Doo-Soo Yoon

Development and evaluation of targeting ligands surface modified paclitaxel nanocrystals.

To overcome the toxicity of excipient or blank nanoparticles for drug delivery nano-system, the surface modified paclitaxel nanocrystals (PTX-NC) have been developed. PTX-NCs were prepared by nano-precipitation method. The surface of PTX-NCs were modified by grafting with apo-transferrin (Tf) or hyaluronic acid (HA). The physical properties of PTX-NCs were evaluated by field emission scanning electron microscope (FE-SEM), zeta-sizer, zeta-potential, differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectrometry. In vitro drug release study was performed in phosphate buffered saline (PBS) with or without 0.5% (w/v) Tween 80 for 24h. Cellular uptake was studied at time intervals of 0.5, 1, and 2h in MCF-7 cells, and cell growth inhibition study was performed for 24h using MCF-7 cells (cancer cells), and HaCaT cells (normal cells). Three different types of PTX-NCs with a mean size of 236.0±100.6nm (PTX-NC), 302.0±152.0nm (Tf-PTX-NC) and 339±180.6nm (HA-PTX-NC) were successfully prepared. The drug release profiles showed 29.1%/6.9% (PTX (pure)), 40.7%/23.9% (PTX-NC), 50.5%/25.1% (Tf-PTX-NC) and 46.8/24.8% (HA-PTX-NC) in PBS with/without 0.5% (w/v) Tween 80 for 24h, respectively. As per the results, the drug release of PTX-NCs showed the faster release as compared to that of PTX (pure). Surface modified PTX-NCs exhibited higher values for cell permeability than unmodified PTX-NC in the cellular uptake study. Surface modified PTX-NCs inhibited the cell growth approximately to 60% in MCF-7 cells, however effect of surface modified PTX-NCs on normal cell line was lower than the PTX-NC and PTX (pure). In conclusion, biological macromolecules (Tf or HA) surface modified PTX-NC enhanced the cellular uptake and the cell growth inhibition.

Synthesis and Properties of Polybenzoxazole Precursors having Oligo(oxy ethylene) pendant

Abstract Poly(o-hydroxyamides)(PHAs) copolymers having oligo(oxy ethylene) pendant in the main chain were synthesized by solution polycondensation reaction at low temperature. Copolymer precursors were studied by fourier transform infrared(FT-IR), differential scanning calorimeter(DSC), thermogravimetric analyzer(TGA), universal testing machine(UTM) and limited oxygen index(LOI). The inherent viscosities of the PHAs measured at 35℃ in DMAc or DMAc/LiCl solution were in the range of 0.74∼1.42 dL/g. Solubility of the precursors with higher oligo(oxy ethylene) unit was increased, but the PBOs were nearly insoluble in a variety of solvents. The degradation temperature of the copolymer precursors was recorded in the ranges of 408∼664℃ in nitrogen and char yields showed 13∼59% values at 900℃. The mechanical properties and flame retardancy of copolymer precursors decreased with higher oligo(oxy ethylene) unit. Key Words : Polybenzoxazoles, Poly(o-hydroxyamide)s, Thermal cyclization reaction *

Study on the Isothermal Crystallization Behaviors of PEN/TLCP Blends

Abstract: The isothermal crystallization behaviors of blends of poly(ethylene naphthalate) (PEN) and a thermotropic liquidcrystalline polymer (TLCP) were investigated by differential scanning calorimetry (DSC) as functions of crystallization tem-perature and blend composition. Avrami analyses were applied to obtain information on the crystal growth geometry andthe factors controlling the rate of crystallization. The crystallization kinetics of the PEN/TLCP blends followed the Avramiequation up to a high degree of crystallization, regardless of crystallization temperature. The calculated Avrami exponentsfor PEN/TLCP revealed three-dimensional growth of the crystalline region in each blend. The crystallization rate of eachblend increased as the crystallization temperature decreased, and decreased as the TLCP content increased. The crystalli-zation of PEN in the blend was affected by the addition of TLCP, which acts as a nucleating agent.Keywords: Avrami equation, isothermal crystallization kinetics, nucleating agent, PEN/TLCP blend

Synthesis and Thermal Properties of Aromatic Poly(o-hydroxyamide)s Containing Phenylene Diimide Unit

Abstract In this study we attempt to modify the backbone structure and improve processibility of PBO having high melting and glass transition temperature. A series of aromatic poly(o-hydroxyamide)s(PHAs) were synthesized by direct polycondensaton of diacides containing diimide unit with two types of bis(o-aminophenol)s including 3,3′-dihydroxybenzidine and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. PHAs were studied by FT-IR, 1 H-NMR, DSC and TGA. PHAs exhibited inherent viscosities in the range of 0.34~0.65 dL/g at 35 ℃ in DMAc solution. The PHA 1 and 6F-PHA 6, introducing o-phenylene unit in the main chain showed excellent solubilities in aprotic solvents such as NMP etc. However, the PHA 3, having p-phenylene unit was not even dissolved perfectly with LiCl salt. 6F-PHAs were readily soluble at room temperature in aprotic solvents except 6F-PHA 3. But they showed better solubility than that of PHAs. The polybenzoxazoles(PBOs) were quite insoluble in other solvents except partially soluble in sulfuric acid. PBOs exhibited relatively high glass transition temperatures(Tg) in the range of 306~311℃ by DSC. The maximum weight loss temperature and char yields of PHA3 and 6F-PHA3 showed the highest values of 658 ℃ and 653 ℃, 62.6 % and 62.1 %, respectively.

Synthesis and Properties of Semi-flexible Liquid Crystalline Polyesters with Rigid Lateral Group

Jong-Ryul Park, Eung-Jae Lee, Doo-Soo Yoon, Moon-Soo Bang and Jae-Kon Choi Division of Advanced Materials Science and Engineering, Kongju National University, Cheonan 330-717, Korea Dept. of Bioenvironmental & Chemical Engineering, Chosun College University of Science & Technology, Gwangju 501-744, Korea Dept. of Biochemical & Polymer Engineering, Chosun University, Gwangju 501-759, Korea (Received November 6, 2013, Revised November 13, 2013, Accepted November 18, 2013)