• Elastomers and Composites
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• v.53 no.3
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• pp.158-167
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• 2018

In this study, in-situ trans-selective polymerization of isoprene was carried out using titanium-based Ziegler-Natta catalysts. The catalysts were prepared by high-energy ball milling. Individually Large-inner-diameter carbon nanotubes (CNTL), and hydroxylated carbon nanotubes (CNTOH), along with magnesium chloride ($MgCl_2$) were used as the carriers for the catalysts. The optimum ball-milling time for preparing the $CNT/MgCl_2/TiCl_4$ Ziegler-Natta catalysts was 4 h. The $CNTOH/MgCl_2/TiCl_4$ catalyst showed a higher efficiency than that of the $CNTL/MgCl_2/TiCl_4$ catalyst, based on the rate of polymerization. The effects of the CNT-filler type on the isoprene polymerization behaviors and polymer properties were investigated. The morphologies of the trans-1,4-polyisoprene (TPI)/CNT and TPI/CNTOH nanocomposites exhibited a tube-like shape, and the CNTL and CNTOH fillers were well dispersed in the TPI matrix. In addition, the thermal stability of TPI significantly increased upon the introduction of a small amount of both CNTL/CNTOH fillers (0.15 wt%), owing to the satisfactory dispersion of the CNTL/CNTOH in the TPI matrix.

• Korean Journal of Veterinary Research
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• v.35 no.3
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• pp.531-536
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• 1995

Salmonella species are the most prevalent etiologic agents of food-borne acute gastroenteritis. Direct isolation of bacteria from the contaminated food, stool and animal tissues has been used for the diagnosis of salmonellosis routinely. However, isolation of bacteria is time consuming work and not so highly sensitive. In recent years, improved methods of polymerization chain reaction(PCR) and probe hybridization technique have led to the developement of diagnostic assays which employ to detect various human and animal pathogenic bacteria. In this study, we have performed the polymerization chain reaction to detect Salmonella pullorum from tissues and stool samples of chickens with two specific primers, ST5 and ST8C. The target DNA fragment of PhoE gene was successfully amplified from liver, spleen, pancreas, heart, lung, ovary, oviduct and feces samples. The amplified DNA fragments were hybridized with Salmonella typhymurium TA3000 PhoE probe by Southern hybridization. The PCR to amplify the PhoE gene was highly rapid and sensitive method to detect Salmonella pullorum from tissues and stool samples.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.3
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• pp.554-563
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• 1999

For the purpose of elucidating the polymerization modes of dual-cure restorative materials and comparing them with single-cure restorative materials, a study was performed on the light-cured composite resin, dual-cure composite resin, dual-cure glass ionomer cement and chemical-cure glass ionomer cement. By measuring the microhardness of each material at 0mm, 1mm and 3mm depth during initial 24 hours with predetermined interval, the state of polymerization and degree of conversion was indirectly evaluated for each material, and obtained results are as follows : 1. All of four materials tested showed significant increase in microhardness after 24hrs compared with just after curing starts. 2. In all materials except Ketac-fil, there showed a significant difference in microhardness between each depth at each time interval. 3. In the test of lap time till final curing for each material, the polymerization process was revealed to last longer in the dual-cure type materials than in single-cure type materials at 3mm depth. Based on the results above, it was demonstrated with materials of dual-cure mode that the degree of conversion increases by successive curing reactions even in the deeper layers where sufficient curing light is impermeable.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.844-852
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• 1997

In the polymerization of ethylene to produce crystalline polyethylene wax using the homogeneous titanium-based catalyst, the effects of various parameters such as catalyst, temperature, pressure, comonomer and time on the performance of catalyst and the properties of polyethylene wax were investigated. The properties of polyethylene wax obtained were characterized in terms of molecular weight, molecular weight distribution, crystallinity, density and morphology. Among the polymerization features with a series of mixed cocatalyst systems of $(C_2H_5)_3Al$, $(i-C_4H_9)_3Al$, $(C_2H_5)_2AlCl$ and $(C_2H_5)_3Al_2Cl_3$, it turned out that the combination of $(C_2H_5)_3Al$ and $(C_2H_5)_3Al_2Cl_3$ was more effective than any other combination. It was noted that the activity of catalyst and the properties of polyethylene wax were affected by the polymerization parameters, i.e. time, temperature and hydrogen partial pressure. The various kinds of crystalline polyethylene wax could be obtained by careful control of these parameters. Also we could obtain low density polyethylene wax which has density down to 0.91 g/cc by use of 1-butene as a comonomer.

• Elastomers and Composites
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• v.48 no.4
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• pp.263-268
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• 2013

In this study, we prepared poly(ethylene-ter-1-hexene-ter-divinylbenzene) using bridged rac-$Et[Ind]_2ZrCl_2$ metallocene catalysts. The effect of 1-hexene on the terpolymerization rate was evaluated. When cocatalyst/catalyst molar ratio was 3,000, catalytic activity indicated more than 8,000 which was very remarkable value. As polymerization time increased, the weight-average molecular weight of the terpolymer gradually increased to some degree. In case of a polymerization time of 50 minutes, the terpolymer became amorphous state. The molecular weight distribution and densities of the terpolymer were 110,000-200,000 and $0.85-0.89g/cm^3$, respectively. Thermal properties and structure of the terpolymer were also identified.

• Polymer(Korea)
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• v.29 no.4
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• pp.418-421
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• 2005

Three-dimensional (3D) microfabrication process using two-photon polymerization (TPP) is developed to fabricate the curved microstructures in a layer, which can be applied potentially to optical MEMS, nano/micro-devices, etc. A 3D curved structure can be expressed using the same height-contours that are defined by symbolic colors which consist of 14 colors. Then, the designed bitmap figure is transformed into a multi-exposure voxel matrix (MVM). In this work a multi-exposure voxel matrix scanning method is used to generate various heights of voxels according to each laser exposure time that is assigned to the symbolic colors. An objective lens with a numerical aperture of 1.25 is employed to enlarge the variation of a voxel height in the range of 1.2 to 6.4 um which can be controlled easily using the various exposure time. Though this work some 3D curved micro-shapes are fabricated directly to demonstrate the usefulness of the process without a laminating process that is generally required in a micro-stereolithography process.

• Membrane Journal
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• v.8 no.1
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• pp.29-41
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• 1998

Thin-film composite reverse osmosis membranes of aromatic polyamides were prepared by the interfacial polymerization. Aromatic polyamides as active skin layer were made from the interfacial polymerization of MPD(m-phenylene diamine) in the aqueous and TMC(trimesoyl chloride) in HCFC(1,1-dichloro-1-fluoroethane) organic solvent. The performances of the various reverse osmosis composite membranes prepared by changing processing variables were examined. The performance of membrane manufactured by batch system was varied with organic solvent, monomer concentration, dipping time, heat treatment temperature, acid acceptor, ethanol post treatment, and acid post treatment. Ethanol post treatment was the most dominant factors in increasing permeate amount, while the monomer concentration and dipping time were the main factors in increasing selectivity. The spiral-wound module was produced with the membrane prepared at optimum condition of the continuous process. Comparing the performance of this membrane module made here with that of commercial membrane module, the permeate flux was increased by 33% while the rejection was decreased by 5%.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.305-311
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• 2019

The acrylic copolymer was designed and prepared for soft lens with high content. The copolymers were prepared using 2-hydroxyethyl methacrylate(HEMA) as a monomer and ethylene glycol dimethacrylate(EGDMA), glycerol dimethacrylate(GD), or glycerol 1,3-diglycerolate diacrylate (GDD) as a cross linking agent. The water content for high water content lens was 46%, which was higher compared to general purpose of 36%. The contact angle decreased from 38.6 to 34.4, which appears hydrophilic surface. The tensile strength decreased from 0.1 Mpato 0.08, then again to 0.05 as hydrophilic properties of cross linking agents increased. No phase separation was observed in the cross section of lens using scanning electron microscope. The real-time infrared technique was used in photo-polymerization. The initial polymerization rate increased from 0.6 to 0.9, depending on crosslinking agent.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.2
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• pp.189-198
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• 2009

As a part of an effort to minimize the polymerization shrinkage which is considered to be a major cause of failed bonds to tooth, newly designed 'Double LED system' was tested in the present study. Analyses were performed on the pattern of micro-leakage and the changes of strain which have occurred during the polymerization process. The results can be summarized as follows: 1. In the strain change, dramatic increase was observed with initiation of polymerization which was followed by subsequent gradual decrease with elapse of time in both the single LED system and double LED system. 2. The single LED system were shown to develop and maintain the maximum stress more than double LED system(p<0.05). 3. Less micro-leakage was found in the double LED system than in the single LED system(p<0.05). From the above-mentioned results, the double LED system can be a very useful tool in a sense of reducing polymerization shrinkage when compared to the single LED system. However, practical problems such as size of curing unit and its application method with its light intensity should be solved before its clinical application.

• Applied Chemistry for Engineering
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• v.29 no.3
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• pp.330-335
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• 2018

A new approach for the fabrication of organic-organic conducting composite thin films using simultaneous co-vaporization vapor phase polymerization (SC-VPP) of two or more monomers that have different polymerization mechanisms (i.e., oxidation-coupling polymerization and radical polymerization) was reported for the first time. In this study, a PEDOT-PSMA composite thin film consisting of poly(3,4-ethylenedioxythiophene)(PEDOT) and poly(styrene-co-maleic anhydride)(PSMA) was prepared by SC-VPP process. The preparation of organic-organic conductive composite thin films was confirmed through FT-IR and $^1H-NMR$ analyses. The surface morphology analysis showed that the surface of PEDOT-PSMA thin film was rougher than that of PEDOT thin film. Therefore, PEDOT-PSMA exhibited lower electrical conductivity than that of PEDOT. But the conductivity can be improved by adding 2-ethyl-4-methyl imidazole as a weak base. The contact angle of PEDOT-PSMA was about $50^{\circ}$, as compared to $62^{\circ}$ for PEDOT. The demonstrated methodology for preparing an organic-organic conductive hybrid thin film is expected to be useful for adjusting intrinsic conductive polymer (ICP)'s surface properties such as mechanical, optical, and roughness properties.