Articles in 2014

Polypropylene with low isotacticity and high molecular weight is synthesized using specific C₂-symmetric doubly bridged metallocene complexes. This polymer possesses some isotactic sequences in random order. Though it is the homopolymer of propylene, it is a characteristic polymer having low melting point, transparency and elasticity. This soft polypropylene does not have the drop in the glass transition temperature, and the drop in the compatibility to polypropylene in comparison with propylene copolymer, which is a kind of the conventional soft polypropylene.

Orientation dynamics of small additive molecules in polymeric films during hot-stretching was investigated by using birefringence analysis and polarized Fourier-transfer infrared (FT-IR) spectroscopy. Birefringence data indicated parallel orientation of the small molecules to main chain of the matrix polymer. Furthermore, polarized FT-IR spectra demonstrated that the ratio of orientation functions of rigid and flexible portions in hexa-methylene naphthalate oligomer showed temperature dependence. The result suggests that the small molecules exhibit two-step orientation in the matrix polymer during stretching.

Biocompatible and biodegradable polymers have emerged during the past decades to promise extraordinary breakthroughs in a wide range of diagnostic and therapeutic medical devices. Understanding and controlling the interfacial interactions of the polymeric biomaterials with biological elements are of essential towards their successful implementation in biomedical applications. Here, we highlight recent developments of biocompatible and biodegradable fusion polymeric biomaterials for medical devices and overview of the recent progress of the design of the multi-functional biomedical polymers by controlling biointerfacial water structure through precision polymer synthesis and supramolecular chemistry.

For the synthesis of a ladder polyamide, 4,6-diaminoisophthalic acid-type monomers were synthesized and their polymerization was studied. Although the polymerization of the A₂- and B₂-type monomers with a base afforded small molecular weight-products, the polymerization of the AB-type monomer gave higher molecular weight-products. Analysis of the products by means of matrix-assisted laser desorption ionization time-of-flight mass spectrometry revealed that they were composed of polymers and oligomers with linear and cyclic structure.

Applications of l-Glu molecularly imprinted cellulose membranes to chiral separation were studied. LiCl, which was adopted to dissolve cellulose into solvent, N,N-dimethylactamide (DMAc), worked well as a print molecule to construct recognition sites toward Li⁺ (or LiCl). The chiral separation ability was greatly dependent on LiCl. The permselectivity was increased with the LiCl concentration and asymptotically reached the maximum value at higher LiCl concentration region. The affinity constants between LiCl and LiCl recognition sites in both control and l-Glu molecularly imprinted membranes were determined to be 65 mol⁻¹ dm³.

Protein nanogels were prepared by using the vitamin B₆ (pyridoxal)-bearing pullulan (PLPP) as a bio-crosslinker. The binding of the PLPP to the serum albumin via the formation of Schiff bases was significantly enhanced in the presence of zinc ions because of the coordination of the Schiff base to metal ions. Dynamic light scattering measurements, high-performance liquid chromatography, and transmission electron microscopy confirmed that the zinc ions enhanced the ability of PLPP to form nanogels by crosslinking with the anionic BSA despite the strong electrostatic repulsion between the two molecules.

Novel organic–inorganic hybrid nanoparticles with a bisphenol A (BPA)-responsive hydrogel layer on the surface of SiO₂ nanoparticles were prepared via surface-initiated atom transfer radical polymerization of acrylamide (AAm), acryloyl-modified β-cyclodextrin (CD) and N, N′-methylenebisacrylamide. The resulting CD-PAAm/SiO₂ nanoparticles shrank in response to BPA because of an increase in the crosslinking density of the CD-PAAm hydrogel layer, which resulted from the formation of sandwich-like CD-BPA-CD complexes acting as dynamic crosslinks.

A ‘box-shaped’ three-dimensional (3D) DNA origami of ~40-nm dimensions was selectively formed by closing a symmetric open motif with three orthogonal faces. This 3D DNA origami was used as an intelligent nano-container to encapsulate exactly one 10-nm gold nanoparticle (AuNP). AuNPs were functionalized with thiol-modified DNA strands and attached to one of the faces of the open motif, which was designed to be an interior surface of the box and decorated with three complementary strands. The open motif was then closed into the box shape as triggered by the addition of DNA strands joining the remaining edges. An examination of the suitable folding path of an M13 scaffold using fluorescently labeled staple strands revealed that the flexibility at the hinge was essential for the efficient closing of the DNA origami container. Atomic force microscope and transmission electron microscope imaging of agarose-gel-purified complexes clearly showed the successful encapsulation of one AuNP inside the shell.

Poly(l-lactic acid-co-glycolic acid)/hydroxyapatite composites were prepared by in situ polymerization of l-lactide and glycolide in porous HAp pellets for their application to the artificial bone materials. Effect of l-lactic acid/glycolic acid ratio on the mechanical properties and biocompatibility were investigated.

Thin-film inorganic/organic hybrids of CaCO₃ and poly(cyclodextrin) were prepared. The cavities of CDs inside the hybrids facilitated functionalization of these fusion materials by dye molecules.

This review addresses recent developments in angle-independent structurally colored materials composed of submicrometer-sized fine particles. Here, especially, I focused on the possibility of using colloidal amorphous arrays as angle-independent structurally colored stimuli-responsive materials based on the properties of colloidal amorphous arrays that have been elucidated in recent experimental investigations.

The effect of the content of carboxy groups in oxidized cellulose nanofiber (CeNF) on hydroxyapatite (HAp) formation capability in biomimetic processing using a solution mimicking human body fluid (simulated body fluid; SBF) was systematically investigated. Oxidized CeNF with different carboxy group contents (0–27% per glucose units of cellulose) were soaked in 1.5SBF, in which concentration was 1.5 times higher than that of SBF. It was found that there was optimum amount of carboxy groups for the effective induction of HAp nucleation on CeNF.

Electropolymerization of pendant groups in a copolymer of TEMPO- and aniline-substituted norbornene gave a layer of TEMPO-populated polynorbornene in which polyaniline chains were incorporated. The polyaniline chain served as a conducting path to reduce charge-transfer resistance for redox mediation, which gave rise to an excellent rate performance for charging/discharging process.

This review focuses on using an organic (bio)polymer for the formation of organic/inorganic hybrid materials and on understanding the formation of new hybrid materials via bio-inspired approaches. The structure–function relationships of biomineralization-related proteins and molecular designs to control the properties of the hybrid materials are also described. The combination of experimentation and molecular simulation is also introduced. These studies provide useful ideas for the development of hybrid materials through biomimetic approaches.

The alternating copolymers containing planar chiral 4,12-disubstituted[2.2]paracyclophane and quaterthiophene units in the main chain were prepared. The obtained optically active polymers exhibited mirror image Cotton effect, and split in the CD sign that was predicted by the exciton chirality method. A mirror-image CPL response in the polymer solution was also observed with a relatively large g_lum value on the order of 10^–4, suggesting that the polymer forms optically active higher-ordered structures such as zigzag and/or helical structures in the excited state.

A polysilsesquioxane-based organic-inorganic hybrid membrane was prepared and applied as a proton-conducting membrane for fuel cells. A membrane of a random copolymer of ethyl 4-(2-methyl-3-triethoxysilylpropoxy)benzenesulfonate and triethoxy(methyl)silane showed proton conductivity of 2.0 × 10⁻⁵ to 1.1 × 10⁻³ S cm⁻¹ at room temperature. A membrane of a block copolymer of poly(3-(4-ethoxysulfonylphenoxy)-2-methylpropyl)silsesquioxane (SPES) and polymethylsilsesquioxane showed proton conductivity of 2.5 × 10⁻³ S cm⁻¹. The mixture of SPES and poly(vinyl alcohol), poly(ethylene oxide), or polyoctahedralpolysilsesquioxane showed proton conductivity of 2.7 × 10⁻³, 1.5x10⁻³ or 2.5 × 10⁻³ S cm⁻¹, respectively. The open-circuit voltage of the SPES membrane was 0.92 V.

HEC (or HMHEC) gel swells due to increasing SDS concentration, while the cooperative diffusion becomes faster. This indicates that the HEC (or HMHEC) gel can swell until the osmotic pressure equals the modulus when the charge effect dominates over the effect of configurational entropy for uncharged gels interacting with charged surfactants.

Dendritic morphologies of a metal oxide, metal and conductive polymer were obtained by using the dendrites of a transition metal salt as a template. Dendrites of the transition metal salt, copper acetate monohydrate (Cu(CH₃COO)₂·H₂O), were prepared under diffusion-controlled conditions in a polymer matrix, such as poly(vinyl alcohol). The resultant dendritic morphologies of Cu(CH₃COO)₂·H₂O were replicated to copper oxide (CuO), metallic copper (Cu) and polypyrrole without morphological changes. These methods can be applied to other metal oxides, metals and polymers.

Amphiphilic block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (EOVE-b-MOVE) induce the ring assembly of silica nanospheres (SNSs, ca. 15 nm) in the liquid phase. Nanorings form with appropriate polymer concentration, pH and temperature. EOVE-b-MOVEs with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that polymer’s molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) one-dimensionally assemble into nanochains with these block copolymers under otherwise identical conditions.

Second- and third-generation hydroxy-terminated polyhedral oligomeric silsesquioxane (POSS)-core dendrons (that is, G2POSS-OH and G3POSS-OH, respectively) and third-generation carboxylic acid-terminated POSS-core dendron (G3POSS-COOH) were prepared. Casting of a methanol solution of G3POSS-OH provided optically transparent films. Methanol solution of G2POSS-OH generated opaque whitish films. Casting of a 2.6 m formic acid solution of G3POSS-COOH resulted in a highly transparent free-standing film. The peripheral functional groups may have been exposed on the surface of the cast films, which enabled control of the wettability of the films via the polarity of the COOH groups.