did in the past. Characterizations of the IPN hydrogels were investigated using a swelling experiment, FTIR spectroscopy, and differential scanning calorimetry (DSC). Semi-IPN hydrogels exhibited a relatively high temperature dependent swelling ratio in the range of 23–28 at room temperature. DSC was used for the determination of the lower critical solution temperature of the semi-IPN hydrogel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3032–3036, 2003
Journal of Applied Polymer Science 10/2003; 90(11):3032 - 3036. · 1.29 Impact Factor
