Jae-Kon Choi

Synthesis and anti-cancer efficacy of rapid hydrolysed water-soluble paclitaxel pro-drugs

A new series of poly(ethylene glycol)(PEG)–paclitaxel conjugates that increases water solubility of paclitaxel was synthesized. We developed well-designed self-immolating linkers between a drug and a water-soluble polymer moiety which gave an extremely rapid hydrolysis rate to convert a pro-drug into a parent drug without any reduction in drug efficacy. The self-immolating spacer groups were introduced between the solubilizing PEG and C7-OH of paclitaxel in order to control the rate of enzymatic hydrolysis. All these pro-drugs had a water-solubility of 400 mg/ml or more compared with a solubility of about 0.01 mg/ml. The rate of hydrolysis for the pro-drugs in rat plasma showed considerable variation of t ½ ranging from 0.94 min to 42.7 min. Toevaluate the anti-tumor efficacy of the pro-drug which had the fastest enzymatic hydrolysis rate, the growth inhibitory effect (IC50), the anti-tumor activity and the anti-metastatic potential of the pro-drug were examined. The pro-drug was potent to inhibit the growth of various cancer cell lines, such as human lung, ovarian, colon and melanoma cancer cells. On the development of melanoma lung colonies in C57B/6 mice following intravenous administration of metastatic murine B16/F10 melanoma cells, the pro-drug seems to be more efficacious than paclitaxel. The reduction of the number of melanoma lung colonies was 46.9% (dose: 5mg/kg) with pure paclitaxel, and 24.5%, and 40.0% with the pro-drug in the dose of 0.71 mg paclitaxel equivalent/kg and 1.42 mg paclitaxel equivalent/kg, respectively.

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 *

Preparation and Flame Retardancy of Poly(benzoxazole imide) Having Trifluoromethyl Group in the Main Chain

ABSTRACT ：A series of poly(hydroxyamide)s (PHAs) having trifluoromethyl group were prepared by direct polycondensatio nof aromatic diimide-dicarboxylic acids with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane by thionyl chloride and triethyl amine in N -methyl-2-pyrrolidinone (NMP). The PHAs exhibited inherent viscosity in the range of 0.54-0.96 dL/gat 35℃ in DMAc solution. All PHAs were readily soluble in a variety of organic solvents, whereas the polybenzoxazoles (PBOs) were quite insoluble except partially soluble in sulfuric acid. PHAs were converted to PBOs by thermal cyclingreaction with heat of endotherm. The maximum weight loss temperature of the PHAs occurred in the range of 559-567℃. The PBOs showed relatively high char yields in the range of 47-59%. Pyrolysis Combustion Flow Calorimeter (PCFC)results of the PBOs showed 12-19 W/g heat release rate (HRR), and 2.7-3.6 kJ/g total heat release (total HR). The HRRof PBO 1 showed the lowest value of 12 W/g, which was 37% lower than that of PBO 3 (19 W/g).

Randomly Sulfonated Liquid Crystalline Polymers Containing Triad Mesogen of Butylene Terephthalate

A thermotropic liquid crystalline polymer (LCP) containing a terephthaloyl bis(4-oxybenzoyl) (Triad) rigid moiety and a butylene terephthalate flexible unit was solution-polymerized and was subsequently partly sulfonated. It was found that the introduction of sulfonic acid groups to the LCP did not change the position of the DSC peak for the nematic-to-isotropic transition of the LCP (T n-i). However, the sulfonation induced a peak related to the melting of crystalline phase of the Triad domains (T m(T)). When the acid groups of the sulfonated LCP were neutralized with NaOH, the T n-i DSC peak shifted to lower temperatures with a strong decrease in its size, but the T m(T) DSC peak did not change its position strongly. Furthermore, a new peak for the melting of crystalline phase of the butylenes domains (T m(BT)) appeared at much lower temperatures. The above results suggested that the sulfonation introduced ionic characters to the TLCP polymer successfully; as expected, it changed the liquid crystalline characters of the TLCP significantly.

Synthesis and Properties of Thermotropic Poly(Ester-Amide)S Having Semiregular Monomer Sequences

Abstract Dichloride of 4,4′-(carbonylimino)dibenzoic acid was polymerized in 1,1,2,2-tetrachloroethane with a series of monosubstituted hydroquinone (series I) or α, ω-bis(4-hydroxyphenoxy)alkanes (series II) having alkane units of varying length. the polymers obtained were characterized by IR and NMR spectroscopy, solution viscosity measurements, and differential scanning calorimetry (DSC). Formation of mesophase and thermal behavior also were studied on a hot-stage attached to a polarizing microscope. All of the polymers were thermotropic and the transition temperatures were highly dependent on the nature of substituents on hydroquinone in the first series and on the length of alkylene spacers in the second series.

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

Preparation and Characteristics of the Blends of Polyimide and Polybenzoxazole Having Imide Ring

Polymer blends were prepared by solution blending poly(amic acid) (PAA) and poly(o-hydroxy amide) (PHA) having imide groups in the main chain. The polymers and their blends were characterized by using FTIR, FT NMR, DSC, TGA, SEM, XRD, UTM, and LOI. The solubility study revealed that the blends were readily soluble in aprotic solvents such as DMF, DMAc, DMSO, and NMP. The maximum weight loss of the blends occurred in the range of , and the maximum weight loss temperature increased with increasing the PHA content. The PBO/PI blends showed relatively high char yields (i.e. 56-69 wt%). The LOI values of the blends were in the range of 24.5-28.1% and increased with increasing the PHA content. The initial modulus and tensile strength of the blends increased by 57 to 121% and by 67 to 107%, respectively, compared to the values of PAA. Especially the initial modulus and tensile strength of the PHA/PAA=2/8(wt/wt) showed the highest values of 4.87 GPa and 108 MPa, respectively. The PHA domains of in their size were more or less uniformly dispersed. The interfacial adhesion between PAA and PHA was found to be good.

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)