Articles in 2010

The scanning electron microscope images show how the pore diameter is changing as the time of thermal treatment is increasing. In the graphic, one can appreciate the oscillatory behavior of the pore size and the fitting curve obtained when the mathematical model is applied to the experimental data.

This article reviews the development of catalysts for ring-opening metathesis polymerization (ROMP), synthesis of polymers bearing amino acids and peptides by ROMP of functionalized norbornenes, formation of aggregates and micelles, and applications of the polymers to medical materials. It also describes the control of monomer unit sequences, that is, living polymerization to synthesize block copolymers, and alternating copolymerization that is achieved on the basis of acid–base interactions.

Hyperbranched polysiloxanes were synthesized by polyhydrosilylation of silsesquioxane derivatives and vinyl derivatives in the presence of Karstedt's catalyst. The obtained hyperbranched polymers were soluble in common solvents and exhibit good thermal stability. The refractive index values of the obtained polymers tend to decrease with increasing structure size of co-monomers.

The synthesis and photo-polymerization of hyperbranched polyesters containing pendant methacryloyl groups (HBPE-MA) were examined. Polycondensations of 1,4-bis(chloromethyl)benzene (BCMB) with 1,3,5-benzenetricarboxylic acid (BTCA) proceeded very smoothly to give the soluble hyperbranched polyesters (HBPE) in satisfactory high yields using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Furthermore, HBPE-MA was synthesized by the reaction of HBPE with methacrylic acid (MAA) by the DBU method. The photo-induced radical polymerization of HBPE-MA was performed in the presence of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-2-one (Irgacure 907) as a photoinitiator in the film state upon UV irradiation to afford the insoluble cured film.

Polypropylene (PP)-knitted fabrics were finished with β-cyclodextrin (β-CD) through their crosslinking with citric acid (CTR). The polyCTR–β-CD polymer-coated fibers were wash resistant. We report that the rate of immobilized CD was controlled by temperature and curing time. The weight increase of the fabrics on their modification with native β-CD and CTR could reach 30 %wt. The treated PP supports were dyed by applying classical dyeing processes involving disperse, acid and reactive dyes. Standard tests of wash fastness (shade change and staining) were conducted and showed that all dyes were fixed, because of inclusion complexation with the immobilized cavities on one hand and sorbed hydrogen or ionic bonds that also occurred between the polyCTR–β-CD coating and the tested dyestuffs on the other.

Isotactic (it-) and syndiotactic (st-) uniform poly(methyl methacrylate)s (PMMAs) with hydroxyl end group, isolated by supercritical fluid chromatography (SFC), were reacted with benzene-1,3,5-tricarbonyl trichloride, and two types of uniform three-arm star-PMMAs with different stereoregular arms, [it/it/st]- and [it/st/st]-3-star-PMMAs, were isolated by SFC from the product mixture. The stereocomplex formation of these stereostar PMMAs was examined in acetone. Although both stereostar PMMAs formed intramolecular stereocomplexes, the [it/st/st]-3-star-PMMA, in particular, was found to form two types of intramolecular stereocomplexes with different hydrodynamic volumes because of different compositions of it- and st-PMMA arms involved in the stereocomplexes.

Hyperbranched polycarbonates (HBPCs) were synthesized by A₂+B₃ polymerization, particularly using di-tert-butyl tricarbonate (DBTC) as A₂ monomer and 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) as B₃ monomer. The terminal functionalized HBPCs with Boc and phenol were obtained by using 1-pot or 2-pot synthesis.

Arm-replaceable star-like nanogels consisting of poly(methyl methacrylate) arms and poly(divinylbenzene) cores with alkoxyamine units at their branching points were synthesized by a combination of atom transfer radical polymerization and nitroxide-mediated radical polymerization. The arms of the star-like nanogels were replaced by means of dynamic covalent exchange processes, and arm detachment and arm exchange reactions were successfully accomplished. The structural changes were confirmed by gel permeation chromatography–multiangle light scattering measurements, small-angle X-ray scattering measurements and scanning force microscopic observation.

Distinct skin-core structured PET X(a) proved notch sensitive as shown in Y(a) when 5–60 μm-deep hairline cracks were introduced. PET was annealed in hot edible oil to alter its morphology and remove internal stresses [PET X(b)] in order to improve toughness. Results showed significant reduction in its notch sensitivity, as shown in Y(b). Therefore, annealing in hot oil proved to be effective in achieving more dispersed skin-core morphology, thus improving the toughness of PET.

Hyperbranched poly(ether sulfone)s (HBPES) possessing sulfonic acid at the terminal point were prepared by the electrophilic reaction of sulfonium ions to electron-rich benzene rings starting two kinds of AB₂ monomers. First, linear and hyperbranched multiblock copolymers were successfully prepared by the reaction of oligomeric linear PES and AB₂ monomer. Next, from these multiblock copolymers, a linear and hyperbranched PES blend was prepared and applied as ion-exchange membranes for fuel cells. The blend films showed comparable ion-exchange capacity with Nafion 117 membrane.

Poly(arylene sulfone)s (PASs) containing 9,9′-spirobifluorene (SBF) skeleton in the main chain were synthesized in high yields by the oxidations of the corresponding poly(arylene thioether)s. The PASs exhibited good thermal stability (T_g 257–370 °C, T_d5>400 °C under nitrogen), and showed high solubility in ordinary organic solvents, such as CHCl₃, N-methylpyrrolidone (NMP) and N,N-dimethyl formamide (DMF). All films of PASs showed higher refractive indices in the range 1.65–1.67 at 587.6 nm than those of commercially available polysulfone, whereas it hardly showed birefringence. These excellent optical and thermal properties are derived from the C₂ symmetry and high aromatic component of SBF moiety. Polymer: (i) High refractive index, (ii) Low birefringence, (iii) High thermal stability, (iv) High transparency, (v) High solubility and (vi) Less coloration.

Hydroxyl-group-alkoxylated lignophenols (LPs) with various types of alkyl halides were prepared by Williamson ether synthesis to reutilize lignin, an industrial waste material, and make it processable. As compared with raw LP, alkoxylated LPs exhibited good organosolubility and thermal stability (temperatures at 5% loss in weight were estimated to be more than 330 °C by thermogravimetric analyses). Alkoxylated LPs could also form transparent thin films; in particular, films of hexyloxyl LPs exhibited high refractive indices (≈1.55) similar to that of bisphenol A-based poly(carbonate) (PC). Furthermore, these films had lower birefringence (<0.001) than that of PC; therefore, alkoxylated LPs can be utilized as natural-polymer-based optical materials.

Permeation of model drugs with different molecular weights through a bioconjugated membrane having antigen–antibody complexes as reversible crosslinks was investigated in the absence and presence of a target antigen. The bioconjugated membrane regulated the drug permeation in response to the concentration of a target antigen. This paper focuses on the effect of the molecular size of the drugs on controlled permeability of the antigen-responsive membrane.

For the purpose of an electric paper application, alginate hydrogel particles were prepared. To increase their zeta potential for well response by electric fields, their surface were modified chemically. Electro-response behaviors were observed between comb-shaped electrodes. It was found that surface-modified alginate hydrogel particles were well responded by applied low voltage 4–9 V.

X-ray scattering from an organogel made from discotic triazine triamide was measured at SPring-8 at a quite wide q range of 0.050 nm⁻¹ <q <20 nm⁻¹. Analyses revealed (1) an amorphous nature of the molecular stacking at a distance of 0.32 nm, (2) the presence of a semiflexible rod-like scattering object with a radius of 1.3 nm and a Kuhn length of 55 nm and (3) branching of the cylinder formed at the gel state.

To obtain a novel biomimetic polymer, we have been studying polymers with an autonomous self-oscillating function. We succeeded in developing a novel self-oscillating polymer and gel by using an oscillating reaction, called the Belousov–Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer is composed of a poly(N-isopropylacrylamide) network in which the catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous cyclic soluble–insoluble changes or swelling–deswelling changes (in the case of gel) without any on–off switching of external stimuli. Several kinds of functional material systems using the self-oscillating polymer and gel, such as biomimetic actuators, mass transport surface and so on, are expected.

The reaction in the presence of poly(γ-glutamic acid) (γPGA) proceeded faster than that without γPGA and the larger molecular weight γPGA was slightly more efficient to catalyze the reaction.

The molecular chaperone function of polysaccharide nanogel was demonstrated for the folding of newly synthesized green fluorescent protein (GFP) in a cell-free protein synthesis system. Nanogel comprising cholesteryl group-bearing pullulan (CHP) trapped unfolded or partially folded GFP expressed in the cell-free system. The structure of the CHP nanogel was disrupted by the addition of cyclodextrins, and the protein complexed with the nanogel was released and folded into the mature form.