• Macromolecular Research
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• 제16권2호
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• pp.120-127
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• 2008

Glycidyl methacrylate linked poly(dimethylsiloxane) (GMA-PDMS) was synthesized and used as a stabilizer for the dispersion polymerization of methyl methacrylate (MMA) in supercritical $CO_2$. This study examined the effect of the concentrations of the stabilizer, 2,2'-azobisisobutyronitrile (AIBN) initiator, and MMA on the yield, molecular weight, and morphology of the poly(methyl methacrylate) (PMMA) product. PMMA was obtained in 94,6% yield using only 0,87 wt% GMA-PDMS, When the AIBN concentration was increased from 025 to 1.06 wt%, the molecular weight and particle size of the PMMA decreased from 56,600 to 21,600 and from 4.1 to $2.7{\mu}m$, whereas the particle size distribution increased from 1.3 to 1.9. The $M_n$ of the PMMA product ranged from 41,600 and 55,800 under typical polymerization conditions. The PMMA particle diameter ranged from 1.8 to $11.0{\mu}m$ and the particle size distribution ranged from 1.4 to 1.8.

• 도시과학
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• 제9권2호
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• pp.45-50
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• 2020

The formation characteristics of calcium carbonates are closely related to the durability and mechanical properties of cement-based materials. In this regard, a deep understanding of the reaction pathway of calcium carbonates is critical. Recently, non-classical nucleation theory was summarized and it was presumed that prenucleation clusters are present. The formation of the prenucleation cluster at undersaturated condition (≈ 0.1 ml) in the present study was investigated via electrical characteristics of an electrolytic solution. Calcium chloride dihydrate (CaCl2·2H2O) and sodium carbonate (Na2CO3) were used as starting materials to supply calcium and carbonate sources, respectively. Furthermore, the reaction pathway of calcium carbonates was investigated by time-resolved polarization and depolarization characteristics of the electrolytic solution. The time-resolved polarization and depolarization tests were conducted by switching polarity with an interval of 20 seconds for 1 hr and by measuring the variation of electrical resistance. It can be inferred from the results obtained in the present study that the reactive constituent for the formation of calcium carbonates was mostly consumed in the period possibly associated with the prenucleation and the reaction pathways may be governed by the monomer-addition mechanism.

• Elastomers and Composites
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• 제56권1호
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• pp.6-11
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• 2021

In order to develop an ultra-high-density elastomeric material for substitution of steel dynamic dampers, a new curing system and technique for high-loading of the filler were examined in this study. Mechanochemical modification of chloroprene rubber (MAH-g-CR) using an internal mixer was carried out with maleic anhydride (MAH) as a reactive monomer. The optimum amount of MAH was 10 phr and the efficient grafting of MAH on CR could be achieved at a mixing temperature of 100℃. After preparing MAH-g-CR, 50 mol% epoxidized natural rubber (ENR 50) was blended with MAH-g-CR to develop a "self-curable rubber blend system" via reaction between the functional groups of the elastomeric matrices without the curing agent and additives. The content of ENR 50 was fixed at 30 wt.% throughout evaluation of the curing behavior of the MAH-g-CR/ENR blend. Tungsten powder was added to the MAH-g-CR/ENR matrix up to 60 vol.% to obtain ultra-high-density, and the maximum density obtained was 7.57 g/㎤. Stable ts2 (scorch time) and t90 (90% cure time) could be obtained even when tungsten powder was incorporated up to 60 vol.%. In addition, the tensile strength and damping properties of MAH-g-CR/ENR containing 60 vol.% of tungsten were better than those of CR containing 60 vol.% of tungsten.

• 공업화학
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• 제25권3호
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• pp.318-323
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• 2014

랜덤 폴리프로필렌(random polypropylene, rPP)의 무수말레인산(maleic anhydride, MAH) 반응압출에 대한 MAH 함량 및 스티렌/MAH 몰비의 영향을 고찰하기 위해 이축압출기(twin screw extruder)를 이용하여 MAH가 그라프트된 rPP(MAH-g-rPP)를 제조하였다. MAH의 함량은 0.5, 1.0, 3.0, 5.0 phr이었고, 스티렌/MAH 몰비는 0, 1, 2로 하였으며, 개시제로는 dicumyl peroxide (DCP)가 사용되었다. MAH의 그라프트 정도는 FT-IR을 이용하여 $1700cm^{-1}$ 근처에서 나타나는 카르보닐기(C = O) 신축진동 피크의 존재 여부를 통해 확인하였으며, $3000cm^{-1}$ 근처의 C-H 신축진동을 기준으로 하여 정량한 결과 그라프트 반응이 MAH 함량이 3.0 phr까지 증가하는 경향을 보여주었고, 스티렌 몰비는 1.0일 때 최적을 나타내었다. MAH-g-rPP와 MAH-g-rPP가 5.0 phr 포함된 PP/MAH-g-rPP/pulp 복합체의 열적특성, 결정화 특성 등을 시차주사열용량분석기(DSC), 열중량분석기(TGA), X-선 회절분석(XRD), 편광현미경(POM) 등을 이용하여 관찰하였다. 비등온 결정화온도는 rPP-g-MAH가 첨가되었을 때 감소하는 경향을 나타내었고, PP/MAH-g-rPP/pulp 복합체의 인장특성과 인장시험 후 파단면의 SEM을 측정한 결과, MAH 함량 1.0 wt%, 스티렌/MAH 몰비 1.0일 때 상용화제로의 역할이 가장 우수한 것으로 나타났다. 복합체의 가공성 비교를 위해 복소 점도와 전단박하(shear thinning) 정도를 동적유변측정기를 이용하여 측정하였다. 상용화제를 가지는 복합체의 경우 낮은 멱수 법칙 지수(n)를 보여주었다.

• Fibers and Polymers
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• 제2권3호
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• pp.122-128
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• 2001

UV-curable polyurethane acrylate prepolymers were prepared from diisocyanates [isophorone diisocyanate (IPDI), 2,4-toluene diisocyanate (TDI), or 4,4'-dicyclohexylmethane diisocyanate (H$_{12}$MDI)], diols [ethylene glycol (EG), 1,4-butane diol (BD), or 1,6-hexane diol (HD)], polypropylene glycol as a polyol. UY-curable mixtures were formulated from the prepolymer (90 wt%), reactive diluent monomer trimethylol propane triacrylate (10 wt%). and photoinitiator 1-hydroxycy-clohexyl ketone (3 wt% based on prepolymer/diluent). The effects of different diisocyanates/low molecular weigh dial on the dynamic mechanical thermal properties and elastic recovery of UV-cured polyurethane acrylate films were examined. The tensile storage modulus increased a little in the order of EG > BD > HD at the same diisocyanate. Two loss modulus peaks for all samples are observed owing to the glads transition of softs segments ($T_gh$) and the glass transition temperature of hard segments ($T_gh$). For the same diisocyanate, $T_gh$, decreased, however, $T_gh$ increased, in the order of HD > BD > EG. The elastic recovery also increased in the order of HD > BD > EG at the same diisocyanate. In case of same diols, $T_gh$ increased in the order of $H_12$MDl > TDI > IPDI significantly. The ultimate elongation and elastic recovery increased in the order of TDI > IPDI > $H_12$MDl at the same diol.l.

• 한국치위생학회지
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• 제14권5호
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• pp.775-781
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• 2014

Objectives : The purpose of the study is to investigate the protective effect of coenzyme $Q_{10}$ on cytotoxicity effect of dental monomers in odontoblast(MDPC-23). Methods : MDPC-23 was incubated with the(co)monomers triethylene glycol dimethacrylate (TEGDMA) with and without addition of coenzyme $Q_{10}$. The cell proliferation and survival was determined using WST-1 assay. The level of reactive oxygen species(ROS) was measured by immunofluorescent staining for DCF-DA. Results : TEGDMA treatment decreased the cell proliferation by dose dependently(0.1, 1, 2.5, 5, 10 mM) on the growth of MDPC-23 cells. Coenzyme $Q_{10}$ showed cell proliferation from 5 to $500{\mu}M$ by WST-1 assay. Pre-treatment coenzyme $Q_{10}$ showed the antioxidant effect on proliferation and viability of MDPC-23 after 48h(p<0.05). The positive cells were observed in non-coenyme $Q_{10}$ treatment group(group 2) in comparison with coenyme $Q_{10}$ pre-treatment group(group 1) by DCF-DA. The fluorescence positive cells showed 14.715(group 1) and 19.788(group 2) using image J system. Conclusions : TEGDMA induced cytotoxicity. The MDPC-23 cell death was associated with the increasing ROS. Coenyme $Q_{10}$ showed the antioxidant effects by decreasing ROS. This effects may contribute to the treatment of periodontal disease induced by TEGDMA after operation.

• 청정기술
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• 제23권2호
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• pp.148-157
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• 2017

To prepare UV-curable polyurethane-acrylate oligomer, NCO-terminated urethane prepolymers with trimethylolpropane, [TMP; 0 (0), 0.1 (0.021) and 0.2 (0.043) mole (mole fraction)] as crosslinkable tri-functional chain extender were end-capped with pentaerythritol triacrylate [PETA; 2.0 (0.400), 1.7 (0.354) and 1.4 (0.304) mole (mole fraction)] with one hydroxyl group/three vinyl functionalities. The stable as-formulated UV-curable polyurethane-acrylates [stable mixtures of PETA-capped oligomer/reactive acrylic monomer diluents without/with heptadecafluorodecyl methacrylate (PFA; 0, 6 and 9 wt%)] were formed up to 0.2 (0.043) mole (mole fraction) of TMP content in the prepolymer, while homogeneous-mixing failed at 0.3 (0.068) mole (mole fraction), in which the crosslink density in NCO-terminated urethane prepolymer was too high to enable the formation of stable mixture. This study examined the effect of TMP/PETA molar ratio and heptadecafluorodecyl methacrylate (PFA) content (wt%) on the properties of UV-cured polyurethane-acrylates as marine antifouling coating materials. The properties of UV-cured polyurethane-acrylate were found to be significantly dependent on the crosslinkable TMP/PETA ratio and PFA content. With the increasing of the TMP and PFA contents, the contact angles increased, and consequently the surface tension decreased. The adhesion of algae/barnacles to PFA contained film samples were found to be sufficiently weak to allow their easy removal. These results suggest that the UV-cured samples containing PFA have strong potential as coating materials for antifouling applications.

• Molecules and Cells
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• 제19권1호
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• pp.97-103
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• 2005

The role of residue C323 in catalysis by human glutamate dehydrogenase isozymes (hGDH1 and hGDH2) was examined by substituting Arg, Gly, Leu, Met, or Tyr at C323 by cassette mutagenesis using synthetic human GDH isozyme genes. As a result, the $K_m$ of the enzyme for NADH and ${\alpha}-ketoglutarate$ increased up to 1.6-fold and 1.1-fold, respectively. It seems likely that C323 is not responsible for substrate-binding or coenzyme-binding. The efficiency ($k_{cat}/K_m$) of the mutant enzymes was only 11-14% of that of the wild-type isozymes, mainly due to a decrease in $k_{cat}$ values. There was a linear relationship between incorporation of [$^{14}C$]p-chloromercuribenzoic acid and loss of enzyme activity that extrapolated to a stoichiometry of one mol of [$^{14}C$] incorporated per mol of monomer for wild type hGDHs. No incorporation of [$^{14}C$]p-chloromercuribenzoic acid was observed with the C323 mutants. ADP and GTP had no effect on the binding of p-chloromercuribenzoic acid, suggesting that C323 is not directly involved in allosteric regulation. There were no differences between the two hGDH isozymes in sensitivities to mutagenesis at C323. Our results suggest that C323 plays an important role in catalysis by human GDH isozymes.

• Elastomers and Composites
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• 제40권1호
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• pp.53-58
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• 2005

사염화탄소는 C-Cl결합이 끊어진 후에 생성되는 삼염화탄소 라디칼의 공명 안정성에 의해 매우 반응성이 높은 사슬이동제로 알려져 있으며, 본 논문은 벤질 라디칼과 삼염화탄소 라디칼의 안정성을 비교연구하였다. 큐밀클로라이드는 C-Cl결합이 끊어진 후에 벤질 라디칼을 생성하므로 이 연구에 적합한 구조이다. 큐밀클로라이드와 사염화탄소의 반응성은 스티렌을 단량체로 한 자유라디칼 중합을 통해 계산된 사슬 이동 상수로 비교하였다. 실험 결과에 따르면 큐밀클로라이드는 사염화탄소보다 더 반응성이 높았다. 계산된 큐밀클로라이드의 스티렌에 대한 사슬이동상수 값이 약 0.0463으로 0.0011인 사염화탄소 보다 훨씬 높았다. 이 결과는 벤질 라디칼이 삼염화탄소 라디칼보다 훨씬 높은 안정성을 보여주기 때문인 것으로 추정된다. 큐밀클로라이드의 사슬이동상수의 유효성을 조사하기 위하여 Monte Carlo 모의 실험방법을 사용하였다.

• Restorative Dentistry and Endodontics
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• 제20권1호
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• pp.33-54
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• 1995

The degree of conversion of composite resin was known to have influence on the mechanical properties of composite materials such as hardness, strength, wear resisitance, dimensional and color stability. Also unreacted monomer was reported to be harmful to the pulp. So the degree of conversion was a very important factor in the success of composite resin restorations. In recent, the dual cure resin cement was developed with the advocations that it could increase the curing rates in the sites where the curing ligt could not reach. Moreover many manufactors added some adhesive components in the resin cement. This study was undertaken to observe the effects of curing depth and light curing times on the degree of conversion of dual cure resin cements. CR INLAY CEMENT, DUAL CEMENT and OPTEC BOND, by the Fourier transform Infrared analysis, changing the curing depth 1mm, 2mm and 3mm, and varying the light curing time 20 seconds, 40 seconds and 80 seconds at each depth. The cytotoxicity of dual cure resin cements was tested by the in vitro MTT method using L929 cell. The results was evaluated and compared statistically. The results were obtained as follows : 1. The dual cure resin cements reavealed various degree of conversion, CR INLAY CEMENT and DUAL CEMENT had a tendency to be more reactive to the light cure and OPTEC BOND was a more chemical one. 2. CR INLAY CEMENT and DUAL CEMENT showed the lowest degree of conversion in 2 mm depth, and in 3mm depth the degree of conversion increased, which were due to the chemical cure of dual cures, but OPTEC BOND showed decreasing degree of conversion with increasing curing dept h and all experimental groups showed lower degree of conversion than CHEMICAL group which cured in dark room with no light, so the weak light-curing of dual cure resin cement prevented the chemical cure. (P<0.05) 3. CR INLAY CEMENT and DUAL CEMENT showed increasing degree of conversion in 1 mm and 3 mm, according to the increasing cure times, but in 2 mm depth the degree of conversion decreased with increasing light-curing times and OPTEC BOND showed contrary tendency, but there was no ststistical importance in the differences among the experimental group.(P>0.05) 4. The optical density by MTT assay of extractions of CR INLAY CEMENT, DUAL CEMENT and OPTEC BOND revealed no statitically important differences comparing with optical density of negative control.(P>0.05) 5. CR INLAY CEMENT showed a tendency of increaing cytotoxicity with days and DUAL CEMENT and OPTEC BOND showed higher cytotoxicity in 2 days than in 4 days, but there was no statistical importance in the differences.(P>0.05).