Kyung-Min Kim

Polymer hybrids of functionalized silsesquioxanes and organic polymers utilizing the sol-gel reaction of tetramethoxysilane

The ternary polymer hybrids were prepared by organic polymers such as poly(2-methyl-2-oxazoline) (POZO) or poly(N-vinylpyrrolidone) (PVP) and aminopropylsilsesquioxane (Cube-aminopropyl) utilizing the sol–gel reaction of tetramethoxysilane (TMOS). The prepared polymer hybrids were characterized by IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), 1H NMR, scanning electron microscopy (SEM), etc. In this hybrid system, hydrogen-bonding interactions played a critical role in the formation of the transparent polymer hybrids. Polymer hybrids using POZO showed high transparency and homogeneity in a wide range of the feed ratios of POZO to Cube-aminopropyl. On the other hand, in case of polymer hybrids using PVP, higher Cube-aminopropyl ratio brought about the phase separation, indicating the aggregation of the Cube-aminopropyl itself. The homogeneity of ternary polymer hybrids was found to be closely dependent on the difference between strength of hydrogen bonding interaction of polymer and residual silanol groups of silica gel and strength of that of polymer and Cube-aminopropyl. It is also observed that initial decomposition temperature of polymer hybrids was increased with increasing the Cube-aminopropyl ratio.

Organic-inorganic hybrid gels having functionalized silsesquioxanes

Hybrid terpolymers consisting of polyhedral oligomeric silsesquioxanes (POSS), N,N-dimethylacrylamide, and bipyridine monomer were synthesized by a common radical polymerization method and their structures and thermal properties were studied by FT-IR, 1H NMR, DSC, TGA. The thermal stabilities of the hybrid terpolymers increased on increasing the content of POSS in the feed ratio. New hybrid gels containing POSS were prepared through the coordination of various metal ions to 2,2′-bipyridine-modified hybrid terpolymers. Highly concentrated solutions of terpolymers with iron(II) sulfate or ruthenium(III) chloride gave hybrid gels in good yields. On the other hand, no hybrid gel was formed with nickel(II) chloride even at much higher concentrations of nickel ions due to rapid ligand exchange reactions causing the polymer network to disappear as a result of a change in the nature of the coordination bonds from an intermolecular network to an intramolecular network. The degree of swelling and the thermal stability of the gels in various solvents were dependent on the content of POSS moiety in the hybrid gel and the ruthenium gel was considerably more stable than the iron and nickel gels. The hybrid gels containing POSS had properties characteristic of hydrogels as well as those of lipogel depending on the content of POSS in the hybrid gel. By analysis of the degree of swelling, it was concluded that the amount of POSS moiety in the hybrid gel has a significant effect on the degree of swelling in this system.

Preparation of hydrophobic CaCO3 composite particles by mineralization with sodium trisilanolate in a methanol solution

Hydrophobic CaCO3 composite particles were prepared via crystallization of CaCO3with a sodium trisilanolate [(c-C5H9)7Si7O9(ONa)3] in methanol. The molar ratio of calcium ion to the sodium trisilanolate was varied from 0.1 to 0.5. FT-IR and TGA analysis of the obtained product indicated that the trisilanol was bound to the crystalline CaCO3. By changing the concentration of the trisilanol, composite particles with different shapes and polymorphism were obtained. Low concentration of the trisilanol gave stable vaterite crystals, the polymorph of which did not change when the composite was kept in water for more than 1 week. The contact angle of the modified vaterite was 62±4°. Dispersability of the composites in a polystyrene matrix was significantly improved compared with a bare CaCO3. We have succeeded in surface modification of particles with the hydrophobic trisilanolate.

An Efficient Method for Synthesis of PEO-Based Macromonomer and Macroinitiator

Then-butyllithium-initiated ring-opening polymerization of ethylene oxide, in a mixture of benzene and dimethylsulfoxide (DMSO), between 25-45°C, with potassiumtert-butoxide, is a useful and powerful method to control the molecular weight as well as achieve a quantitative chain-end functionalization yield of the resulting polymeric alkoxidevia a one pot synthesis. The molecular weight of the product could be controlled by adjusting the ratio of grams of monomer to moles of initiators, such asn-butyllithium ([n-BuLi]) and potassiumt-butoxide ([t-BuOK]). The yields for the macromonomer and?-brominated poly(ethylene oxide) (PEO) were quantitative in relation to the chain-end functionalizations of the polymeric alkoxide formed. The resulting products were characterized by a combination of1H-NMR spectroscopic and size exclusion chromatographic analyses.

Polymer-Coated Tips for Patterning of Viruses by Dip-Pen Nanolithography†

Methods have recently been developed to allow the study of protein–protein and cell–surface interactions on a molecular level. These techniques rely on nanoscale arrays for highthroughput analysis of biological functions. Researchers working in areas including biosensors, biodiagnostics, genomics, proteomics, cytology, materials science, and general chemistry have benefited from these advances. To further drive this technology, high-precision patterning techniques are necessary to allow a wider range of biomolecules to be deposited onto a substrate. A variety of methods including UV lithography, electron-beam lithography, contact printing, nanoimprinting, and scanning probe lithography have been used to deposit biomolecules on various surfaces with nanometer accuracy. One such technique is dip-pen nanolithography (DPN). DPN is a scanning probe lithography method based on atomic force microscopy (AFM). Using DPN, nanostructure patterns of extraordinary complexity can be created. This technique has potential applications for gene chips and multiple biomolecular arrays because one can create patterns with numerous molecules in a directwrite fashion. The driving force of DPN for transporting materials is molecular diffusion through the water meniscus formed between the AFM tip and the surface. Although DPN provides a simple and efficient method to deposit DNA, peptides, and proteins on surfaces at nanoscale resolution, most DPN methods struggle with higher-molecular-weight biomolecules. Molecules larger than 15 nm (the maximum size of most immunoglobulin G proteins) are not efficiently transported through this water meniscus. Recently, many strategies have been employed to solve this problem by modifying tip surfaces, and by adding carrier materials to ink solutions. For example, Mirkin and co-workers published a description of a polymer-pen lithography (PPL) method, in which elastomeric tips without cantilevers are used to deliver ink solutions. These tips, which are made entirely of poly(dimethylsiloxane) (PDMS), make it possible to control feature sizes by varying the tip–substrate contact time and contact force. However, no general methods have been developed that would allow the direct-write DPN technique to create patterns of large-sized biomaterials such as viruses. Herein, we describe a novel and effective method for fabricating porous polymer-coated AFM tips, which overcome the shortcomings of DPN, such as the difficulty of transporting large bioparticles and the limited amount of ink solution that can be delivered. Using this tip, we have generated patterns of adeno-associated viruses (AAVs). Our approach uses a nanoporous poly(2-methyl-2-oxazoline) (PMeOx)-coated tip (Scheme 1). A bare SiO2 AFM tip was first modified with 11-iodoundecyltrichlorosilane as an initiator through a silanization reaction. This active layer was then used to initiate the ring-opening polymerization of 2methyl-2-oxazoline monomer, which resulted in the formation of nanopore network structures. A typical scanning electron microscopy (SEM) image of the fabricated PMeOxcoated tip shows that the pore sizes ranged from 50 nm to a few hundred nanometers (Figure 1a). The AFM image of PMeOx, taken under ambient conditions, showed similar nanopore structures (Figure S1 in the Supporting Information). PMeOx is a well-characterized, hydrophilic, biocompatible, and water-soluble nonionic polymer that is often used for drug delivery. A variety of PMeOx hydrogels can be formed by chemically cross-linking a hydrophilic polymer matrix through covalent bonds or by physically cross-linking with hydrogen bonds. In our method, when the PMeOx-coated AFM tip is brought into contact with an aqueous ink solution, the surface-immobilized porous polymer layer absorbs the ink solution and forms a swollen hydrogel. Because the AAV used [*] Y.-H. Shin, S.-H. Yun, S.-H. Pyo, Y.-S. Lim, H.-J. Yoon, K.-H. Kim, Prof. K.-M. Kim, Prof. J.-H. Lim Department of Polymer Science and Technology Chungju National University 72 Daehangno, Chungju-si 380-702 (Korea) Fax: (+ 82)43-841-5420 E-mail: jhlim@cjnu.ac.kr

Hybrid Nanocomposites of Palladium Nanoparticles Having POSS and MWNTs via Ionic Interactions

Palladium nanoparticles having cubic silsesquioxanes (POSS) (Pd-POSS) were produced by the reaction of palladium (II) acetate and octa(3-aminopropyl)octasilsesquioxane octahydrochloride (POSS-NH3+) in methanol at room temperature. Functionalized multiwalled carbon nanotubes (MWNT-COOH) were prepared by acid treatment of pristine MWNTs. The hybrid nanocomposites of Pd-POSS and MWNT-COOH (Pd-MWNT nanocomposites) were synthesized by self-assembly method via ionic interaction between positively charged Pd-POSS and negatively charged MWNT-COO−. The spherical aggregates of Pd-POSS with a diameter of 40–60 nm were well attached to the surfaces of MWNT-COOH on Silicon wafer. The composition, structure, and surface morphology of Pd-MWNT nanocomposites were studied by UV-vis spectrophotometer, energy dispersive spectrum (EDX), scanning electron microscopy (SEM), and atomic force microscope (AFM).

Synthesis of new pH-sensitive amphiphilic block copolymers and study for the micellization using a fluorescence probe

This paper reports a facile synthesis of new water-soluble poly(ethylene oxide) (PEO)-based amphiphilic block copolymers showing pH sensitive phase transition behaviors. The copolymers were prepared by atom transfer radical polymerization (ATRP) of methacrylamide type of monomers carrying a sulfonamide group using a PEO-based macroinitiator and a Cu(I)Br/Me6TREN catalytic system in aqueous media. The resulting polymers were characterized by a combination of1H-NMR, size exclusion chromatography, and UV/Visible spectrophotometeric analysis. The micellization of the block copolymers as a drug-loading mechanism in aqueous media using fluorescein salt was examined as a function of pH. The stable micelle formation and its loading efficacy suggest that the block copolymers can be used as precursors for drug-nanocontainers.

Synthesis and characterization of transparent poly(2-methyl-2-oxazoline)(POZO)–vanadium oxide (V2O5) hybrids with reversible formation

Optically transparent and homogeneous polymer hybrids of poly(2-methyl-2-oxazoline) (POZO) and vanadium oxide (V2O5) can be prepared by utilizing the hydrogen bonding interactions between the amide groups of POZO and V–OH groups formed in the hydrolysis of vanadium(V) oxytripropoxide (TPVO). POZO acts as a stabilizer in the sol–gel reaction of TPVO, since this sol–gel reaction is too fast to obtain a transparent film without POZO. The amorphous state of the POZO–V2O5 hybrid was confirmed by DSC, SEM, and XRD. The polymer hybrids obtained can be reversibly dissolved in the solvents and cast again because of the amorphous state of vanadium(V) oxide. Moreover, the solubility of the polymer hybrids was dramatically changed by the reduction of V2O5 from V(V) to V(IV).

Fabrication of hybrid nanocomposites of poly(acrylic acid)-grafted MWNTs and spherical aggregates of palladium nanoparticles with POSS

In this report, hybrid nanocomposites were fabricated by poly(acrylic acid)-grafted multiwall carbon nanotubes (MWNTs) (PAA-grafted MWNTs) and spherical aggregates of palladium nanoparticles with cubic silsesquioxanes (Pd-POSS) through ionic interactions. The modification of MWNTs with PAA via in situ radical polymerization and self-organization of palladium nanoparticles by cubic silsesquioxanes (POSS) introduced negative and positive charge on the surface of MWNTs and Pd-POSS, respectively. Through electrostatic interactions, the positively charged Pd-POSS was physically attached to the surface of negatively charged PAA-grafted MWNTs. Pd-POSS were more densely and continuously deposited on the surface of PAA-grafted MWNTs than MWNTs-COOH due to the polymer effect. The characteristics of the hybrid nanocomposites were characterized by 1H-NMR, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, field-emission scanning electron microscopy, atomic force microscope, and energy dispersive spectrum.

Preparation and Characterization of Expanded Graphite Intercalation Compound/ UV-Crosslinked Acrylic Resin Pressure Sensitive Adhesives

The expanded graphite intercalated compound (xGIC)/pressure sensitive adhesives (PSAs) were prepared by syrup process and in situ process. The effects of xGIC filler on the morphology and property of acrylic resin based UV-crosslinked PSA were investigated. The xGICs showed more uniform dispersion in acrylic matrix and the degree of filler connection was more prominent in the syrup process than in situ process. The peel strength and tackiness of UV-crosslinked PSAs were strongly dependent on the amount of the filler and the peel strength decreased with increasing xGIC. The thermal conductivity of PSAs was explained in terms of filler dispersion, wetting, and matrix infiltration. The thermal conductivity of PSA was 0.46 W/mK by adding 20 wt% of xGIC, which was 287% improvement compared to the unfilled PSA. It is speculated that 2-dimensional xGIC fillers effectively formed the thermal pathway.