Articles in 2014

Network structure of syndiotactic-polystyrene (sPS) or syndiotactic-poly(styrene-co-4-R-styrene) (St/RSt) -organic solvents gels has been quantitatively studied by means of a scanning microscopic light scattering (SMILS). The SMILS analysis cleared that most of the gels showed relaxation peaks derived from small mesh size ~0.6–1.8 nm and large cluster structure ~1000–6000 nm, and a gel formation model was proposed based on the analysis. Interaction between R groups (R=OH, antracenecarbonyl) affected the network structure of the gels.

This review focuses on the development of donor–acceptor semiconducting polymers using electron-deficient π-building units, such as thiazolo[5,4 -d]thiazole, benzo[1,2-d:4,5-d′]bisthiazole, naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole and thieno[3,2-b]thiophene-2,5-dione. All of the polymers form crystalline structures in thin films and possess deep highest occupied molecular orbital energy levels; consequently, the polymers demonstrate high charge carrier mobilities with high air stability. Several key parameters were identified that must be taken into account when designing high-performance polymers: the symmetry of the building units, backbone shape, and delocalization of the π-electrons along the backbone.

The binding conformation of aspartic acid (Asp) at the calcite surface is strongly affected by the structure of the surrounding water. On the {104} plane, Asp binds directly to the acute step edge, but not to the obtuse step edge, reflecting a difference in the structure of water near the step edge. This selective binding to the acute step edge causes a change in the step morphology on the {104} plane when Asp is added to real systems.

Titanium dioxide (TiO₂) with highly controlled nano (polymorph) and macro (morphology) structures was synthesized from water by hydrothermal method using a series of unique water-soluble titanium complexes. Thanks to their high stability in water, a variety of organic molecules, which act as a shape-controlling agent, can coexist, resulting in the formation of anistropically grown rutile-type TiO₂. The obtained rutile crystals exhibited greatly improved functions with respect to their dielectric or photocatalytic performance. The results suggest that the chemical design of metal-complex precursors leads to achievement of high functionalization of materials.

An end-grafted flexible diblock copolymer exists a critical adsorption point T_c from a desorbed state to an adsorbed state. The finite-size scaling law is adopted to determine T_c and the crossover exponent φ. The non-adsorbed block B weakens the adsorption of the adsorbed block A. Then the effective influence of the B block is reduced with increase in the length of the A block but it is independent of the length at T_c.

Half-metallocene complexes of the type CpM(L^L)X₂ (L^L=chelating ligands) offer the advantage of catalyst modification: by changing one cyclopentadienyl ligand of metallocene complexes to other ligands such as three-, four-, five-, six- and seven-membered chelates, bidentate and tridentate coordination, and monoanionic, dianionic and trianionic system, steric and/or electronic modification of the coordination environment is much flexible. The structural uniqueness of the metal complexes and the effects of the chelate ring sizes on their productivity and activation processes of the metal complexes with cocatalysts are highlighted.

Germylenes (1a and 1b) reacted with p-quinoneimine (2) to give copolymers (3a and 3b) having a tetravalent germanium unit and a p-aminophenol unit, alternatively. The copolymerization took place at 0°C smoothly without added catalyst or initiator. 1 acted as a reductant monomer whereas 2 as an oxidant monomer (oxidation-reduction alternating copolymerization). Soluble copolymers were obtained in very high yields, having high molecular weight. ESR spectroscopic studies of the reaction suggested a structure of stable germyl radical and a biradical copolymerization mechanism.

Highly stretchable hydrogel shows actuation behaviour upon irradiation of infrared (IR) light. The photothermal effect induced by heat from IR absorption causes cooperative change in the network alignments in the stretched sample.

Long-time measurements on the glass transition of polystyrene thin films supported on Si substrates were performed at various heating rates using X-ray reflectivity. Reconstructed depth profiles of thermal expansivity were obtained by fitting via an integral model, which indicated that the length scale of the interfacial dead region decreases with decreasing heating rate, whereas the thickness of the mobile surface layer increases.

Photocrosslinkable polymers and UV-curable resins are significant materials in relation to the industrial applications for coatings, adhesives, photoresists and printing plates. Recently, much attention has been paid to recovery or recycling of crosslinked polymers due to the environmental regulations. This article reviews our recent research work on the synthesis, properties and applications of photocrosslinkable polymers and UV-curable resins with degradable property.

The long-term thermal stability of the attenuation of graded-index plastic optical fibers is strongly dependent on whether the glass transition temperature (T_g) of the cladding layer is higher than the environmental temperature. When fibers are exposed to temperatures higher than both the core and cladding T_g values, the core-cladding boundary fluctuates spatially and scatters light. However, our study indicates that the core is not necessarily required to be in a glassy state to maintain a flat, smooth interface as long as the cladding is in a glassy state.

Alkyl imidazolium-based polymer hydrogels produced by copolymerizing N-allylimidazolium chloride (AlImCl) bearing a long alkyl chain exerted a sol-gel phase transition in response to the addition of specific anions. Microscopic observation indicates that spherical microdomains of the polymer assembly were formed in the hydrogels. A hydrophobized fluorescent dye spontaneously accumulated and freely moved in the microdomains due to their high hydrophobicity and fluidity. The hydrogels with the unique domains are promising supports that can be used for multiple functional molecules in biosensing, bioproduction and a new type of drug delivery system.

Novel core/shell-like structured ultrafine branch nanofibers were successfully fabricated by a phase-separation process using simple polymer blend (polyacrylonitrile (PAN) and fluorinated polyimide (PI)) solutions with electrospinning. The obtained core/shell-like structured branch nanofibrous membranes showed strong hydrophobicity based on the hydrophobic shell polymer and ultrafine branch nanostructures. This simple process could be used to prepare core/shell structured branch nanofibers composed of other blend polymers and would also provide novel opportunities for industrial applications, such as nanocoating, nanoreinforcement, nanocomposite, nanomedicine and a drug-release system.

Ring-opening polymerization (ROP) of ɛ-caprolactone with dilithium tetra-tert-butylzincate (TBZL) in toluene was performed. The initiating species for the ROP of ɛ-caprolactone is not the tert-butyl anion of TBZL but the hydroxyl anion derived from a trace amount of H₂O or alcohol. Poly(ɛ-caprolactone) with a BnO group at the initiating chain-end was obtained by adding benzyl alcohol as an initiator, as expected. The molecular weight distributions were relatively narrow, except with increased temperatures and/or prolonged polymerization times. This system does not need a high polymerization temperature or long polymerization time.

Die-bonding film is widely applied for semiconductor package of electronic equipments. The die-bonding film based on epoxy resin/acrylic polymer system shows the higher flexibility to thermal stress during the heat cycle test compared with epoxy–matrix systems. In addition, properties of the film vary widely depending on the ratio of epoxy resin and acrylic polymer contents. To satisfy the target properties, novel material design method named weak conditioned combinatorial linear programming was developed.

Self-assembled organic nanotubes (S-ONTs) from rationally designed synthetic amphiphiles provide a variety of inner and outer surfaces as well as homogeneous hollow cylinders with precisely controlled inner diameters. Focusing on distinctive characteristics of the nanospace or nanochannel, we review the recent progress in the research on encapsulation, transportation, stabilization and release behavior of biomacromolecules in the S-ONT nanochannels in terms of application to a bioengineering field.

Low-molecular-weight compounds, which form physical gels, are called ‘gelators’ and have received a great amount of scientific and technological interest. The physical gelation by gelator results from non-covalent bonds, represented by hydrogen bond. Molecules of gelator are first self-assembled in cooling process, producing fibrous assemblies. Then, these fibrous assemblies form a three-dimensional network structure, and gelation occurs by trapping solvent in the networks. Fibrous assemblies can be observed by electron microscope. This is a transmission electron microscopy image of tetrachloromethane gel formed by N-octadecylamide of N-benzyloxycarbonyl-L-isoleucine.

Ulva can overgrow and result in green tides around the world. It forms algal mats on the Wajiro tideland in Japan. The major polysaccharide of Ulva is ulvan, a sulfated glucurono-rhamno-xyloglycan. Ulvan was modified with three diisocyanate derivatives to yield urethane foam and its ability to remove Cu(II) ions from an aqueous solution was investigated. Notably, the foam could remove up to 72.7% of Cu(II) ions.

Bio-based amphiphilic polymers having a helical hydrophobic unit have been extensively studied on molecular assemblies and their morphology. Molecular assemblies having complex morphologies could be prepared by using the specific characters of the helical unit, and the unique self-assembling methodology was named as ‘patchwork self-assembling’. Further, application of the obtained molecular assemblies in medicinal fields was examined. Lactosome was accumulated at the targeted tumor region by the EPR effect, and therefore, expected to be an excellent nano-ordered carrier for drug and/or imaging agent delivery.

This review introduces recent attempts in the photoalignment processes of liquid crystalline polymers focusing on the two aspects. First, the strategies to ensure effective in-plane alignment of the photoresponsive mesogens are summarized. Despite many investigations reported so far, the film systems have not been optimized for efficient photoreaction. Second, new photoalignable systems involving block copolymer frameworks such as surface-grafted polymers and block copolymer thin films are introduced. The photoalignment processes in such mesoscopic systems involve strong cooperative motions among different hierarchical size features. Based on these approaches, a new strategic platform, photoalignment via a command surface at the free surface, is further proposed.