• Elastomers and Composites
• /
• v.51 no.2
• /
• pp.138-146
• /
• 2016

It is an inconvenience for silica nano-particles to dry again when using it in that they cohere each other through moisture in the air. Acrylamide groups were introduced to improve such inconvenience and copolymerized with silica nano-particles and then we copolymerized again with polyamic acid in order to increase thermal characteristic. Amide block copolymers were prepared using silica and (3-mercaptopropyl) trimethoxysilane (MPTMS) with a siloxane group, using 2,6-Lutidine as a catalyst. Amide block polymers and copolymers were synthesized via ATRP after brominating pyromellitic dianhydride (PMDA) and polyamic acid of methylene diphenyl diamine (MDA), using ${\alpha}$-bromo isobutyryl bromide. Characteristic peaks of copolymer with amide and imide groups and patterns of amorphous polymers were researched by FT-IR and XRD analyses and the analysis of surface characteristic groups was conducted via XPS. A change in thermal properties was examined through DSC and TGA and solubility for solvents was also researched.

• Journal of the Korean Society of Safety
• /
• v.7 no.2
• /
• pp.57-62
• /
• 1992

In this thesis, the electrification phenomenon was studied by measurement of charging current and discharging current in polymers when the carriers generated by corona discharge were supplied to the surface of polymers. Corona charging current of PVC, polar and noncrystalline polymer, was larger than that of nonpolar and amorphous polymers. Corona charging current on the specimen of naked upper surface (CIM) was larger than charging current on the specimen of electrode made. Carrier injection differed from interfacial phase of polymer surFace. The transfer phenomenon vaned with chemical structure of polymer and then the polar effect of PVC was remarkable because of large electron affinity of Cl. In the characteristics of discharging current of PVC, the abnormal current was observed. It was supposed that this phenomena presented the trap of injected carriers in PVC and that static electricity phenomenon was generated by trap.

• Bulletin of the Korean Chemical Society
• /
• v.18 no.12
• /
• pp.1249-1256
• /
• 1997

Single phase La1-xSrxCoO3 (x≤0.2) was synthesized as a uniform sized 100 nm particulates with relatively high surface area of 20-30 m2/g, at low temperature (≥600 ℃), from a polymeric gel precursors prepared by using poly(vinyl alcohol) as homogenizer. No minor phase developed during the crystallization when polymer/metal mole ratio was higher than 3. As the polymer/metal mole ratio was raised in the gel, the amount of carbonaceous residues in the amorphous solid precursor prepared by heating the gel at 300 ℃ increased. Most of the residues were eliminated by exothermic thermal decomposition around 400 ℃. The amount of residual carbon (less than 1%) left in the crystalline La1-xSrxCoO3 decreased as more polymer was used, eliminating detrimental effect which might be posed by using large amount of organic homogenizer. The crystal structure of La1-xSrxCoO3 synthesized at temperature lower than 800 ℃ was observed to be shifted from rhombohedral to more symmetric cubic. The structure shifted back to rhombohedral as the cubic sample was annealed at 1000 ℃.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.9
• /
• pp.2949-2954
• /
• 2012

Nano ZnO with an average size of 8 nm was prepared by thermal decomposition of zinc oxalate at $450^{\circ}C$. A series of based composite polymer electrolyte PEO-$LiClO_4$ and nano ZnO as a filler have been synthesized using solution cast technique, with varying the filler ratio systematically. XRD, DSC and FTIR studies have been conducted to investigate the structure and interaction of different groups in the composite polymer electrolyte. Effect of nano ZnO ceramic filler concentration on the structure of composites and their electrical properties (DC-conductivity, AC-conductivity, dielectric constant, dielectric loss and impedance) at different frequencies and temperatures was studied. Melting temperature ($T_m$) of PEO decreased with the addition of both $LiClO_4$ salt and nano ZnO filler due to increasing the amorphous state of polymer. All composite samples showed an ionic conductivity. The maximum room temperature ionic conductivity is found for $(ZnO)_{0.5}(PEO)_{12}(LiClO_4)$ composite sample. All the results are correlated and discussed.

• Transactions of the Korean hydrogen and new energy society
• /
• v.33 no.2
• /
• pp.176-182
• /
• 2022

Since the various characteristics of the polymer electrolyte membrane are not clearly identified, it is difficult to predict and design applications for various conditions. In this study, as a previous study on the aging of the polymer electrolyte membrane, a study was conducted on the change of mechanical properties according to the aging of the polymer electrolyte membrane. Through the tensile test of Nafion 117, the mechanical properties change due to aging was confirmed. As a result of the tensile test, it was confirmed that the aged Nafion 117 had reduced tensile strength. Through DSC measurement, aged Nafion confirmed that the glass transition temperature and enthalpy change were low, which is thought to be the effect of molecular motion and transition due to the lapse of time. The effect is thought to cause a difference in the amount of change in enthalpy, resulting in a difference in mechanical properties during tension.

• Polymer(Korea)
• /
• v.24 no.1
• /
• pp.133-139
• /
• 2000

Poly(ethylene glycol) with number-average molecular weight (M$_{n}$) of 200 (PEG 200) or 400 (PEG 400) was reacted with various linking agents (CH$_2$Cl$_2$, CH$_2$Br$_2$, CH$_2$I$_2$, Br(CH$_2$)$_3$Br) in the presence of alkali to form of oxyalkylene linked chains. Molecular weights of copolymers were controlled using feed mole ratio of alkali/CH$_2$C1$_2$/PEG. The M$_{n}$ of the polymers measured by end group analysis and that measured by GPC agreed well. Molecuglar weights of polyether copolymers obtained from PEG 200 and PEG 400 were about 500~8500 and 1000~2000, respectively. Polyether copolymers prepared from PEG 400 showed melting points of around 1$0^{\circ}C$. Glass transition temperatures of the copolymers were around -75$^{\circ}C$ and the crystallinity was about 0~25%. The polyether copolymers prepared from PEG 200 had no crystallinity below the M$_{n}$ of 2500. 2500.

• Journal of Pharmaceutical Investigation
• /
• v.38 no.2
• /
• pp.119-126
• /
• 2008

Solid dispersions of poorly water-soluble drug, sibutramine, were prepared with hydrophilic polymer, poly-N-vinylpyrrolidone (PVP), hydroxypropylmethylcellulose (HPMC) and organic acid, citric acid, to improve the solubility of drug. Physicochemical variation and shape of microsphere were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and Fourier-transform infrared spectroscopy (FT-IR). Microspheres containing additives showed more spherical shape than non additive microspheres. In vitro release behavior of microspheres presented at simulated gastric fluid (pH 1.2) and simulated intestinal fluid (pH 6.8). The solid dispersion form transformed the drug into an amorphous state and dramatically improved its dissolution rate. These data suggest that the solid dispersion technique is an effective approach for developing the appetite depressant drug products and various pharmaceutical excipients are able to control the release behaviors.

• Macromolecular Research
• /
• v.9 no.4
• /
• pp.228-237
• /
• 2001

The evolution of conformational constraints in bisphenol-A polycarbonate (BAPC) upon quiescent bulk crystallization was quantitatively analyzed from calorimetric study employing a rigid amorphous fraction (RAF) as an indicator of the level of conformational constraints. From the correlation between corrected crystallinity (X$\sub$c/) and total rigid fraction (f$\sub$r/), it was found that, regardless of molar mass distribution and thermal treatment conditions, semicrystalline BAPC always exhibits greater f$\sub$r/ than X$\sub$c/ maintaining a quantitative relationship of f$\sub$r/〓2X$\sub$c/ in the range of 0.0 $\sub$c/< 0.4. This directly indicates the evolution of approximately the same amount of RAF as X$\sub$c/, (i.e., RAF〓X$\sub$c/) upon bulk crystallization of BAPC. It was also found that T$\sub$g/ per se and T$\sub$g/ broadening enhance as RAF increases, and there appears to be a critical level of RAF (>0.2) needed to initiate significant changes in both quantities.

• Macromolecular Research
• /
• v.14 no.6
• /
• pp.603-609
• /
• 2006

Tricyanopyrrolidene chromophores were prepared in order to compare their macroscopic nonlinear optical (NLO) properties with a conjugated structure through the long molecular axis. A thiophene or phenyl ring was tethered to an ethylenic bond; it may act as a lateral moiety to disrupt the planarity of a chromophore and lessen the electrostatic interaction. Thin film composites of these chromophores dissolved in amorphous polycarbonate (APC) were fabricated. Real time pole and probe method was employed to investigate the change of electro-optic (EO) signal during poling. The EO properties and their relaxation behaviors of the guest-host systems containing newly synthesized chromophores were investigated in detail.

• Proceedings of the KIEE Conference
• /
• 1993.07b
• /
• pp.1262-1264
• /
• 1993

An amorphous $Se_{75}Ge_{25}$ thin film as inorganic resist for the focused ion beam lithography(FIBL) is investigated. This film offers an attractive potential alternative to polymer resists because of a number of advantages, such as the possibility of preparing physically uniform films of thickness as small as 200A and obtaining both positive and negative resist action in the same material, compatibility with dry processing, the sensitivity on optical, e-beam and ion beam exposure, the high-temperature stability, etc. In previous paper, the defocused ion beam-induced characteristics in a-$Se_{75}Ge_{25}$ film has been propose. Practically it is neccesary to know the relation with resist and source ions. For the purpose, the ion stopping power, the ion projected range and ion transmission coefficiency are studied. In this paper, the theoretically calculated values of parameters are presented and compared with theory.