• Polymer(Korea)
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• v.38 no.5
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• pp.566-572
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• 2014

Maleic anhydride (MAH) grafted polypropylenes (PP) (MAH-g-PP) were prepared by changing MAH content and styrene monomer (SM)/MAH mole ratio with different type PP, using a twin screw extruder. The types of PP were isotatic PP (iPP), block PP (bPP), and random PP (rPP) and dicumyl peroxide (DCP) was used as an initiator. The graft degree of MAH was confirmed by the existence of carbonyl group (C=O) stretching peak at $3100cm^{-1}$ of FTIR spectrum. Thermal properties of MAH-g-PP and PP/MAH-g-PP/pulp composites were investigated by DSC and TGA. There was no district change in thermal properties of PP/MAH-g-PP/pulp composites. Based on tensile properties and SEM pictures for fractured surface of PP/MAH-g-PP/pulp composites, MAH-g-rPP was the best as the compatibilizer and optimum formulation was MAH content of 1.0 wt%, SM/MAH mole ratio of 1.0, and melt index (MI) of 25 g/10 min. The rheological properties of the composites were investigated by a dynamic rheometer. The complex viscosity, shear thinning effect, and water uptake incresed with pulp content.

• Journal of Adhesion and Interface
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• v.17 no.3
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• pp.110-116
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• 2016

A decrease in the retro-reflectivity of glass-bead-covered road paint because of a rainwater film significantly reduces the visibility of drivers at night, and has been considered as a critical cause of traffic accidents. For enhanced visibility, the microencapsulation of hydrophobically modified $SrAl_2O_4:Eu^{2+}$,$Dy^{3+}$ phosphorescent phosphor was carried out via suspension polymerization of methyl methacrylate (MMA). The effects of surface modification agent and radical initiator types, loading amount of phosphorescent phosphor, and microcapsule size on the phosphor content ($W_{TGA}$) in the luminous poly(methyl methacrylate) (PMMA) microcapsules were investigated by thermogravimetric analyses (TGA). It was found that the $W_{TGA}$ value was ranged from 7 wt% to 81 wt%, which suggests suspension polymerization is suitable for the preparation of luminous microcapsules with a wide range of phosphor content. At a lower loading amount of phosphor, the $W_{TGA}$ value obviously increased as the microcapsule size decreased; however, the $W_{TGA}$ values with a higher loading amount of phosphor were less affected by the microcapsule size. The luminous microcapsules with the size range of $425{\sim}710{\mu}m$ were collected and tested as a luminous road lanes. It was found that luminance intensities of the microcapsule-coated plates remained higher than $300mcd/m^2$ for up to 100 s in darkness after 20 min of light emitting diode lamp irradiation. The results suggest that the luminous microcapsules can be a candidate for the replacement of glass beads for enhanced visibility of drivers.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.127-134
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• 2015

Aluminum nitride (AlN) single crystals have attracted much attention for a next-generation semiconductor application because of wide bandgap (6.2 eV), high thermal conductivity ($285W/m{\cdot}K$), high electrical resistivity (${\geq}10^{14}{\Omega}{\cdot}cm$), and high mechanical strength. The bulk AlN single crystals or thin film templates have been mainly grown by PVT (sublimation) method, flux method, solution growth method, and hydride vapor phase epitaxy (HVPE) method. Since AlN suffers difficulty in commercialization due to the defects that occur during single crystal growth, crystalline quality improvement via defects analyses is necessary. Etch pit density (EPD) analysis showed that the growth misorientations and the defects in the AlN surface exist. Transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) analyses were employed to investigate the overall crystalline quality and various kinds of defects. TEM studies show that the morphology of the AlN is clearly influenced by stacking fault, dislocation, second phase, etc. In addition EBSD analysis also showed that the zinc blende polymorph of AlN exists as a growth defects resulting in dislocation initiator.

• Elastomers and Composites
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• v.44 no.3
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• pp.336-342
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• 2009

We measured shear viscosity of polystyrene (PS) and poly(butyl methacrylate) (PBMA) particles, with a capillary rheometer, prepared by suspension polymerization with 1.0 wt% hydrophobic silica as a stabilizer by varying the initiator concentration at $75^{\circ}C$. PS particles with weight average molecular weight of 66,500 g/mol displayed a Newtonian behaior at low shear rates at $190^{\circ}C$. With increasing molecular weight, PS particles showed shear thinning over the entire range of shear rates. For PBMA particles, steady shear measurement was carried out at $170^{\circ}C$. PBMA particles with weight average molecular weight of 156,700 g/mol showed a Newtonian behaior only at low shear rates. PBMA particles also showed shear thinning with an increase in molecular weight and its pattern similar to that of PS. When carbon black was incorporated into PS and PBMA polymers, steady shear measurement was conducted at $170^{\circ}C$. An increase in carbon black concentration in PS and PBMA composite particles exhibited a progressive increase in shear viscosity. The increase in shear viscosity, however, was less pronounced compared to an increase as a function of molecular weight. Preparing PS composites containing carbon black by internal mixing resulted in an increase in shear viscosity. Its increase, however, was found to be less than that shown in PS composite particles. We speculate that this is caused by an enhanced dispersion of carbon black particles with an internal mixer. Yield behavior was not observed in any of the samples we selected in this experiment.

• The Korean Journal of Zoology
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• v.39 no.4
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• pp.378-386
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• 1996

We have developed a couple of new luciferase reporter plasmida with very low background reporter actlvltlea. One can be used to measure the promoter strength, after insertion of some promoter fragment into the reporter plasmid, and the other, with very low basal promoter actlvltlea, allis In studying eukaryotic transcriptional regulators. The latter reporter plasmid contains such cli elements as a 17 nucleotide long inftlator, Spl.blndIng sftes, GAL4 binding sltea, and bInding sitea for a certain Drosophila homeodomain proteins. In an attempt to construct an improved reporter plaimid by fadlltating transcriptional termination and minimizing any interference by cryptic promoters which may be preaent in the reporter pleamld DNA, we have inserted transsrlptional termination-related signals, a three tandem repeat of SV4O polyadenylatlon signal (AAA) and the putative transcrtptional termination signal (UMS) of the mouse c-mos gene, Into just upstream of the initIator, and the promoter actlvitiea were measured by a transIent expression assay employing the Drosophila Schneider line 2 cells. As expected, the basal promoter activitIes decreased maximally when both transcription termination related elements were inserted. Moreover, the reporter plasmld with the two elements allowed more sensitive measurement of transcriptional activation than the reporter piasmid without them. Theae reporter plasmids can be used for studying transcriptional regulators of higher organisms Including mammals as well as Droiophlla melanogaiter.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.27 no.6
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• pp.528-534
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• 2005

Angiogenesis is important for the growth and metastasis of solid tumors. Some growth factors, inflammatory cytokines, and angiogenin are known to promote tumor angiogenesis. Among them, Vascular endothelial growth factor (VEGF) is the most intriguing factor in regard to tumor angiogenesis. Inhibition of VEGF activity by neutralizing antibodies or by the introduction of dominant negative VEGF receptors into endothelial cells of tumor-associated blood vessels resulted in the inhibition of tumor growth and in tumor regression, indicating that VEGF is a major initiator of tumor angiogenesis. VEGF promotes angiogenesis through their receptors, Flt-1 and Flk-1/KDR. on vascular endothelial cells. These two receptors were usually believed to be expressed specifically on vascular endothelial cell. Several reports have now shown that VEGF is not only significantly associated with microvessel density but also has prognostic value in both node-negative and node-positive oral squamous cell carcinoma. For many years several histologic features of the neoplasms are being considered when assessing the influence of malignancy grading on recurrence and prognosis. Among the characteristics investigated, degree of keratinization, nuclear pleomorphism, mode of invasion, microscopic depth of invasion, intravascular invasion, lymphocyte infiltration, and number of mitoses have been considered as important prognostic factors. So, this study was conducted to evaluate the correlation of vascular endothelial growth factor expression with malignancy in paraffin-embedded biopsy specimens from 11 patients with tongue cancers. Our results showed that high immunoreactivity specimens of VEGF expression were significantly lower keratinization degree and more pronounced nuclear pleomorphism than in low immunoreactivity specimens. Thus, VEGF expression could be used as a prognostic marker in tongue cancer.

• Korean Journal of Agricultural Science
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• v.32 no.1
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• pp.19-27
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• 2005

This study was performed to evaluate the physical and mechanical properties of polymer concrete using unsaturated polyester resin, initiator, heavy calcium carbonate, crushed gravel, recycled coarse aggregate, silica sand and recycled fine aggregate. The unit weight, compressive strength, flexural strength and dynamic modulus of elasticity were decreased with increasing the content of recycled aggregate. The unit weight, compressive strength, flexural strength and dynamic modulus of elasticity were showed in $2,127{\sim}2,239kg/m^3$, 80.5~88.3MPa, 19.2~21.5MPa and $254{\times}10^2{\sim}288{\times}10^2MPa$ at the curing age 7 days, respectively. Therefore, these recycled aggregate can be used for polymer concrete.

• Polymer(Korea)
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• v.33 no.4
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• pp.358-363
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• 2009

Maleic anhydride-grafted polypropylene has been widely used to improve the interfacial interaction between the components in PP/polar polymer blends and PP/filler composites and to maximize the physical properties and thermal properties. In this paper. the maleic anhydride (MAH)-grafted polypropylene (co-PP) was fabricated through reactive extrusion process with di-cumyl peroxide (DCP) as an initiator. The grafting degree of MAH depending on the contents of DCP and MAH was investigated by FT-IR spectra and chemical titration. The grafting degree increased with increasing MAH concentration and also showed maximum value at 0.06 wt% of DCP concentration. Melt flow index (MFI) of the grafted copolymer was increased with increasing the contents of MAH. The DSC and TGA analysis data indicate the melting temperature and thermal degradation of PP depending on the grafting degree of MAH.

• Polymer(Korea)
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• v.33 no.6
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• pp.608-614
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• 2009

The cation-exchange membrane which was sulfonated styrene-ethylene/buthlene-styrene(SEBS) block copolymer containing the high impact polystyrene (HIPS) was prepared via post-sulfonation and casting method using the epoxidized polybutadiene and divinylbenzene as crosslinking agents. Post-sulfonation was carried out with sulfuric acid as sulfonating agent and silver sulfate as initiator in the nitrogen atmosphere. The basic properties of membranes, degree of sulfonation (DS), water uptake, ion-exchange capacity (IEC), electrical resistance, and modulus have been examined. DS of membrane increased with increasing the sulfonation time. The maximum DS of membrane containing 10 wt% HIPS was 83.6 %. The water uptake and IEC of membranes gradually increased as increasing the DS. The maximum water uptake and IEC of membranes were 43.8 % and 1.14 meq/g, respectively. The lowest electrical resistance of membrane containing the 20 wt% HIPS was $83\;\Omega{\cdot}cm^2$. The electrical conductivity of membrane containing 10 wt% HIPS was $1.22\times10^{-4}S/cm$. The modulus of membrane increased with increasing DS and these values were 153 and $204\;kgf/cm^2$ before and after sulfonation, respectively.

• Polymer(Korea)
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• v.32 no.3
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• pp.276-283
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• 2008

Kind of monomer(MMA, EA, BA, St)and the monomer ratio(80/20 to 20/80) where changed in the preparation of the core shell binder, and property was improved the plasma processing. Each material changed by plasma treatment time($1{\sim}10\;s$) to change to measure the tensile strength, contact angle and adhesion peel strength for the core shell binder optimal conditions for handling the output of the surface treatment. The type of polymerization and composition of the binder is a regardless initiator of APS, the reaction temperature of $85^{\circ}C$ to 0.3 wt% of the surfactant used to indicate when the conversion rate was the highest, core shell composite particle binder got two glass temperature curves. Core shell binder after the plasma processing contact angle change is the PEA/PSt 38 percent of cases within five seconds to indicate slight decrease was a decline rapidly if not handled $0^{\circ}$ to reach. Tensile strength PSt/PMMA varies $46.71{\sim}46.27\;kg_f$/2.5 cm and adhesion strength PEA/PMMA varies $7.89{\sim}14.44\;kg_f$/2.5 cm increases. Overall, adhesion strength of core shell composite particle is in the order of order PEA>PBA>PSt for shell monomer MMA.