Cyclic imino ethers — Polymerization chemistry and polymer characteristics

This paper describes recent developments in polymerization of cyclic imino ethers, 2-oxazolines and 5,6-dihydro-4H-1,3-oxazines, which have been performed mainly in our laboratory. Cationic ring-opening polymerizations of these two kinds of monomers gave poly(N-acylethylenimine)s and poly(N-acyltrimethylenimine)s, whose hydrolysis produced linear poly-ethylenimine and poly(trimethylenimine), respectively. The mechanism of the polymerization is mainly governed by the nature of monomer and of the counter anion derived from initiator. There are two types of stable propagating species; cyclic onium species and covalent alkyl halide species. In a specific case, e.g., the polymerization of 5-methyl-2-oxazoline with MeI initiator, both ionic and covalent species are involved in equilibrium and propagate concurrently. Then, a new terminology of “Electrophile Polymerization” has been proposed as a broader expression including cationic and covalent propagating species. By utilizing living nature of the cyclic imino ether polymerization, block copolymerizations between these monomers were performed. A poly(cyclic imino ether) chain becomes hydrophilic or lipophilic depending on the monomer. Product AB and ABA type block copolymers were soluble in water and showed excellent surface properties reflected by values of surface tension (γ), when A (or B) and B (or A) are hydrophilic and lipophilic. Thus, various nonionic polymer surfactants of block and graft type have been prepared from cyclic imino ethers. Finally, poly(N-acetylethylenimine) chain showed good compatibility with poly(vinyl chloride). Cellulose diacetate and poly(vinyl chloride) are not miscible, but cellulose diacetate g-poly(N-acetylethylenimine) is miscible with poly(vinyl chloride), the graft chain acting as a “compatibilizer”.     

Swelling behavior of the filling-type membrane

A model that can express the swelling of the filling-type membrane was developed by modifying a model that was developed for a crystalline polymer. The filling-type membrane is composed of two different polymers. One is porous substrate and another is a polymer that filled pores of the substrate. The filling technique can effectively suppress polymer swelling due to the substrate matrix. The model needs two parameters: one is a unit ratio of tie segments in the substrate to the filling polymer, f, which can express a mechanical strength of the substrate, and another is the Flory interaction parameter, χ, between the filling polymer and a solvent that expresses a mixing energy. A porous high-density polyethylene film was used as a porous substrate, and plasma-graft filling polymerization technique could make the filling-type membrane. Methylacrylate was used as a grafting monomer that filled the pores of substrate. A swelling behavior of the filling-type membrane and pure poly(methylacrylate) were measured by the vapor sorption method at different solvent activities. The model was in good agreement with experimental results for the filling-type membrane. Using the model, swelling of the filling-type polymer was compared with a crosslinked polymer, which can be expressed by Flory and Rehner model. The comparison showed that the filling technique is a good way to suppress polymer swelling, and a high crosslinking density is needed to obtain the same level of swelling suppression effect the filling type membrane showed. © 1997 John Wiley & Sons, Inc.     

Atomic structure and stability of elliptical carbon onion

Elliptical carbon onions were produced from amorphous carbon by electron beam irradiation. Atomic structure and structural stability of the onion were investigated by high-resolution electron microscopy, molecular mechanics calculation and molecular orbital calculation, and a structure model of C₂₄@ C₈₄ was proposed at the center of the elliptical onion. Received 30 November 2000     

Approaches to polymer superlattice and molecular device

Approaches to polymer superlattice and molecular devices are shown, demonstrating with functional molecule material by incorporation of a functional molecule into the conducting polymer, conjugating copolymer superlattice by a novel potential programmed electro polymerization, ultrahigh anisotropic conductive LB heterolayers, and porphyrin arrays connected with conducting molecular wire and insulating molecular wire. These results show a practical method to fabricate ultimate functional materials such as molecular device which is the smallest functional material, and quantum functional material which creates a novel nature.     

Controlled radical polymerization of styrene in the presence of nitronyl nitroxides

Bulk radical polymerization of styrene in the presence of nitronyl nitroxides (2-(4-substituted phenyl)-4,4,5,5-tetramethyl-4,5-dihydroimidazolyl-1-oxyl 3-oxide) was studied. All nitronyl nitroxides, like other nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO), act as reversible radical scavengers. The efficiency of controlling the polymerization is affected by the substituent at the 4′-position. The efficiency increases with electron donating strength of 4′-substituents, at least at the beginning of the reaction. However, the thermal stability of nitronyl nitroxides decreases in the same order. Thus, TEMPO is more suitable than nitronyl nitroxides for controlled/“living” radical polymerization of styrene.     

Potassium hydrogen trans‐glutaconate monohydrate at 295, 245 and 40 K,and its rubidium analogue at 298 K

A centrosymmetric and short O—H?O hydrogen bond was found in isomorphic crystals of potassium hydrogen trans‐glutaconate monohydrate (potassium hydrogen trans‐pent‐2‐ene‐1,5‐dioate, K⁺·C₅H₅O₄^?·H₂O), (I), and rubidium hydrogen trans‐glutaconate monohydrate (rubidium hydrogen trans‐pent‐2‐ene‐1,5‐dioate, Rb⁺·C₅H₅O₄^?·H₂O), (II). The O?O distance at room temperature is 2.444 (3) Å in (I), and 2.417 (4) Å in (II). The O?O distance for (I) showed no significant decrease at low temperatures.     

Design and synthesis of a dimeric derivative of RK-682 with increased inhibitory activity against VHR, a dual-specificity ERK phosphatase: implications for the molecular mechanism of the inhibition

BACKGROUND: VHR is a dual-specificity phosphatase, which dephosphorylates activated ERK1/2 and weakens the ERK signaling cascade in mammalian cells. A selective inhibitor is expected to be useful for revealing the physiological function of VHR. RESULTS: First, we investigated the molecular mechanism of VHR inhibition by a known natural product, RK-682. Kinetic analysis indicated that inhibition was competitive toward the substrate, and two molecules of RK-682 were required to inhibit one molecule of VHR. Based on the structure-activity relationships for VHR inhibition by RK-682 derivatives, we constructed a binding model using molecular dynamics calculation. Based on this model, we designed and synthesized a novel dimeric derivative. As expected, the dimeric derivative showed increased inhibition of VHR, supporting our proposed mechanism of VHR inhibition by RK-682. CONCLUSION: We have developed a novel inhibitor of VHR based on the results of kinetic analysis and docking simulation.     

Adsorption of fluoride ions onto carbonaceous materials

The characteristics of fluoride ion adsorption onto carbonaceous materials were derived as adsorption isotherms at different temperatures and in different pH solutions. The fluoride ion was adsorbed into pores in carbonaceous materials produced from wood; the larger the specific surface area, the more fluoride ions adsorbed. Bone char was the most effective adsorbent. The composition of bone char includes calcium phosphate, calcium carbonate, and so on. This suggests that the phosphate ion in bone char was exchanged with a fluoride ion. Moreover, the mechanism of fluoride ion adsorption onto bone char is clearly chemical in nature because the amount of fluoride ion adsorbed onto bone char increased with increasing temperature and decreasing pH. The amount of fluoride ion adsorbed onto bone char was also shown to depend on the concentration of sodium chloride in solution because of the "salting-out" effect. The adsorption of fluoride ion onto bone char is endothermic. Bone char can be utilized to remove fluoride ions from drinking water.     

Over-doping of Tl2Ba2CuO6 due to charge transfer Tl-(Cu-O)

Superconductivity was observed in La substituted Tl₂Ba₂CuO₆. Both T_c and unit cell dimension, a, increase with increasing La concentration, indicating that an over-doping state in Tl₂Ba₂CuO₆, which was due to charge transfer Tl^3−t-(Cu-O)^p as supported from XPS measurements, was relieved by La substitution for Ba.