• Macromolecular Research
• /
• v.16 no.5
• /
• pp.418-423
• /
• 2008

Poly[(R)-3-hydroxy butyrate] (PHB) and methoxy poly(ethylene glycol) (mPEG) were conjugated by the transesterification reaction with tin(II)-ethylhexanoate (Sn(Oct)-II) as a catalyst. Hydrophobic PHB and hydrophilic mPEG formed an amphiphilic block copolymer which was formed with the self-assembled polymeric micelle in aqueous solution. In this study, we tried to determine the optimum ratio of hydrophobic/hydrophilic segments for controlled drug delivery. The particle size and shape of the polymeric micelle were measured by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Their size were 61-102 nm with various block ratios. Griseofulvin was loaded in the polymeric micelle as a hydrophobic model drug. The loading efficiency and release profile were measured by high performance liquid chromatography (HPLC). The model drug in our system was constantly released for 48 h.

• Corrosion Science and Technology
• /
• v.8 no.6
• /
• pp.223-226
• /
• 2009

Polymer coatings are commonly applied to metal substrates to prevent corrosion in aggressive environments such as high humidity and under salt water. Once the polymer coating has been breached, for example due to cracking or scratches, it loses its effectiveness, and corrosion can rapidly propagate across the substrate. The self-healing system we will describe prevents corrosion by healing the damage through a healing reaction triggered by the actual damage event. This self-healing coating solution can be easily applied to most substrate materials, and our dual-capsule healing system provides a general approach to be compatible with most common polymer matrices. Specifically, we expect an excellent anti-corrosion property of the self-healing coatings in damaged parts coated on galvanized metal substrates.

• Proceedings of the Korean Fiber Society Conference
• /
• 1996.10a
• /
• pp.468-472
• /
• 1996

A series of UV-curable polyurethane acrylate ionomer were synthesized from isophorone diisocyanate(IPDI), poly(tetramethylene ether glycol)(PTMG), 2,2-bis(hydroxymethyl)propionic acid (CMPA), triethylamine(TEA), 2-hydroxy ethyl acrylate (HEA), and dibutyl tin dilaurate (DBT) as a catalyst. 2,2-dimethoxy-2-phenyl acetophenone(DMPAP) was used as a photoinitiator. The films of UV-cured polyurethane acylate ionomer were prepared by casting the formulated materials onto a glass plate at room temperature and cured using a medium pressure mercury lamp (80 W/cm, max = 365nm). Effects of DMPA content, molecular weight of PTMG and degree of neutralization on the properties were invesigated. It is found that the storage modulus increased with increasing DMPA content. The glass transition temperature of sample A shifted to higher temperature as the content of DMPA was increased. Tensile modulus also increased with increasing DMPA content. Modulus and Tg decreased with increasing molecular weight of PTMG form 650 to 2000. With increasing the degree of nutralizaion, ionomers exhibited improved modulu.

• Polymer(Korea)
• /
• v.35 no.1
• /
• pp.52-59
• /
• 2011

L-PLA or D-PLA was synthesized in bulk at $140^{\circ}C$ by ring opening polymerization(ROP) of L-lactide or D-lactide as a monomer using tin(II) octoate and lauryl alcohol as a catalyst and an initiator with changing the amounts of catalyst(0.25~1.0 wt%) and initiator(0.l~0.5 wt%). And stereocomplex-PLA was prepared by L-PLA/D-PLA having a wide range of molecular weight(30000~90000 g/mol) and L-PLA/D-PLA blends having different mixing ratio ($X_D$). The melting temperature. thermal degradation temperature and thermal stability of stereocomplex-PLA were higher than those of homopolymers(L-PLA, D-PLA). We supposed that these improvements arose from a strong interaction between L-PLA and D-PLA. The improved mechanical properties and changes in morphology of LPLA/D-PLA blends were compared to those of homopolymers(L-PLA, D-PLA).

• Polymer(Korea)
• /
• v.34 no.1
• /
• pp.8-13
• /
• 2010

The physical properties of polymeric foams depend on the density of foams, physical properties of base polymers, the content of open cells, and cell structures including the size and its distribution, the shape of cell, and the thickness of skin layer. The foam density is affected by the chemistry of raw materials, the concentration of crosslinking agent and the blowing agent as well as the operating parameters during production process. In this study, the basic formulations of foams are composed of polyester polyol, MDI, amine catalyst, tin catalyst, silicone surfactant, and water. Cross-linking density of polyurethane was increased by using chain extenders. Also, the mechanical properties of polyurethane foam were improved by using the inorganic fillers (silica 1,2 and talc 1,2) having different $SiO_2$ contents and particle sizes. We investigated the properties of modulus, tensile strength, compressive strength and hardness of foams obtained by changing kind of inorganic filler and chain extender, and observed the distribution of inorganic filler as well as variation of cell size within the foams by electron microscopy.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1338_1339
• /
• 2009

Dye-sensitized solar cell (DSC) consists of photo electrode, counter electrode and electrolyte. Photo electrode has titanium oxide layer with dye molecule to create electrons. And counter electrode is made of one layer that has catalytic ability for redox system such as the iodide/triiodide couple. Most DSC researchers use platinum as catalyst on counter electrode because platinum has good catalytic ability and conductivity. Platinum is doped on fluorine-doped tin oxide glass with different methods such as sputtering method, electrochemical method and so on. In this paper, we deposit platinum on counter electrode glass with two methods. One is the radio frequency (RF) sputtering method and the other is the chemical method with heating treatment. Finally, we compare the photovoltaic characteristics of DSCs that are assembled using two different counter electrodes.

• The Korean Journal of Ceramics
• /
• v.5 no.2
• /
• pp.125-130
• /
• 1999

After $SnO_2$ fine powder by precipitation method, Ca as crystallization inhibitor and Pd as catalyst were added to $SnO_2$ raw material by various methods. Thick film device was fabricated on the alumina substrate by mixing ethylene glycol and such mixed powders. The sensing characteristics of the device for methane gas were investigated. The most excellent gas sensing property was shown by the thick film device fabricated by Method 3 in which Ca and Pd doped $SnO_2$ powder is prepared by mixing $SnO_2$ powder, 0.1 wt% Ca acetate and 1 wt% $PdCl_2$ in deionized water and by calcining the mixture, after $Sn(OH)_4$ is dried at $110^{\circ}C$ for 36h. The sensitivity of the sensor fabricated with $SnO_2$-0.1 wt%Ca acetate-1wt%$PdCl_2$ powder heat-treated at $700^{\circ}C$ for 1h was about 86% for 5,000 ppm methane in air at $350^{\circ}C$ of the operating temperature. Response time and recovery were also excellent.

• Korean Journal of Food Science and Technology
• /
• v.12 no.3
• /
• pp.193-199
• /
• 1980

A series of tests were conducted on the reesterification of rice bran oil containing high free fatty acids (acid value=119.7) with theoretical equivalent of glycerol. Test results showed that reaction rate (in terms of decrease in acid value) was increased as the reaction temperature was increased regardless of the presence of the catalyst and reaction time (42.7, 21.5 and 10.0 at $170^{\circ}C,\;210^{\circ}C\;and\;250^{\circ}C$, respectively) and as the reaction time was increased regardless of the temperature and the presence of the catalyst (31.1 vs 18.3 for 3 hrs vs 6 hrs). The presence of the catalyst (0.2% tin chloride) also accelerated the rate regardless of the reaction temperature and time (36.9 vs 12.5). Analysis by column chromatography showed that content of triglyceride in the oil was increased to 72.9% and 61.1% from 10.4% and content of free fatty acids in the oil was decreased to 1.4% and 6.1% from 60.2%, when the degummed oil was esterified at $250^{\circ}C$ for 6 hrs in the presence of and in the absence of the catalyst, respectively. The results estimated from the iodine values indicate that polymer formation was not significant, when the oil was esterified for 6 hrs at temperatures up to $210^{\circ}C$. However, it was somewhat significant for the oil esterified at $250^{\circ}C$ for 6 hrs. The catalyst did not affect the polymer formation. Analysis by high performance liquid chromatography showed that oleic acid (42.5%), linoleic acid (29.0%) and palmitic acid (20.3%) were the major fatty acid components of the rice bran oil.

• Journal of the Korean Electrochemical Society
• /
• v.11 no.3
• /
• pp.141-146
• /
• 2008

Electrocatalytic activities and stabilities of Pt supported on Sb-doped $SnO_2$ (ATO) were examined for ethanol oxidation reactions. Pt colloidal particles were deposited on ATO nanoparticles (Pt/ATO) and the prepared electrocatalysts were characterized by X-ray diffraction, transmission electron microscopy (TEM), and cyclic voltammetry. Electrochemical activity of the Pt/ATO for ethanol electro-oxidation was compared to those of Pt supported on carbon (Pt/C) and commercial PtRu/C. The activitiy of the Pt/ATO was much higher than those of the Pt/C and commercial PtRu/C. The Pt/ATO exhibited much higher electrochemical stabilities than the Pt/C in 0.5M ${H_2}{SO_4}$ and in 0.5M ${H_2}{SO_4}$/1M ${C_2}{H_5}OH$. According to TEM, the growth rate of Pt particles was lower in the Pt/ATO than it was in the Pt/C. The ATO nanoparticle appears to be a promising support material that promotes electrochemical reactions and stabilizes catalyst particles in direct ethanol fuel cell.

• Applied Chemistry for Engineering
• /
• v.10 no.7
• /
• pp.1028-1034
• /
• 1999

Poly(lactic acid) is expected to be one of the most promising biodegradable polymers. However, the high molecular weight polymer could be obtained by ring-opening polymerization process conventionally, which raises the production cost and decreases the final yield. In this study, linear and star-shaped poly(L-lactic acid)s were prepared by direct solution polycondensation method and their physical and thermal properties were examined. Tin compounds were found to be effective catalyst for the preparation of high molecular weight polymers. When 0.2g (0.5 wt % of monomer) of $SnCl_2$ and 100 mL of p-xylene were used, the polymer yield and molecular weight were relatively high. As a means to obtain higher molecular weight polymer easily in the direct polycondensation system, dipentaerythritol(dipet) or pentaerythritol(pet) was introduced as a multifunctional branching monomer to provide a star-shaped poly(lactic acid). Moderately high molecular weight polymers with the inherent viscosity values up to 1.14 dL/g(weight-average molecular weight of about 140000 by GPC) were obtained and could be cast strong and transparent films.