• Bulletin of the Korean Chemical Society
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• v.21 no.9
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• pp.896-900
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• 2000

A study was done on the synthesis of new poly(arylene ether)s and poly(arylenesulfide) with rigid benzoxazole pendants using nucleophilic aromatic substitution reaction. As a new aromatic monomer, 1,4-bis(2-benzox-azolyl)-2,5-difluorobenzene [I] w as synthesized in three steps starting from 1,4-dibromo-2,5-difluorobenzene. A model reaction of difluoro monomer [I] with two equivalents of m-cresol or thiophenol in a typical ether con-densation reaction conditions gave very high yields ( > 93%) of the desired disubstituted product, suggesting the feasibility of polymer formation in these reaction system. Monomer[I] was polymerized with bisphenols and bisbenzenethiol in NMP using K2CO3 as base. The molecular weight of the resulting polymers, however,seemed relatively low according to their solution viscosity values ( ηinh = 0.15-0.29 dL/g). The poly(arylene ether)s were soluble in several common organic solvents including chloroform, pyridine and N,N'-dimethylfor-mamide. The poly(arylene sulfide) was, however, ony soluble in strong acids like sulfuric acid and trifluoro-acetic acid. The glass transition temperatures were found to be 175-215 $^{\circ}C.$ These polymers were stable up to 380-420 $^{\circ}C$ in both nitrogen and air, as determined by the temperature that a significant weight loss began to appear on TGA.

• Elastomers and Composites
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• v.56 no.3
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• pp.152-163
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• 2021

Liquid butadiene rubber (LqBR) is used as a processing aid and plays a vital role in the manufacture of high-performance tire tread compounds. In this study, center-functionalized LqBR (C-LqBR) was polymerized with different vinyl content via anionic polymerization. The effects of the vinyl content on the properties of the compounds were investigated by partially replacing the treated distillate aromatic extract (TDAE) oil with C-LqBR in silica-filled rubber compounds. C-LqBR compounds showed a low Payne effect and Mooney viscosity regardless of the vinyl content, because of improved silica dispersion due to the ethoxysilyl group. As the vinyl content of C-LqBR increased, the optimum cure time (t₉₀) increased owing to a decrease in the number of allylic hydrogen. Moreover, the glass transition temperature (T_g) of the compound increased, and snow traction and abrasion resistance performance decreased, whereas wet grip improved. The energy loss characteristics revealed that the hysteresis attributed to the free chain ends of C-LqBR was dominant.

• Elastomers and Composites
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• v.53 no.4
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• pp.202-206
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• 2018

Five solution styrene butadiene rubber/neodymium butadiene rubber (SSBR/NdBR) composites were manufactured using different ratios of SSBR and NdBR. In this study, the composites were reinforced with NdBR and silica to confirm the physical properties of SSBR used for treads of automobile tires and the dispersibility with silica. The morphologies of the rubber composites were observed using field-emission scanning electron microscopy (FE-SEM). The crosslinking behaviors of the composites were tested using a rubber process analyzer (RPA), and the abrasion resistances were tested using a National Bureau of Standards (NBS) abrasion tester. The hardness values, tensile strengths, and cold resistances of the composites were also tested according to ASTM standards. Increased NdBR content yielded composites with excellent crosslinking properties, abrasion resistances, hardnesses, tensile strengths, and cold resistances. The crosslinking point increased due to the double bond in NdBR, thereby increasing the degree of crosslinking in the composites. The NdBR-reinforced composites exhibited excellent abrasion resistances, which is explained as follows. In SSBR, a breakage is permanent because a resonance structure between styrene and SSBR forms when the molecular backbone is broken during the abrasion process. However, NdBR forms an additional crosslink due to the breakdown of the molecular backbone and high reactivity of the radicals produced. In addition, the low glass transition temperature (Tg) of NdBR provided the rubber composites with excellent cold resistances.

• Korean Journal of Materials Research
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• v.31 no.8
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• pp.445-449
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• 2021

Zintl compound Mg₃Sb₂ is a promising candidate for efficient thermoelectric material due to its small band gap energy and characteristic electron-crystal phonon-glass behavior. Furthermore, this compound enables fine tuning of carrier concentration via chemical doping for optimizing thermoelectric performance. In this study, nominal compositions of Mg_3.8Sb_2-xTe_x (0 ≤ x ≤ 0.03) are synthesized through controlled melting and subsequent vacuum hot pressing method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are carried out to investigate phase development and surface morphology during the process. It should be noted that 16 at. % of excessive Mg must be added to the system to compensate for the loss of Mg during melting process. Herein, thermoelectric properties such as Seebeck coefficient, electrical conductivity, and thermal conductivity are evaluated from low to high temperature regimes. The results show that Te substitution at Sb sites effectively tunes the majority carriers from holes to electrons, resulting in a transition from p to n-type. At 873 K, a peak ZT value of 0.27 is found for the specimen Mg_3.8Sb_1.99Te_0.01, indicating an improved ZT value over the intrinsic value.

• Journal of Korean Ophthalmic Optics Society
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• v.8 no.1
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• pp.17-22
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• 2003

The experimental FT-IR spectra and DTA curves of the $PbO-Bi_2O_3-B_2O_3-SiO_2$ glasses have been investigated. The composition ratio dependence of glass transition temperature showed that the structure of this glass system changes at 60 mol% $Bi_2O_3$. We have observed that the FT-IR spectra of the investigated samples with high bismuth content are dominated by bands associated to the structural units of the heaviest cation, $Bi^{3+}$ and the boron atoms in the treated samples are three and four coordinated even for very high $Bi_2O_3$ content. The low intensity of these non-bridging oxygen bands, for high PbO content glasses, can be attributed to the strong network-forming roles of PbO. The glasses absorption bands exhibited a greater change in intensities on crystallization.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.

• Korean Journal of Materials Research
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• v.4 no.1
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• pp.90-96
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• 1994

ZnO thin films were deposited using Diethylzinc and $N_{2}O$ gas by plasma enhanced CVD (PECVD) at low substrate temperatures below $300^{\circ}C$. The effect of deposition parameters on the growth rate and the structural properties was determined at various deposition conditions. Crystallized ZnO thin films were successfully deposited even at $150^{\circ}C$ of substrate temperature. Above $200^{\circ}C$ c-axis oriented ZnO thin films, of which a standard deviation of X-ray rocking curve was less than $6^{\circ}$. were deposited on glass substrates. The variation of deposition rate showed different trends depending on substrate temperature and rf-input power. According to the deposition rate behavior as a function of substrate temperature, the transition points were observed resulting from crystallization of ZnO thin films. The activation energies for the deposition of ZnO thin films were 3.1KJ/mol and 1.9KJ/mol for the rf powers of 200W and 250W, respectively.

• Composites Research
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• v.17 no.1
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• pp.10-17
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• 2004

In this work, the blend system prepared from epoky(DGEBA)/polymethylmethacrylate(PMMA) was investigated in thermal and mechanical interfacial property measurements. The thermal properties were carried out by DSC, DMA, and TGA measurements. Also, the surface free energy and fracture toughness were determined by contact angle and critical stress intensity factor($K_{IC}$), respectively. And the fracture surface was observed by SEM after $K_{IC}$ tests. As experimental results, the curing temperature and glass transition temperature were slightly increased in addition of PMMA. Surface free energy of the blends showed an improved value at low contents of PMMA which could be attributed to the both increasings of London dispersive and polar components. From measurement of $K_{IC}$ of the blends, the highest value was found at 5 phr. This was due to the increasing of compatibility or physical interaction in macromolecular chains between DGEBA and PMMA of the blends.

• Elastomers and Composites
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• v.43 no.2
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• pp.82-87
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• 2008

In this study, nine kinds of polyimides were synthesized from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA), m-pheny lenediamine (m-PDA) and 4,4'-oxydianiline (ODA) by controlling molar ratio of monomers. Synthesized polyimides were used as insulator films for 2-layer Flexible Copper Clad Laminate(FCCL) which were manufactured by the casting method. Glass transition temperature and thermal degradation temperature for 5% weight loss of the polyimide film were improved by increasing contents of m-PDA and PMDA, respectively. Water absorption of polyimide film was reduced by increasing contents of ODA and BPADA which have relatively long structure, respectively. Peel strength of 2-layer FCCL was improved by increasing contents of ODA and BPADA.

• Polymer(Korea)
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• v.34 no.3
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• pp.191-197
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• 2010

To improve the curing method of anisotropic conductive film (ACF) at low temperature, it was studied to replace the thermal latent curing agent of imidazole compounds by the curing agent of cationically initiating type. Thermo-mechanical properties such as glass transition temperature, storage modulus, and coefficient of thermal expansion were investigated for the analysis of curing behavior. The reliability of ACF were observed in thermal cycle and high temperature-high humidity test. ACF using cationic initiator showed faster curing, lower CTE, and higher $T_g$ than the case of using imidazole curing agent, which is important for the high temperature stability. Furthermore, ACF using cationic initiator maintained a stable contact resistance in reliability test, although it was cured at low temperature and fast rate. With these results, it was confirmed that the curing method of epoxy had great effect on thermo-mechanical properties and reliability of ACF.