• Journal of the Korean Society of Clothing and Textiles
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• v.18 no.1
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• pp.15-22
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• 1994

The formation of carbonyl group was dominant to other functional groups. Concentrations of both carboxyl and peroxide groups were found to rapidly reach low steady state values that increased slightly with increa-sing temperature and relatice humidity. Since the deg-radation of cellulose samples was in the initial stage and the conversion of glycosidic bonds and hydroxyl groups were very small, it was found that changes in the physical and chemical properties could be fitted to a first-order reaction model.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.10a
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• pp.60-61
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• 1994

복합막은 기존의 비대칭막에 비해서 극히 얇은 표면층을 형성할 수 있다. 이러한 복합막은 배제율도 우수할 뿐만아니라 투과속도 또한 매우 큰 특징을 가지고 있으며, 해수의 담수화를 비롯하여 초순수 제조 등 각종 산업분야에서 많이 응용되고 있다. 우수한 분리막을 제조하기 위해서는 막의 표면층을 보다 더 치밀하고 얇게 형성할 수 있어야 한다. 이렇게 하기 위해서는 지지막 또한 매우 중요한 요인으로 작용한다. 표면층이 치밀하고, 가능한 한 porosity가 큰 지지막을 제조해야한다. 따라서 본 연구에서는 고분자 물질로 Polyethersulfone을 사용하여 지지막을 만들었다. 이 지지막위에 계면중합법으로 NF/RO용 복합막을 제조하였다. 높은 투과 속도 및 염의 배제율이 우수한 복합막을 제조하기 위해서 먼저 Polymer 농도, 첨가제 종류및 농도 등에 의한 각종 제막조건에 따른 지지막의 성능을 조사하였다. 여기에 Monomer 농도를 변화시켜서 계면중합으로 복합막을 제조하여 그 성능 변화를 측정하였다.

• Restorative Dentistry and Endodontics
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• v.32 no.1
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• pp.28-36
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• 2007

The purpose of this study was to compare the effect of exponential curing method with conventional curing and soft start curing method on polymerization shrinkage of composite resins. Three brands of composite resins (Synergy Duo Shade, Z250, Filtek Supreme) and three brands of light curing units (Spectrum 800, Elipar Highlight, Elipar Trilight) were used. 40 seconds curing time was given. The shrinkage was measured using linometer for 90 seconds. The effect of time on polymerization shrinkage was analysed by one-way ANOVA and the effect of curing modes and materials on polymerization shrinkage at the time of 90s were analysed by two-way ANOVA. The shrinkage ratios at the time of 20s to 90s were taken and analysed the same way. The results were as follows : 1. All the groups except Supreme shrank almost within 20s Supreme cured by soft start and exponential curing had no further shrinkage after 30s (p < 0.05). 2. Statistical analysis revealed that polymerization shrinkage varied among materials (p = 0.000) and curing modes (p = 0.003). There was no significant interaction between material and curing mode. 3. The groups cured by exponential curing showed the statistically lower polymerization shrinkage at 90s than the groups cured by conventional curing and soft start curing (p < 0.05). 4. The initial shrinkage ratios of soft start and exponential curing were statistically lower than conventional curing (p < 0.05). From this study, the use of low initial light intensities may reduce the polymerization rate and, as a result, reduce the stress of polymerization shrinkage.

• Proceedings of the Korean Fiber Society Conference
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• 1997.10a
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• pp.377-380
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• 1997

• Polymer(Korea)
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• v.25 no.1
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• pp.1-5
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• 2001

Monomer casting nylons were synthesized by casting anionic polymerization of ${\varepsilon}$-caprolactam. Polymerization rates, molecular weights of the products and the conversions were determined while varying the content of catalysts in the range of 0.2~0.6 mol% and 0.1~1.0 mol% for initiator. The polymerization rates were enhanced as the ratio of catalysts to initiator increased. The maximum molecular weight was observed when the ratio of catalysts to initiator was 0.8, and as the ratio increased the molecular weight decreased. On the other hand, when the ratio of catalysts to initiator was below 0.8, the conversions and the molecular weights were abruptly diminished due to the termination of growing chains.

• Journal of the Korean Chemical Society
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• v.27 no.4
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• pp.287-293
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• 1983

Free radical-initiated copolymerizations of diethyl ${\alpha}$-phenylvinyl phospbate (DEPVP) with acrylonitrile (AN) and maleic anhydride (MAnh) were studied. The monomer reactivity ratios for AN/DEPVP pair, determined at $70^{\circ}C$ in bulk using benzoyl peroxide as an initiator, were;$ r_1(AN) = 0.77, r_2(DEPVP) = 0.002$. The values of the Alfrey-Price constants, Q and e, for DEPVP were calculated to be 0.012 and -1.35, respectively. Free radical-initiated copolymerization of MAnh/DEPVP pair in chloroform at $70^{\circ}C$ produced 1 : 1 alternating copolymers regardless monomer feed composition with the highest copolymerization rate at the molar ratio of MAnh : DEPVP = 7 : 3. The equilibrium constant of a charge-transfer complex between DEPVP and MAnh in deutrated chloroform, determinated at room temperature by transformed Benesi-Hildebrand NMR method, was 0.085 l/mol. The reduced viscosity of copolymers of AN/DEPVP pair decreased as the content of DEPVP units increased, while that of MAnh/DEPVP pair remained more or less constant.

• Elastomers and Composites
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• v.33 no.4
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• pp.231-237
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• 1998

In order to investigate the physical properties of rubber blend compound, this experiment was carried out on the cure rate, loss tangent, reinforcement and abrasion properties of S-SBR (solution styrene-butadiene rubber) blends containing silane coupled silica and E-SBR (emulsion styrene-butadiene rubber) blends containing carbon black as a model compound. E-SBR blend showed the highest total bound rubber(TBR), while S-SBR blends showed constant TBR level regardless of rubber type. Rapid cure rate was achieved when the styrene and vinyl content of rubber microstructure decreased and TBR content of rubber compounds increased. The modulus as the index of rubber reinforcement showed the linear relation with TBR content. The large amount of PICO loss was observed when the styrene and vinyl content of rubber microstructure increased, while the small amount of PICO loss was observed when the ratio of bu-tadiene increased in the S-SBR blends with silane copuled silica. The high loss tangent at $0^{\circ}C$, the low loss tangent at $60^{\circ}C$, and the large difference of loss tangent were shown in the S-SBR blends with high styrene content compared to E-SBR blend.

• Journal of the Korean Chemical Society
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• v.23 no.4
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• pp.259-266
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• 1979

Linear polyethers were prepared by the reaction of diphenoxide anions from 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxylphenyl) sulfide, and bis (khydroxyphenyl) sulfone with 1,6-dibromohexane in aqueous/nitrobenzene heterogeneous phases. Tetrabutylammonium bromide was employed as a phase transfer catalyst. The polymerizations were dependent both on stirring speed and catalyst level, but only up to certain maximum values. Distribution studies demonstrated transference of diphenoxide anions from aqueous phase into nitrobenzene in the presence of the catalyst. Some of polymers were characterized with respect to their intrinsic viscosities (0.09-O.16), number average molecular weight (2400-4800)) and thermal properties. The use of a new terminology, 'phase transfer polymerization?, is proposed to differentiate this type of polymerizations from interfacial polycondensations.

• Elastomers and Composites
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• v.48 no.4
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• pp.294-299
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• 2013

Solution polymerization was conducted with water-soluble methacrylic acid (MAA) as a monomer and potassium persulfate (KPS) as an initiator at a selected temperature between $70^{\circ}C$ and $90^{\circ}C$. When the ratio between MAA and water was reduced or initiator concentration increased, molecular weights decreased. Molecular weights of poly(methacrylic acid) (PMAA) showed nearly no dependence on reaction temperature. The Weissenberg effect was observed in most polymerization reactions, while its effect weakened at $90^{\circ}C$. The polydispersity index was less than 1.5 in most of the reactions. An increase in the stirring speed produced PMAAs with increasing molecular weights. When the stirring speed reached 800 rpm, we retrieved a monodisperse PMAA with both the number and weight average molecular weights of 791,000 g/mol. The glass transition temperature was found to be $162^{\circ}C$.

• Polymer(Korea)
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• v.30 no.5
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• pp.437-444
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• 2006

Reactive hydroxypropyl methylcellulose phthalate (reactive HPMCP) was synthesized by using a stepwise urethane reaction with isophorone diisocyanate (IPDI) and 2-hydroxyethyl moth acrylate (HEMA). Molecular weight, acid number, and critical micelle concentration (CMC) of the synthesized reactive HPMCP and pristine HPMCP were measured and used as a polymeric surfactant in the emulsion polymerizations of styrene. In the preparation of HPMCP-hybrid poly styrene nanoparticles, 6, 9, 12, 18, and 24 wt% of HPMCPs were introduced, and the maximum rate of polymerization ($R_{p,max}$), the average number of radicals per particle (n), particle size distribution were investigated. In addition, core - shell morphology of the nanoparticles were observed by using TEM and their thermal stabilities were measured by using TGA. Reactive HPMCP showed higher $R_{p,max}$, smaller particle size, larger values of n and gel contents as compared with pristine HPMCP, due to the vinyl groups from HEMA, which can be reacted with styrene oligomers, in the reactive HPMCP.