Manabu Seno

Swelling of poly(methacrylic acid) gels and adsorption of L-lysine and its polymer on the gels

Poly (methacrylic acid) gels (PMAA gels) of various degrees of crosslinking were prepared and the dissociation behavior of these gels was examined; the swelling behavior was investigated as a function of the solution pH values. A reentrant phenomenon of swelling was observed and interpreted based on the Flory-Huggins equation and the Donnan equilibrium formula. Moreover, adsorption of L-lysine, oligo(L-lysine)s (Lys-n,n=3, 9, and 19) and poly(L-lysine) onto PMAA gels from aqueous solutions was investigated under different conditions of pH and concentration of adsorbate. The adsorption ratio of L-lysine onto PMAA gel is dependent on both the pH of solution and the degree of crosslinking. In a pH range between 8 and 9, the protonated form of L-lysine is strongly adsorbed on the PMAA gel by electrostatic interactions. Oligomers and polymer of L-lysine are adsorbed in a somewhat different way from the monomeric L-lysine. In addition, the desorption behavior of L-lysine from PMAA gels by a change in pH was also investigated.

Pervaporation of water-dioxane mixtures with poly(dimethylsiloxane-CO-siloxane) membranes prepared by a sol-gel process

Abstract Poly(dimethylsiloxane- co -siloxane) membranes were prepared from dimethyldiethoxysilane (DMDES) and tetramethoxysilane (TMOS) by a sol-gel process and the structure was characterized by means of high-resolution solid-state 29 Si magic angle spinning NMR spectroscopy. The membranes were used for pervaporation separation of water-dioxane mixtures. Fairly high selectivity was attained; however, it became poorer as the TMOS content increased. The preferential permeation behavior was analyzed on the basis of the Flory-Huggins theory extended to a three-component system, solvent (1)-solvent (2)-polymer (3).

Detailed mechanism and molecular weight dependence of thermal degradation of polyisobutylene

Abstract The products of thermal degradation of polyisobutylene are successfully simulated according to a radical chain reaction model including diffusion-controlled termination reactions of primary and tertiary terminal macroradicals (R p · and R t ·) and volatile small radical (S·). The model proposed consists of the following three steps: (1) end and random initiation reactions, (2) depropagation consisting of depolymerization and intramolecular and intermolecular hydrogen abstractions followed by β scissions, and (3) diffusion-controlled termination consisting of bimolecular reactions between respective macroradicals and vaporization of volatile radicals. The molecular weight ( M ) dependencies of rates of the end initiation and termination are evaluated by M −1 and M − n , respectively. Assuming that the reaction occurs competitively under steady state conditions regarding the respective radicals, their concentrations could be approximately expressed as a function of M . The observed values of the compositions of the studied components of the volatile oligomers and functional groups of the nonvolatile oligomers formed by the degradation at 300°C, are consistently traced by simulation using the above model when the value of n is about 2 for the self-diffusional motion of the reacting radical in the molten polymer matrix. Rates of decreases in concentration are of the order: S· > R p · ⪢ R t ·. This results from an increase in the rate of termination with a decreasing molecular weight of the matrix as the reaction proceeds.

Preparation and characterization of end-reactive oligomers by thermal degradation of polyisobutylene

Abstract The chemical structure of the non-volatile oligomers ( M n = 2600–9000) isolated from the polymer residues obtained by the thermal degradation of polyisobutylene at 300 and 320°C was determined by 400 MHz 1 H n.m.r. spectroscopy with regard to the reactive end groups. The functional groups formed in the degradation process are as follows: tert-butyl end group (t-Bu), isopropyl end group (i-Pr), terminal trisubstituted double bond (TTD), terminal vinylidene double bond (TVD), and non-terminal trisubstituted double bond (NTTD). The average number of TTD and TVD per molecule ( f t ) is in a range from 1.46 to 1.64. This value suggests that 53–67 mol% of the non-volatile oligomers are telechelic oligomers having both TTD and/or TVD, and 39-29 mol% of the oligomers are macromonomer-like oligomers having a double bond at one chain end. Both t-Bu and i-Pr are produced by the intermolecular hydrogen abstraction of primary and tertiary terminal macroradicals, and the subsequent β scission of the resulting on-chain macroradicals at the skeletal CC bond of the main chain yields TTD and TVD. The formation of telechelic oligomer is interpreted by a major contribution of the hydrogen abstraction of volatile radicals, in addition to a minor contribution of the hydrogen abstraction of terminal macroradicals.

Photo-controlled extraction and active transport of amino acids by functional reversed micelles containing spiropyran derivatives

In a reversed micellarn-decane solution, a spiropyran derivative 3′,3′-dimethyl-1′-octadecyl-6-nitrospiro(2H-benzopyran-2,2′-indoline) (PC18) showed normal photochromism, and the reversed micelles provided polar microenvironment increasing stability of a zwitterionic merocyanine (MC) form of PC18. Though the reversed micelles of tetraethyleneglycol dodecylether (TEGDE) alone inn-decane had relatively low ability to extract amino acid from aqueous solutions, the PC18-incorporated TEGDE reversed micelles inn-decane showed good photo-controlled extraction of zwitterionic amino acid under UV-irradiation and release under VIS-irradiation. Extent of the extracted amino acid was higher for tryptophane (Trp) bearing hydrophobic side chain than alanine (Ala), showing amino acid selectivity. Photo-driven active transport of amino acid across a liquid membrane was attained by the PC18-incorporated TEGDE reversed micellar carrier in a water/n-decane/water three-phase system, where one side of an aqueous/organic interface was irradiated by the UV-light and the other side by the VIS-light. When Trp and Ala were present in the aqueous solution, Trp was selectively transported.

Selective Elution of Uranium from Amidoxime Polymer. II

Abstract The separative elution of uranium from an amidoxime polymer was examined by the column method with hydrochloric acid solutions. The amidoxime polymer was immersed in seawater for 40 d for preparation of an uranium-loaded polymer sample for the elution experiments; the metal ions adsorbed were Mg(II), Ca(II), Fe(III), Ni(II), Cu(II), and Zn(II) as well as UO2(VI). It was found from the pH dependence of elution extent by a batch method that the order of elution pH values is Fe(III) < UO2(VI) < Cu(II) < Ni(II) < Zn(II) < Ca(II) < Mg(II). In the elution by a column method, Mg(II), Ca(II), Zn(II), and Ni(II) were eluted completely by 0.1 M HC1 and the eluate of enriched uranium was obtained by a succeeding elution with 0.5 or 1 M HC1. This eluate contained Cu(II). and Fe(III), which could be removed in the succeeding step. The elution treatment with hydrochloric acid solutions hardly affected the adsorptivity for uranium in seawater. It was suggested that the elution of uranium with hydrochloric acid ...

Synthesis of alkyl and arylthioglycosides and thiodisaccharides via thioiminium salts in a two-phase system

Abstract A novel method was developed for the synthesis of alkyl- and arylthioglycosides and thiodisaccharides via glycosylthioiminium salt in a two-phase system using a phase transfer catalyst (PTC). Tetrabutylammonium thiocyanate and tetrabutylphosphonium bromide show a highest efficiency as a PTC for this method. In general, the phosphonium salt is more effective than the ammonium salt as a PTC, and the effect of counter anions of PTC of tetrabutylammonium type is in the order, SCN − >Br − >HSO 4 − >Cl − . The reactivity of alkyl halide RX is in the order RI>RBr>RCl, independently of the kind of PTC. Using this method, various thioglycosides were prepared in fairly good yields higher than 80%. The reactions proceed easily under mild conditions without a sulfur reagent giving an unpleasant smell.

NOVEL SYNTHESIS OF 1-THIOGLYCOPYRANOSES VIA THIOIMINIUM SALTS

Methanolysis of a glycosylthioiminium salt, which was prepared from the reaction of acetohalogenosugar with thioacetamide, afforded the corresponding per-O-acetylated 1,2-trans-1-thioglycose in good yield after fractional crystallization. This synthetic method is very convenient in operation and proceeds without loss of acetyl groups, as the reaction is carried out under mild and neutral conditions.

Gas permeabilities of perfluorocarboxylate membranes in various ionic forms

Gas permeation properties of perfluorocarboxylate membranes in the H+-form and various saltforms have been investigated in the dry state. Gas permeabilities depend on the ion radius of counter cations and the ion-exchange capacity. It was concluded that gas molecules easily pass through the hydrophobic domains formed by perfluorocarbon chains, and that the permeation rate depends on the flexibility of the perfluorocarbon chains and, therefore, on the free volume of the domains. The ion clusters formed by ionic groups of the membrane matrix are considered to be a type of crosslinking, and their size and tightness determine the size of the free volume of the matrix. The experimental results on gas permeabilities were interpreted taken these factors into consideration.

Rhythmic crystallization of ascorbic acid precipitated from its methanol solutions

Abstract As an example of the formation of dissipative structures, appearance of rhythmic crystallization during precipitation of ascorbic acid from its methanol solution is reported. In this system, regular concentric rings of large and small pitches were observed. The branching process by the Mullins-Sekerka instability proceeds autocatalytically, and the hypothesis of a hysteresis relation of the number of branched crystals to the degree of supersaturation is proposed and therefrom the rhythmic crystallization will be explained.