Polymers - Vol. 58, No. 2 (February, 2009)

Hot Topics

Vol. 58, No. 2 (February, 2009)

Liquid-Crystalline Semiconductors and Their Application to Thin-Film Transistors
School of Engineering, The University of Tokyo

Carrier transport in liquid crystal phases, material design of liquid crystalline semiconductors with the high carrier mobility, and their application to field-effect transistors are studied. High carrier mobility has been observed in the smectic phases of oligothiophene derivatives as well as in the columnar phases of triphenylene and hexabenzocoronene derivatives. The mobility increases with an increase in the molecular ordering in the mesophases and extension of p-conjugated systems of the liquid crystal molecules. Asymmetrically substituted liquid crystalline oligothiophene derivatives are solution-processable and can be applied to field-effect transistors which exhibit high performance. Polymer Preprints, Japan 2008, 57, 2197.

 Progress on Color E-Paper Using Organic-Metallic Hybrid Polymers
Masayoshi HIGUCHI
WPI Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), and PRESTO, JST
Colorization is now one of the most important research subjects in electronic paper (E-paper) and an electrochromic method has a potential to achieve it. Organic-metallic hybrid polymers are a new electrochromic material (Figure c) and the metal-to- ligand charge transfer (MLCT) absorption in the polymers is controlled by electrochemical redox (reduction and oxidation) of the metal ions (Higuchi et al. Chem. Rec. 2007, 7, 203). An electrochromic solid-state device using the organic-metallic hybrid polymer bearing both iron(II) and ruthenium(II) ions exhibits multi-color changes by changing the applied voltage (Figure a). A large display (10 inch size) using the organic-metallic hybrid polymer is also fabricated (Figure b). Polymer Preprints, Japan 2008, 57, 2194.

Molecular, Structural, and Material Design of Bio-Based Polymers
Yoshiharu KIMURA
Deptartment of Molecular Engineering Kyoto Institute of Technology
Polymeric materials prepared from renewable resources are now being accepted as Òbio-based polymersÓ. We developed new synthetic routes to bio-based polymers such as polylactides (PLA), poly(butylene succinate) (PBS) and their copolymers. Particularly, we focused on the stereoblock polylactides (sb-PLA) consisting of different PLLA/PDLA sequence ratios, because they can preferentially form stereocomplex crystals showing higher melting temperature. These novel sb-PLA polymers having high performance were named ÒNeo-PLAÓ. The enantiomeric PLA molecules form various helical conformations in crystallization by which the structure and properties are changed. We discovered an interesting doubly coiled conformation in a nano-band structure formed by block copolymers. Polymer Preprints, Japan 2008, 57, 2188.

Preparation of Smart Soft Materials Using Molecular Complexes
Takashi MIYATA
Faculty of Chemistry, Materials and Bioengineering, Kansai University
We have prepared a variety of biomolecule-responsive gels that undergo volume changes in response to target biomolecules. This paper describes two types of biomolecule-responsive gels prepared by using biomolecular complexes such as antigen- antibody complexes, saccharide-lectin complexes and DNA duplexes as reversible crosslinks. One is a biomolecule-crosslinked gel and the other is a biomolecule-imprinted gel. The biomolecule-crosslinked gels (glucose-, antigen- and DNA-responsive gels) can swell in the presence of a target biomolecule due to the dissociation of biomolecular complexes that play a role as reversible crosslinks. On the other hand, biomolecule-imprinted gels (endcrine disruptor-, tumor marker glycoprotein-, and DNA-responsive gels) can shrink in response to a target biomolecule due to the complex formation between ligands and the target molecule. Thus, biomolecule-responsive gels have many potential applications as smart soft materials in various fields. This paper focuses on synthetic strategy of biomolecule- responsive gels and their responsive behavior. Polymer Preprints, Japan 2008, 57, 2182.

Development of the Small-Diameter Vascular Grafts Based on Silk Fibroins from Transgenic Silkworm for the Vascular Regeneration
Yasumoto NAKAZAWA, Rui TAKAHASHI, Keisuke YAGI, Shizuo YAMAZAKI, Chiyuki TAKABAYASHI, Souichirou ENOMOTO, Masataka SATA, Kan KAJIMOTO, Hiroyuki DAITA, Katsumi MIYAUCHI, and Tetsuo ASAKURA*
Graduate School of Engineering, Tokyo University of Agriculture and Technology
In the field of surgical revascularization, the need for functional small-diameter (1.5Ð4.0mmf) vascular grafts is increasing. Several synthetic biomaterials have been tested for this purpose, but in many cases they cause thrombosis. Thus, there is a lot of interest in research of new materials for artificial vascular grafts recently. In this study, we evaluated the potential of silk fibroin to generate artificial vascular prosthesis for small arteries. The newly developed vascular grafts made from silk fibroin showed a good patency, and these grafts were commonly covered with cells at 4 weeks after implantation. These results suggest that this new silk fibroin graft provides an anti-thrombotic surface and a good scaffold for various types of cells to attach and proliferate. In combination with improved biological function such as cell adhesion, which is introduced by gene modification in silkworms, silk will be applicable for development of new vascular grafts. Polymer Preprints, Japan 2008, 57, 5136.

High-strength hydrogel with super homogeneous network structure
Takamasa SAKAI
Department of Material Engineering, Graduate School of Engineering,
University of Tokyo
As a new class of high-strength hydrogels, we designed a Tetra-PEG gel by combining two symmetrical tetrahedron-like macromonomers of the same size. Because the nano-structural unit of the gel network was defined by the tetrahedral PEG arm, the gel had a homogeneous structure and resultant high mechanical strength comparable to that of native articular cartilage. Furthermore, since the gel was formed by mixing two biocompatible macromonomer solutions, the gelation reaction itself and the resultant gel were also biocompatible. Small angle neutron scattering showed that no inhomogeneities existed in the network. Thus, we successfully designed and fabricated a high strength hydrogel by controlling the homogeneity of network structure for the first time, which will lead to multiplied effects. Polymer Preprints, Japan 2008, 57, 4572.

A New Triple Helical Complex Consisting of One Polynucleotide and Two Polysaccharide Chains and its application to gene carrier Kazuo SAKURAI
Department of Chemistry & Biochemistry, The University of Kitakyushu
Schizophyllan is a polysaccharide that belongs to the b-(1®3)- glucan family and adopts a triple helix conformation in water. We found that when single chain of SPG and single-stranded polynucleotides are mixed, a helical complex is formed consisting of two s-SPG chains and one nucleotide chain. Since b-(1®3)- glucan can be recognized by antigen presenting cells with a receptor called dectin-1, the bound polynucleotides can be ingested into the cells. Polymer Preprints, Japan 2008, 57, 2191.

Mid-Temperature Polymer Electrolyte Fuel Cell using Basic Polyelectrolyte/H3PO4 Membranes
Yuko TAKEOKA*, Hiroki OHMORI, Masahiro FUJITA, and Masahiro RIKUKAWA
Department of Materials and Life Sciences, Sophia University
The mid-temperature polymer electrolyte fuel cells (MT-PEFCs) that operate above 120 ¡C without humidification have been considered to provide many advantages including fast electrode kinetics, high tolerance to fuel impurities, and simplified system designs. Phosphoric acid doped basic polyelectrolytes such as poly(benzimidazole) (PBI) are attractive candidates for MT-PEFCs because of their excellent thermal stability and high proton conductivity at high temperatures and anhydrous state. In order to improve the low temperature performance, poly[2,2-(2,6-pyridine)-5,5- bibenzimidazole] (PyPBI) was synthesized. The increase in basicity of polymer promoted high phosphoric acid doping level and high proton conductivity. PEFC performance of PyPBI/H3PO4 complex (3.76 mol unitÐ1) was higher than that of PBI/H3PO4 complex (2.52 mol unitÐ1). By optimizing the cell conditions, PyPBI /H3PO4 and PBI/H3PO4 can be operated even at room temperature. Polymer Preprints, Japan 2008, 57, 4011.

New Naturally Occurring Monomer Unit for Bacterial Polyesters
Takeharu TSUGE
Department of Innovative and Engineered Materials, Tokyo Institute of Technology
We demonstrated that bacterial polyester (polyhydroxyalkanoate, PHA) synthesized from sugars by the recombinant strain contains a new monomer unit, 3-hydroxy-4-methylvalerate (3H4MV), which has a methyl-branch in the side chain, in addition to the dominant 3-hydroxybutyrate (3HB) unit. A couple of organic acids was found to function well as a 3H4MV precursor and enhanced 3H4MV incorporation into P(3HB-co-3H4MV). The newly identified 3H4MV unit would be a promising monomer for improving material properties of 3HB-based copolymers. Polymer Preprints, Japan 2008, 57, 5308.

Nanostructured Colloidal Arrays in an Ionic Liquid
Akihiko TANIOKA*, Hidetoshi MATSUMOTO, Department of Organic and Polymeric Kazuhide UENO, Yuta SANO, Aya INABA, and Masayoshi WATANABE*
Department of Chemistry and Biotechnology, Yokohama National University
We developed novel nanostructured colloidal arrays (NCAs) showing mono-chromatic structural colors in an ionic liquid. It was found that the intriguing optical properties such as homogeneous, non-iridescent, and angle-independent structural colors are due to the short-range ordered periodic structures of the colloidal array in the ionic liquid. The color of NCAs can be precisely controlled over the entire range of visible region by adjusting the particle content. Furthermore, the NCAs are soft gel materials with shear thinning behavior and possess high ionic conductivity. The NCAs in ionic liquids may allow the development of novel photonic materials and electrochemical devices. Polymer Preprints, Japan 2008, 57, 3457.

Development of S-Glycosylated Chlorins as Unprecedented Powerful Photosensitizers for Photodynamic Therapy
Shigenobu YANO* and Makoto OBATA**
Innovative Collaboration Center, Kyoto University* Graduate School of Humanities and Sciences, Nara WomenÕs University**
Recently much attention has been focused to photodynamic therapy (PDT) as clean and new modalities of selective treatments of cancer. In general, PDT damages not only cancer or tumor tissue, but also normal tissue. For this reason, it is required to use photosensitizer which can exhibit photocytotoxicity in the smallest possible quantity. We have newly prepared 5, 10, 15, 20- tetrakis [4-(b-D-glucopyranosylthio)-2, 3, 5, 6-tetrafluorophenyl]-2, 3-[methano (N-methyl)iminomethano] chlorin (abbr. TFPC-SGlc) and 5, 10, 15, 20- tetrakis[4-(b-D-galactopyranosylthio)-2, 3, 5, 6-tetrafluorophenyl]-2, 3- [methano(N-methyl)iminomethano]chlorin (abbr. TFPC-SGal), (Fig. 1). Photocytotoxicities of TFPC-SGlc and TFPC-SGal were tested in HeLa cells using light of wavelength over 500 nm. At the drug concentration of 0.09 mM, there existed significant difference between TFPC-SGlc and TFPC-SGal {Fig. 2-(c); TFPP: tetra(fluorophenyl) porphyrin, TFPC: tetra(fluorophenyl) chlorin}. It was found that S-glycosylated chlorin derivatives for which D-glucose was linked as a sugar exhibited higher photocytotoxicity than the derivative for which D-galactose was linked, TFPC-SGlc is about 300 times more powerful than Laserphyrin¨ Thus, we have succeeded in the construction of the unprecedented powerful photosensitizer for photodynamic therapy Polymer Preprints, Japan 2008, 57, 2821.

Design of Stable Radical-Containing Nanoparticles (RNP) for Anti-oxidative Stress Drug
TIMS, University of Tsukuba
Oxidative stress is a pathogenesis of cerebral ischemia-reperfusion. After the reperfusion, reactive oxygen species (ROS) are generated, which can cause further tissue injury. The prevention of reperfusion injury is essential to minimize a degree of cerebral infarction. A 2,2,6,6- tetramethylpiperidinyloxy (TEMPO), which has a stable radical, is one of promising compounds as a scavenger of ROS. However, TEMPO is hard to utilize in vivo due to a preferential renal clearance and a rapid reduction. Recently, we have developed radical-containing nanoparticle (RNP), which contains several thousand radicals in the core, using self-assembling of amphiphilic block copolymer composed of a hydrophilic poly(ethylene glycol) (PEG) segment and a hydrophobic poly(chloromethylstyrene) (PCMS) segment possessing TEMPO units as a side chain. Our idea is to use the RNP as anti-oxidative stress drug. To investigate whether the RNP reduces the injury caused by cerebral ischemia-reperfusion, the RNP was injected intravenously from a rat vein in 30 min after reperfusion. Consequently, the RNP significantly reduced the injury, which is promising as high performance nanoparticle for anti-oxidative stress drug. Polymer Preprints, Japan 2008, 57, 4934.