• Journal of Pharmaceutical Investigation
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• v.20 no.3
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• pp.51-76
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• 1990

It is sometimes said lately that the pH of the human gastric juice is significantly different among individuals. Thus, the dissolution behavior of coated solid dosage forms should preferably be independent of the pH of the test solution. With these points as a background, the effect of pH on the dissolution velocity of coated tablets was studied to compare that of Pharmacoat with other gastric soluble film coating materials. Three viscosity types of Pharmacoat have been available(3, 6 and 15cP) until now. the 6cP type has been considered to be the most suitable for a tablet coating amongst the three types. The 3 cP type with a low degree of polymerization, is capable of providing high concentration, but the film strength is so inferior that sometimes cracking of the film may occur. On the other hand, in the case of the 15cP type, high polymer concentration cannot be achieved because of the high dgree of polymerization, and thus it is uneconomical for coating. Now, there is a strong demand to reduce the coating time even when HPMC is used in the 6cP type in order to reduce the coating cost. In order to improve this problem, we have concentrated our attention on reducing the viscosity value of HPMC to an allowable lower limit from 6cP. As a result of this study, it was found that the reduction of the viscosity value to around 4.5cP enabled the use of a higher solution concentration and an incidental shorter coating time without giving any substantial adverse effects on the properties of coated preparations. These experiment results are presented in the later part of this presentation. Based on this study, we have added the viscosity type of 4.5cP as one of the Pharmacoat products as Pharmacoat-645.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.1-5
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• 1998

The dispersing behaviors of oligomer-type anionic surfactants, cooligomers of diethyl maleate(CmD-Na) or maleic anhydride (CmM-Na) and $C_4{\sim}C_{16}$ alkyl vinylether, which have a different alkyl chain length of the hydrophobic group or degree of polymerization, were studied on the aqueous suspension of ${\alpha}-$ and ${\beta}-$ copper phthalocyanine and carbon black particles. In case of the side alkyl chain length of $C_4{\sim}C_{10}$ of CmD-Na, the dispersing actions were good in the concentration range of 0.01 to 0.1%. Especially, side alkyl groups played an important role in the orientation adsorption on the surface of pigment particles, and oligomers having smaller degrees of polymerization were more effective in the dispersing action, but did not affect the dispersability of carbon black.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.403-408
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• 2006

To enhance the dental properties of polymeric dental restorative composite activated by visible-light, the surface of hydrophilic silica nanoparticle was hydrophobically treated using $\gamma$-methacryloxypropyltrimethoxysilane ($\gamma$-MPS) coupling agent. Structural properties and dispersity of silica in the composite was compared with the hydrophobicity of silica. Polymerization characteristic of the composite was also evaluated. Degree of hydrophobicity of silica nanoparticle was considerably improved with an increase of $\gamma$-MPS upto 40 wt% and converged asymptotically. Additionally, with an increase of the hydrophobicity of silica nanoparticle, the dispersity of silica was improved and the residual monomer in the composite was not detected from nuclear magnetic resonance experiment which indicated superior polymerization behavior.

• Polymer(Korea)
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• v.25 no.2
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• pp.168-176
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• 2001

The effect of novel N-crotyl-N,N-dimethyl-4-methylanilinium hexafluoroantimonate (CMH) curing agent as a thermal latent initiator on thermal behaviors, rheological properties, and thermal stability of diglycidylether of bisphenol A (DGEBA) epoxy cationic system was investigated. From DSC measurements of DGEBA/CMH system, it was shown that this system exhibits an excellent thermal latent characteristic at a given temperature. The conversion and conversion rate of DGEBA/CMH system increased with increasing the concentration of initiator, due to high activity of CMH. Rheological properties of the system were investigated under isothermal condition using a rheometer The gelation time was obtained from the analysis of storage modulus (G'), loss modulus (G"), and damping factor (tan $\delta$). As a result, the reduction of gelation time was affected by high curing temperature and concentration of CMH, resulting in high degree of network formation in cationic polymerization, due to difference of activity. The thermal stability of the cured epoxy resin was discussed in terms of the activation energy for decomposition and thermal factors determined from TGA measurements.ents.

• Korean Journal of Materials Research
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• v.23 no.5
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• pp.276-280
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• 2013

Coal tar is the primary feedstock of premium graphitizable carbon precursor. Coal tars are residues formed as byproducts of thermal treatments of coal. Coal tar pitches were prepared through two different heat treatment schedules and their properties were characterized. One was prepared with argon and oxidation treatment with oxygen; the other was prepared with oxygen treatment at low temperature and then argon treatment at high temperature; both used coal tar to prepare coal tar pitches. To modulate the properties, different heat treatment temperatures ($300{\sim}400^{\circ}C$) were used for the coal tar pitches. The prepared coal tar pitches were investigated to determine several properties, such as softening point, C/H ratio, coke yield, and aromaticity index. The coal tar pitches were subject to considerable changes in chemical composition that arose due to polymerization after heat treatment. Coal tar pitch showed considerable increases in softening point, C/H ratio, coke yields, and aromaticity index compared to those characteristics for coal tar. The contents of gamma resin, which consists of low molecular weight compounds in the pitches and is insoluble in toluene, showed that the degree of polymerization in the pitches was proportional to C/H ratio. Using an oxidizing atmosphere like air to prepare the pitches from coal tar was an effective way to increase the aromaticity index at relatively low temperature.

• Restorative Dentistry and Endodontics
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• v.27 no.1
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• pp.87-94
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• 2002

The purpose of this study was to evaluate the color changes of composite resin polymerized with three type of light curing units. Composite resin (Z100, shade A2) were applied in a cylindrical metal mold(2 mm thick, 7 mm diameter). Twenty specimens according to light curing units were made. Group 1 : the specimens were polymerized with Apollo 95E for 3seconds(1370 mW/$\textrm{cm}^2$). Group 2 : the specimens were polymerized with XL 3000 for 40seconds (480 mW/$\textrm{cm}^2$). Group 3 : the specimens were polymerized with Spectrum 800 for 10 seconds(250 mW/$\textrm{cm}^2$) and 30 seconds(700 mW/$\textrm{cm}^2$). The microhardness values(VHN) of upper and lower surfaces specimens after light polymerization were measured for the degree of polymerization. All specimens were stored in distilled water at 6$0^{\circ}C$ for 30 days. The color characteristics(L$^*$, a$^*$, b$^*$) of the specimens before and after immersion were measured by spectrophotometer and the total color difference ($\Delta$E$^*$) was computed. The results obtained were as follows : 1. The microhardness values of Group I showed significantly lower than those of Group II and III (p<0.05). 2. In all groups the $\Delta$E$^*$ values presented below 2.0. 3 Group I showed the highest $\Delta$E$^*$ values followed order from highest to lowest by Group II and III (p<0.05).

• Polymer(Korea)
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• v.38 no.5
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• pp.671-675
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• 2014

Well-defined star shaped and linear block copolymers were synthesized to study the dispersion stability of copper phthalocyanine (CuPc). We synthesized dispersants using (2-dimethylamino) ethyl methacrylate (DMAEMA) and poly(ethylene glycol) methyl ether methacrylate) (PEGMA) by activators generated by electron transfer (AGET) atom transfer radical polymerization (ATRP). pDMAEMA-b-pPEGMA copolymers were characterized by GPC and NMR. Furthermore, we studied the effect of the dispersion stability of copper phthalocyanine by controlling the degree of polymerization of PEGMA as a stabilizing group. The 4-arm star shaped polymeric dispersant showed better dispersion stability of CuPc at $25^{\circ}C$ for 7 days.

• Elastomers and Composites
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• v.46 no.4
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• pp.304-310
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• 2011

In this study, we prepared poly(ethylene-ter-1-hexene-ter-divinylbenzene) using briged rac-$Et[Ind]_2ZrCl_2$ or unbriged $Cp_2ZrCl_2$ metallocene catalysts. Bridged rac-$Et[Ind]_2ZrCl_2$ catalyst showed relatively good results compared with unbridged one. When cocatalyst/catalyst molar ratio was 3000, catalytic activity indicated more than 8000(kg of polymer/$mol{\cdot}h$) which was very remarkable value. As a polymerization time increased, the weight-average molecular weight of the terpolymer gradually increased to some degree. In the case of a polymerization time of 50 minutes, the state of the terpolymer became amorphous. The range of the weight-average molecular weight and the densities of the terpolymer was 110,000~200,000 and $0.85{\sim}0.89g/cm^3$, respectively. The thermal properties and the structure of the terpolymer were also identified.

• Polymer(Korea)
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• v.37 no.5
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• pp.563-570
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• 2013

Poly(vinyl pivalate) (PVPi) was bulk polymerized to make poly(vinyl alcohol) (PVA) microfibrils to apply for polymeric embolization coils replacing metalic coils. Then, syndiotactic PVA (s-PVA) microfibrils having number-average degree of polymerization of 1100 and s-diad content of 60.4% were prepared via saponification of the PVPi with no separate spinning process. To make s-PVA microfibrils with radiopacity, zirconium dioxide ($ZrO_2$) and barium sulfate ($BaSO_4$) were added into s-PVA microfibrils during saponification. The computed tomography (CT) value indicating radiopacity reached up to over 1000 when the amount of $ZrO_2$ and $BaSO_4$ were 12 and 6 wt%, respectively.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.2
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• pp.273-279
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• 2004

Recently, newly developed single high-intensity LED curing lights for composite resins are claimed to have a higher intensity than previous LED curing lights and to results in optimal properties and short curing time. The purpose of this study was to determine the curing effectiveness of the curing units and to evaluate the relationship between the degree of polymerization and distance from curing light tip end to resin surface. One composite resin was tested(Filtek Z250). Thin film specimens were cured with a LED curing unit(Elipar Freelight 2, 10s), Plasma Arc curing unit(Flipo, 6s), Halogen curing light(XL3000, 20s) at four curing light tip to the resin surface(0mm, 2mm, 4mm, 6mm). Degree of conversion of composite resins were determined by a Fourier Transform Infrared Spectrometer(FTIR). From the present study, the following results were obtained. 1. In all curing units, relative light intensity was significantly decreased according to the increase of distance of light tip to the resin surface(p<0.05). LED curing units showed a higher percentile decrease in intensity than other curing units. 2. In all curing units, degree of conversion was decreased as increase of the distance but no statistically significant difference(p>0.05) except between 4mm and 6mm(p<0.05). 3. When comparing degree of conversion of light curing units at each distance(0mm, 2mm, 4mm, 6mm), LED curing light had a higher degree of conversion than plasma arc and halogen curing lights at 0, 2, 4mm(p<0.05). At 6mm, there was a no significant difference among the curing units(p>0.05).