Keon Hyeong Kim

Drug Release Behavior of Poly(ε-caprolactone)-b-Poly(acrylic acid) Shell Crosslinked Micelles below the Critical Micelle Concentration

To explore the potential of shell crosslinked micelle (SCM) as a drug carrier, the drug release behavior of poly(ε-caprolactone)-b-poly(acrylic acid) (PCL-b-PAA) SCMs was investigated. PCL-b-PAA was synthesized by ring opening polymerization of ε-caprolactone and atom transfer radical polymerization oftert-butyl acrylate, followed by selective hydrolysis oftert-butyl ester groups to acrylic acid groups. The resulting amphiphilic polymer was used to prepare SCMs by crosslinking of PAA corona via amidation chemistry. The drug release behavior of the SCMs was studied, using pyrene as a model drug, and was compared with that of non-crosslinked micelles, especially below the critical micelle concentration (CMC). When the shell layers were crosslinked, the drug release behavior of the SCMs was successfully modulated at a controlled rate compared with that of the non-crosslinked micelles, which showed a burst release of drug within a short time.

Synthesis of 4-tert-butyldimethylsilyloxystyrene and its copolymerization with styrene using (η5-indenyl)trichlorotitanium in the presence of methylaluminoxane

Poly(styrene-co-4-tert-butyldimethylsilyloxystyrene) as a precursor of hydroxyl-functionalized syndiotactic polystyrene was successfully synthesized via (η5-indenyl)trichlorotitanium (IndTiCl3)-catalyzed copolymerization of styrene with 4-tert-butyldimethylsilyloxystyrene in toluene at 25°C in the presence of methylaluminoxane (MAO) ([Al]/[Ti] = 2 000). The amount of styrene derivative incorporated into the polymeric chain for a 20,7 : 1 mole feed ratio of styrene to 4-tert-butyldimethylsilyloxystyrene was found to be 1,8 mol-% from a 1H NMR analysis. The styrene derivative was successfully prepared from 4-hydroxybenzaldehyde via first protecting the hydroxyl group using tert-butyldimethylchlorosilane followed by the ‘Wittig-type’ reaction with the ‘Tebbe’ reagent. The yield was about 82 wt.-% on the basis of the initial amount of 4-hydroxybenzaldehyde used.

A novel water-soluble and self-doped conducting polyaniline graft copolymer

A water-soluble and self-doped conducting polyaniline graft copolymer, poly(styrenesulfonic acid-g-aniline) (PSSA-g-PANI), was first synthesized and its electrical properties were investigated.

Effect of molecular architecture on micellization, drug loading and releasing of multi-armed poly(ethylene glycol)-b-poly(ε-caprolactone) star polymers

This study investigated the effect of molecular architecture of amphiphilic star polymers on micelle formation and drug loading and releasing. For this, multi-armed star block copolymers having poly(ethylene glycol) as a hydrophilic block and poly(ε-caprolactone) as a hydrophobic block were synthesized by using a divergent synthetic method consisting of a coupling reaction and a ring opening polymerization. The molecular weight and molecular weight distribution of the block copolymers were characterized by 1H NMR and GPC measurements. Dynamic light scattering and fluorescence spectroscopic analysis were employed to observe micellization, drug loading, and drug release behaviors. We have figured out that the number of arms is a critical factor that changes critical micelle concentration as well as drug loading and releasing behaviors; increase in the number of arms not only led to lowering the critical micelle concentration and drug release rate but also increased the micelle size and drug loading efficiency.

Studies on polymer-metal interfaces, 3. An analysis of interfacial characteristics between amine-functionalized polystyrene/copper and between hydroxyl-functionalized polystyrene/copper

The interfacial characteristics between amine-functionalized polystyrene/copper and between hydroxyl-functionalized polystyrene/copper were investigated by adhesion strength measurements and reflection absorption infrared (RAIR) spectroscopy. Poly(styrene-co-4-aminostyrene) (PS-NH2) and poly(styrene-co-4-hydroxystyrene) (PS-OH) containing ca. 1.5 and 1.7 mol-% of comonomers, respectively, were synthesized by anionic polymerization. The adhesion strength between PS-OH and copper is higher than that between PS-NH2 and copper. The analysis with RAIR spectroscopy shows that both the NH2 group in PS-NH2 and the OH group in PS-OH interact specifically with the copper surface. RAIR spectroscopy also shows that the OH group in PS-OH is oriented in a parallel direction to the copper surface and that the C—O bond is oriented in a direction slightly inclined from the normal surface. The NH2 group in PS-NH2 has two orientations, while the orientation of the C—N bond could not be identified precisely from the RAIR spectrum.

Effect of chain architecture of graft copolymer on the structure of adsorbed layer: a Monte Carlo simulation approach

The effect of chain architecture of graft copolymer on the structure of an adsorbed layer on a surface is investigated using an off-lattice Monte Carlo simulation method. The graft copolymers used for the simulation have the same composition but different chain architecture. The simulation results show that the layer thickness of multi-chains adsorbed onto the surface first decreases with increasing the number of side chains, indicating that the chain conformation of the adsorbed polymer becomes more flattened as the length of the side chain becomes shorter. When the length of the side chain decreases further than a critical length, however, a slight increase in layer thickness is observed, accompanied with an increase in the population of loosely bound chains.