• Polymer(Korea)
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• v.35 no.1
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• pp.40-46
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• 2011

The synthesis of well-defined poly(styrene-b-isobutylene-b-styrene) (SIBS) triblock copolymers was accomplished by cationic sequential block copolymerization of isobutylene (IB) with styrene (St) using 1,4-di(2-chloro-2-propyl) benzene (DCC) /$TiCl_4$/2,6-di-tert-butylpyridine(DtBP) as an initiating system in methyl chloride ($CH_3Cl$)/methylcyclohexane(MeChx) (50/50 v/v) solvent mixture at $-80^{\circ}C$. The triblock copolymers exhibited excellent thermoplastic and elastomeric characteristics. Tensile strengths and Shore hardness increased with increasing polystyrene (PS) content, while elongation at break decreased. The blood-compatibility of SIBS was assessed by SEM observation of the platelet adhesion, blood clotting time and haemolysis ratio. The haemolysis ratios were below 5% which met the medical materials standard. The platelet adhesion test further indicated that SIBS block copolymers had a good blood compatibility.

• Polymer(Korea)
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• v.36 no.5
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• pp.579-585
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• 2012

Polystyrene/carbon nanotube (CNT) microcellular foams were prepared to have electrically conductive properties via high internal phase emulsion polymerization. In this study, we have investigated the effects of surface modification of CNT, surfactant content and dispersion time to improve the stability of emulsion and the electrical conductivity of foam. Acid treatment and a surfactant were used to effectively disperse CNTs in the aqueous phase. In the organic phase, CNTs were used after a surface modification with organic functional groups. The degree of dispersion of CNTs was estimated by the electrical conductivity of resultant microcellular foams. With raw CNTs dispersed with the surfactant in the aqueous phase, substantial conductivity increase was observed but the foams were slightly shrunk. The foams prepared with organically modified CNTs dispersed in the organic phase showed stable cell morphology without shrinkage, but displayed limitation to improve the conductivity.

• Polymer(Korea)
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• v.37 no.2
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• pp.184-195
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• 2013

Acrylic pressure sensitive adhesive (PSA) tapes were used for the automotive, the electrical and the electronic industries and the display module junction. In this study, the manufacture of high-strength structural tape used 2-ethylhexyl acrylate (2-EHA) and acrylic acid (AAC), and UV irradiation for photo-polymerization, and the semi-structural properties of acrylic PSA tape with the AAC content and inorganic filler $SiO_2$ content were investigated. The initial adhesion strength was lowered by the rigidity of molecule chains due to the use of AAC, and the adhesion strength increased with increasing wetting time. The wetability, contact angle, and SEM images of PSA tapes with various contents of AAC were determined. Without filler, the peel strength and dynamic shear strength of PSA tape showed inverse correlation but the peel strength and dynamic shear strength increased with increasing filler content. From these correlations the PSA tapes could be optimized for the applications requiring high performance.

• Restorative Dentistry and Endodontics
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• v.26 no.5
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• pp.399-408
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• 2001

Tooth bleaching has been prevailing recently for its ability to recover the color and shape of natural teeth without reduction of tooth material. However, it has been reported that bleaching procedure adversely affects the adhesive bond strength of composite resin to tooth. At the same time the bond strength was reported to be regained by application of some chemical agents. The purpose of this in vitro study was to investigate the effect of the removal of residual peroxide on the composite- enamel adhesion and also evaluated fracture mode between resin and enamel after bleaching. Sixty extracted human anterior and premolars teeth were divided into 5 groups and bleached by combined technique using of office bleaching with 35 % hydrogen peroxide and matrix bleaching with 10% carbamide peroxide for 4 weeks. After bleaching, the labial surfaces of each tooth were treated with catalase, 70% ethyl alcohol, distilled water and filled with composite resin. Shear bond strength was tested and the fractured surfaces were also examined with SEM. Analysis revealed significantly higher bond strength values. (p＜0.05) for catalase-treated specimens, but water-treated specimens showed reduction of bond strength, alcohol- treated specimens had medium value between the two groups(p＜0.05). The fracture mode was shown that the catalase group and the alcohol group had cohesive failure but the water sprayed group had adhesive failure. It was concluded that the peroxide residues in tooth after bleaching seems to be removed by gradual diffusion and the free radical oxygen from peroxide prevents polymerization by combining catalyst in the resin monomer. Therefore it may be possible to eliminate the adverse effect on the adhesion of composite resin to enamel after bleaching by using water displacement solution or dentin bonding agent including it for effective removal of residual peroxide.

• Bulletin of the Korean Chemical Society
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• v.29 no.5
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• pp.928-932
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• 2008

A glassy carbon electrode (GCE) modified with poly(p-aminobenzene sulfonic acid) [Poly(p-ABSA)] film is fabricated by voltammetric technique in phosphate buffer solution (pH 8.0) containing $5.0\;{\times}\;10^{-3}\;mol\;L^{-1}$p- ABSA. Electrochemical behaviors of tryptophan at the Poly(p-ABSA) film electrode are investigated with voltammetry. The results indicate that the electrochemical response of tryptophan is improved significantly in the presence of poly(p-ABSA) film. Compared with the bare glassy carbon electrode, the Poly(p-ABSA) film electrode remarkably enhances the irreversible oxidation peak current of tryptophan. Some parameters such as voltammetric sweeping segments for the electrochemical polymerization, pH, accumulation potential and accumulation time are optimized. Under the optimal conditions, the oxidation peak current is proportional to tryptophan concentration in the range of $1.0\;{\times}\;10^{-7}$ to $1.0\;{\times}\;10^{-6}\;mol\;L^{-1}$, and $2.0\;{\times}\;10^{-6}$ to $1.0\;{\times}\;10^{-5}\;mol\;L^{-1}$ with a detection limit of $7.0\;{\times}\;10^{-8}\;mol\;L^{-1}$. The proposed procedure is successfully applied to the determination of tryptophan in a commercial amino acid oral solution.

• Macromolecular Research
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• v.13 no.1
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• pp.45-53
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• 2005

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacryl­amide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator and N,N'-methylenebis­acrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g­PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-poly­methacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the Alg-g-PMAM or the H-Alg-g-PMAM was characterized by FTIR spectroscopy. The effects of the grafting variables (i.e., concentration of MBA, MAM, and APS) and the alkaline hydrolysis conditions (i.e., NaOH concentration, hydrolysis time, and temperature) were optimized systematically to achieve a hydrogel having the maximum swelling capacity. Measurements of the absorbency in various aqueous salt solutions indicated that the swelling capacity decreased upon increasing the ionic strength of the swelling medium. This behavior could be attributed to a charge screening effect for monovalent cations, as well as ionic cross-linking for multivalent cations. Because of the high swelling capacity in salt solutions, however, the hydrogels might be considered as anti-salt superabsorbents. The swelling behavior of the superabsorbing hydrogels was also measured in solutions having values of pH ranging from 1 to 13. Furthermore, the pH reversibility and on/off switching behavior, measured at pH 2.0 and 8.0, suggested that the synthesized hydrogels were excellent candidates for the controlled delivery of bioactive agents. Finally, we performed preliminary investigations of the swelling kinetics of the synthesized hydrogels at various particle sizes.

• Polymer(Korea)
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• v.27 no.6
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• pp.542-548
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• 2003

Nanoparticles with unsaturated poly(hydroxyalkanoate)s (UPHAs) biosynthesized with Pseudo-monas oleovorans were prepared by spontaneous emulsification solvent diffusion method. The influence of nanoparticle formation was investigated with various experimental parameters such as sonication conditions, sol-vent, surfactant and polymer contents, etc. The physical and chemical properties of UPHAS and its nanoparticles were characterized using $^1$H- and $\^$13/C-nuclear magnetic resonance spectroscopies, attenuated total reflection infrared spectroscopy, differential scanning calorimetry and gel permeation chromatography. The morphology of particles was observed using scanning electron microscope and the size and distribution of nanoparticles were measured with electrophoretic light scattering spectrophotometer. The mean diameter of particles decreased with increasing sonication amplitude and time. The addition of ethanol into UPHAS chloroform solution decreased the particle size presumably due to increased solvent diffusion into water phase. The particle size increased with increased the concentration of UPHAS solution. Under the 2-4％ poly(vinyl alcohol) (PVA) aqueous solution the minimum mean diameter of particles was shown. The higher degree of hydrolysis and degree of polymerization of PVA increased the mean diameter of particles.

• Journal of the Korean Applied Science and Technology
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• v.12 no.1
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• pp.101-107
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• 1995

As the surfactants that were used in micellar reaction, emulsion polymerization and phase-transfer reaction etc. have the problems, the cleavable surfactant was converted to inactive compound after such as the reaction in the condition. Because 1, 3-dioxolane ring by ketal or acetal reactioc is lack of stability in acid condition, it is easily made to acid-hydrolysis. And cmc value of the surfactant is assumed $1.0{\times}10^{-5}mol/L$ and surface tension in cmc is 31 dyne/cm. Compared with other surfactant, this surfactant foam property is not better. But emulsion property was relatively good. According as acid-hydrolysis property was observed the interface tension change between aqueous solution and benzene by the variation of pH and time, this surfactant was made to hydrolysis within about 300minutes in pH 1${\sims}$4. Therefore this surfactant is expected to be a good emulsifier that has the bad foam property and the acid-hydrolysis property in acid condition.

• Korean Journal of Food Science and Technology
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• v.22 no.1
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• pp.33-37
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• 1990

A simple and rapid method, based on separation of a flying oil into monomeric, dimeric and oligomeric triglyceride by means of high performance size exclusion chromatography on Ultrastyragel column (500 A), is proposed for evaluation of the quality of used frying oil. The relative area of the monomeric triglyceride was decreased with frying time increase, however, the decrease rate was significantly reduced by treatment of a composited powder (porous rhyorite/citric acid 40/56/4). This measurement showed good linear relationship with change in polar component measurement. There were no significant differences between the slopes of regression lines in both treated and non-treated frying oil system for relationship between monomeric triglyceride and polar component. By this method, it was found that a frying oil habe to be discarded if the content monomeric triglyceride decreased to 71%, which was corresponed to 27% polar component.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.875-879
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• 2008

A method for the depolymerization of polycarbonate waste by glycolysis using ethylene glycol without catalyst was explored in order to get the monomer bisphenol A (BPA). The effect of operation variables such as reaction time, reaction temperature, EG/PC weight ratio and the kinetic of glycolysis were studied. It was found that the polymerization reaction has two different activation energies depending on the reaction temperature. A drop in activation energy with temperature indicates that the reaction mechanism has shifted from one of a succession of elementary steps to another in the series. The maximum yield of BPA of 95.6% was achieved at reaction temperature $220^{\circ}C$ for 85min with EG/PC weight ratio 4.