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Journal Articles

Flow filtration/adsorption and simultaneous monitoring technologies of radiocesium $$^{137}$$Cs in river water

Enomoto, Kazuyuki*; Hoshina, Hiroyuki*; Kasai, Noboru*; Kurita, Keisuke; Ueki, Yuji*; Nagao, Yuto*; Yin, Y.-G.*; Suzui, Nobuo*; Kawachi, Naoki*; Seko, Noriaki*

Chemical Engineering Journal, 460, p.141696_1 - 141696_9, 2023/03

 Times Cited Count:1 Percentile:53.63(Engineering, Environmental)

This study develops a method that combines a radiation-grafting fibrous Cs-adsorbent filter of ammonium molybdophosphate (AMP) and a Ce:Gd$$_3$$Al$$_2$$Ga$$_3$$O$$_{12}$$ scintillator based $$gamma$$-ray detector for in situ measurements of the activity concentrations of $$^{137}$$Cs in a continuous water flow.

Journal Articles

Temporal variability of $$^{137}$$Cs concentrations in coastal sediments off Fukushima

Suzuki, Shotaro*; Amano, Yosuke*; Enomoto, Masahiro*; Matsumoto, Akira*; Morioka, Yoshiaki*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Kaeriyama, Hideki*; Miura, Hikaru*; Tsumune, Daisuke*; et al.

Science of the Total Environment, 831, p.154670_1 - 154670_15, 2022/07

 Times Cited Count:2 Percentile:32.35(Environmental Sciences)

Journal Articles

Polymerization mechanism for radiation-induced grafting of styrene into Alicyclic polyimide films for preparation of polymer electrolyte membranes

Park, J.; Enomoto, Kazuyuki; Yamashita, Takashi*; Takagi, Yasuyuki*; Todaka, Katsunori*; Maekawa, Yasunari

Journal of Membrane Science, 438, p.1 - 7, 2013/07

 Times Cited Count:14 Percentile:43.43(Engineering, Chemical)

Alicyclic polyimides (APIs) were successfully applied to radiation-induced graft polymerization for developing polymer electrolyte membranes for fuel cells. The grafting into fully aromatized polyimide barely proceeded (grafting degrees (GDs) of less than 5%), whereas that of styrene into the API films proceeded with styrene GDs of up to 70%. In combination of electron spin resonance measurements and ultraviolet-visible (UV-VIS) spectroscopy, the radical species was identified as a long-lived intermediate and 10% of the radicals were consumed as grafting initiators. The moderate reaction conditions allowed for selective sulfonation on the polystyrene grafts, and not on the API substrates, to give API-based polymer electrolyte membranes (PEMs) with ion exchange capacities (IEC) of 1.7-2.8 mmol/g. The PEMs exhibited appropriate proton conductivity and low water uptake, together with excellent mechanical properties, compared with conventional PEMs such as Nafion.

Journal Articles

Synthesis of copolymer grafts containing sulfoalkyl and hydrophilic groups in polymer electrolyte membranes

Enomoto, Kazuyuki; Takahashi, Shuichi; Rohani, R.; Maekawa, Yasunari

Journal of Membrane Science, 415-416, p.36 - 41, 2012/10

 Times Cited Count:15 Percentile:46.26(Engineering, Chemical)

Polymer electrolyte membranes (PEM) consisting of ion conducting alkylsulfonic acid and hydroxyl groups were successfully synthesized by radiation-induced graft polymerization of vinyl acetate (VAc) into a poly(ethylene-$$co$$-tetrafluoroethylene) (ETFE) film, followed by alkylsulfonation with 1,3-propanesulfone. The prepared PEM showed higher conductivity under 30% relative humidity at 80$$^{circ}$$C than that of the conventional poly(styrenesulfonic acid)-grafted ETFE. Furthermore, the prepared PEM also showed better mechanical properties than those of Nafion. Thus, the PEM with hydroxyl groups possesses sufficient mechanical and electrochemical properties, required for a fuel cell, operating at a high temperature and low humidity.

Journal Articles

A Novel characterization method for graft-polymer structures chemically attached on thermally stable polymer films

Enomoto, Kazuyuki; Takahashi, Shuichi; Maekawa, Yasunari

Macromolecular Chemistry and Physics, 213(1), p.72 - 78, 2012/01

 Times Cited Count:10 Percentile:33.23(Polymer Science)

Most polymer grafts in grafted polymer films obtained by radiation-induced solid graft polymerization have not been analyzed in detail due to difficulties in isolation of the grafts without structural decomposition. We report herein a novel structural and molecular weight characterization method for polymer grafts chemically attached to thermally and chemically stable polymer substrates, based on swelling-induced graft detachment in hot water. The polymer grafts prepared by radiation-induced polymerization of alkyl acrylate into poly(ethylene-co-tetrafluoroethylene) (ETFE) followed by a sulfonation reaction were found to have a ternary copolymer structure whose monomer units contained -COOH, -SO$$_{3}$$H, or both.

Journal Articles

Degradation manner of polymer grafts chemically attached on thermally stable polymer films; Swelling-induced detachment of hydrophilic grafts from hydrophobic polymer substrates in aqueous media

Enomoto, Kazuyuki*; Takahashi, Shuichi*; Iwase, Takanori*; Yamashita, Takashi*; Maekawa, Yasunari

Journal of Materials Chemistry, 21(25), p.9343 - 9349, 2011/07

 Times Cited Count:37 Percentile:71.74(Chemistry, Physical)

The degradation manner of graft-type polymer electrolyte membranes consisting of hydrophilic poly(styrenesulfonic acid) (PSSA) graft polymers (grafts) and thermally and mechanically stable hydrophobic polymer substrates was examined in hot water. Severe weight loss was observed in PSSA-grafted cPTFE and ETFE films but not in a PSSA-grafted PEEK film. The decomposed extracts in water were characterized as PSSA during the whole course of degradation, clearly showing that the PSSA grafts detached from the fluorinated substrates without decomposition or scission of graft polymer chains. This is quite a new degradation manner for graft-type polymer electrolyte membranes; namely, hydrophilic PSSA grafts detach from hydrophobic polymer substrates due to swelling-induced stress at the interfacial boundary in the grafted films.

Journal Articles

Electron-beam-induced chromism combined with photo- or thermal reverse reaction for color imaging

Enomoto, Kazuyuki; Maekawa, Yasunari; Kono, Sachiko*; Iwasaki, Masakazu*; Narita, Tadashi*

Journal of Photopolymer Science and Technology, 23(2), p.217 - 224, 2010/06

 Times Cited Count:0 Percentile:0.01(Polymer Science)

Reversible color imaging on polymer films with spiropyran (SP-NO$$_{2}$$) or diarylethene (DE) has been examined by electron-beam (EB) induced chromism combined with a photo- or thermal reverse reaction. Colorless SP-NO$$_{2}$$ in a film transformed into red-colored merocyanine (MC-NO$$_{2}$$), which subsequently converted to the original SP-NO$$_{2}$$ via thermal treatment. In contrast, a photo reverse reaction could be applied for EB-induced color imaging using DE in the polymer films, where the thermally stable colored close-form can be converted to the original colorless open-form via photoreaction. The color images of 200 nm L/S patterns were produced in the PMMA film containing SP-NO$$_{2}$$; the images could be faded upon the thermal treatment. It is noted that these reactions are the first example for reversible transformation of color imaging induced by EB radiation together with heat or light treatment.

Journal Articles

Poly(vinylidene fluoride)-based ion track membranes with different pore diameters and shapes; SEM observations and conductometric analysis

Nuryanthi, N.*; Yamaki, Tetsuya; Koshikawa, Hiroshi; Asano, Masaharu; Enomoto, Kazuyuki; Sawada, Shinichi; Maekawa, Yasunari; Voss, K.-O.*; Trautmann, C.*; Neumann, R.*

Denki Kagaku Oyobi Kogyo Butsuri Kagaku, 78(2), p.146 - 149, 2010/02

 Times Cited Count:6 Percentile:13.75(Electrochemistry)

Poly(vinylidene fluoride) (PVDF) membranes with conical and cylindrical nanopores were prepared in a controlled manner by the ion-track technique, which involved heavy ion beam irradiation and the subsequent alkaline etching. Etching behavior mainly depended on energy deposition of ion beams, and thus its depth distribution, estimated by theoretical simulation, was successfully applied to control the shapes and diameters of the etched pores. Scanning electron microscopy (SEM) and electrolytic conductometry then gave an insight into critical experimental parameters. Interestingly, applying a higher voltage to the conductometry cell promoted track etching up to breakthrough probably because electrophoretic migration of dissolved products occurred out of each pore.

Journal Articles

Long-lived intermediates in radiation-induced reactions of alicyclic polyimides films

Park, J.*; Enomoto, Kazuyuki; Yamashita, Takashi*; Takagi, Yasuyuki*; Todaka, Katsunori*; Maekawa, Yasunari

Journal of Photopolymer Science and Technology, 22(3), p.285 - 287, 2009/08

 Times Cited Count:0 Percentile:0.01(Polymer Science)

Alicyclic Polyimide (A-PI) films were utilized as a substrate of radiation-induced polymerization to prepare PEM for fuel cells. We successfully prepared the A-PI- PEM by radiation-induced grafting of styrene into A-PI films and subsequent sulfonation. The obtained A-PI-PEM has higher ion conductivity and mechanical and thermal properties, compared with conventional PEM (Nafion). Furthermore, the long-lived intermediates in irradiated A-PI films were observed in the UV-VIS spectra. In comparison with the decay profile of ESR spectra of irradiated A-PI films, the initiation radicals (600, 420 nm) and radical anion (720 nm) can be characterized in terms of the graft polymerization mechanism of A-PI films.

Journal Articles

Electron-beam-induced color imaging of acid-chromic polymer films

Maekawa, Yasunari; Yuasa, Kanako*; Enomoto, Kazuyuki; Matsushita, Harumi*; Kato, Jun*; Yamashita, Takashi*; Ito, Kazuo*; Yoshida, Masaru

Chemistry of Materials, 20(16), p.5320 - 5324, 2008/08

 Times Cited Count:2 Percentile:9.32(Chemistry, Physical)

Polymer films with acid-responsive chromic dyes and acid generators have been designed for an electron beam (EB)-induced color imaging system. Arylsulfonic acid esters and triphenylsulfonium salts were used as an EB-sensitive acid generator; the acid (H$$^{+}$$) allows a chromic reaction with rhodamine B base (RB) and 4,4'-bis(dimethylamino)benzhydrol (BH) to be triggered. Upon EB irradiation, poly(methyl methacrylate) (PMMA) films consisting of RB or BH and acid generators exhibited a characteristic absorption band with $$lambda$$max at 560 and at 612 nm, respectively, and an isosbestic point. These spectral changes clearly indicate that colorless chromic dyes in PMMA are transformed selectively to the colored form. The color imaging of these films was performed by electron beam direct writing (EBDW) with a 50 nm diameter beam to form 100 - 1000 nm line and space patterns and was evaluated by optical and confocal laser microscopy. EBDW on the acid chromic polymer films, especially for BH, yielded clear color imaging of 100 - 200 nm line and space patterns with a dose of only 10 $$mu$$C/cm$$^{2}$$. The confocal laser microscopy gave thinner lines than the laser wavelength (632.8 nm), probably because of the large change in refractive index of the patterned film induced by EB irradiation even with a low energy dose.

Journal Articles

Radiation-induced reaction of sulfonamide-containing polymers in the film state for color imaging

Maekawa, Yasunari; Kato, Jun*; Katakai, Masashi*; Ishihara, Masaaki*; Enomoto, Kazuyuki; Hagiwara, Tokio*; Ishii, Tatsuhito*; Ito, Kazuo*; Koshikawa, Hiroshi; Yoshida, Masaru

Macromolecular Chemistry and Physics, 209(6), p.625 - 633, 2008/03

 Times Cited Count:2 Percentile:7.34(Polymer Science)

A polysulfonamide and copolymers consisting of sulfonamides and amides underwent Fries rearrangement and scission, forming amino groups upon EB irradiation. The EB irradiation of these films with a dose of 500 $$mu$$C/cm$$^{-2}$$ followed by the color forming reaction provided the color imaging of line/space patterns with resolution of 300 nm.

Journal Articles

$$gamma$$-rays radiation-induced homopolymerization of trifluorovinyl heptafluoropropyl ether

Narita, Tadashi*; Enomoto, Kazuyuki*; Maekawa, Yasunari; Yoshida, Masaru; Ichikawa, Mitsuru*; Hamana, Hiroshi*

Journal of Fluorine Chemistry, 128(1), p.52 - 54, 2007/01

 Times Cited Count:5 Percentile:19.96(Chemistry, Inorganic & Nuclear)

Perfluorinated polymers have expected to be the key materials for fuel cell membranes owing to the high chemical stability, thermo-durability and optical property. However, a homopolymer of FVPE has never yielded under usual polymerization conditions and alternating copolymers with several non-fluorinated vinyl monomers have only been reported. Thus, using radiation-induced polymerization, in which initiating species (radicals) can be continuously produced, the polymerization of trifluorovinyl heptafluoropropyl ether (FVPE) was examined to afford high molecular weight polymers of FVPE. The formation of FVPE homopolymers was confirmed by NMR and IR spectroscopy.

Journal Articles

Novel electron-beam-induced reaction of a sulfonium salt in the solid state

Enomoto, Kazuyuki*; Moon, S.*; Maekawa, Yasunari; Shimoyama, Junji*; Goto, Kazuyuki*; Narita, Tadashi*; Yoshida, Masaru

Journal of Vacuum Science and Technology B, 24(5), p.2337 - 2349, 2006/09

 Times Cited Count:5 Percentile:33.6(Engineering, Electrical & Electronic)

The electron beam (EB)-induced reaction of triphenylsulfonium methanesulfonate (1-Ms) in the solid state afforded the benzene-substituted product, biphenyldiphenylsulfonium methanesulfonate (2-Ms), which has not been observed by either photolysis or EB-induced reaction in a solution. The kinetic data revealed that the biphenyl salt 2-Ms exhibited 3.7 times greater kinetic constants for consumption than that of 1-Ms. The EB-induced reaction of benzene-substituted triphenylsulfonium salts, p-biphenyldiphenylsulfonium methanesulfonate (2p-Ms) and (4-phenylthiophenyl)diphenyl- sulfonium methanesulfonate (7) showed the consumption rates of 3.8 and 5.7 times greater than that of 1-Ms. The sulfonium salts with aromatic counter anions showed somewhat higher reactivity than those with aliphatic counter anions. Accordingly, it is concluded that the triphenylsulfonium salts having aryl groups, which exhibit lower ionization potential (Ip), in both cation and anion moieties should exhibit greater decomposition rates.

Journal Articles

Refractive index change and color imaging of acid-chromic polymer films using EB-induced acid generation

Kato, Jun; Yuasa, Kanako; Matsushita, Harumi*; Maekawa, Yasunari; Enomoto, Kazuyuki; Ishii, Tatsuhito*; Ito, Kazuo*; Yamashita, Takashi*

Journal of Photopolymer Science and Technology, 19(1), p.105 - 110, 2006/00

 Times Cited Count:2 Percentile:6.52(Polymer Science)

The novel electron beam (EB)-induced color imaging system, consisting of polymer films with acid-responsive chromic molecules (chromic dyes) and EB-acid generators (EBAGs) was proposed. EB irradiation of the acid-chromic polymer films induced acid generation from EBAG, resulting in color formation of the acid-chromic molecules (protonated forms). Nanoscale color imaging on the acid- chromic polymer films was carried out using EB scanning direct drawing. Clear color imaging of 200 nm square and 100 nm line/space patterns could be observed with a dose of only 50 $$mu$$C cm$$^{-2}$$. Furthermore, the large EB-induced refractive index change of these films (0.013 at 632.8 nm) was observed in both TE and TM modes by an m-line method, which is sufficient to create an optical circuit.

Journal Articles

Radiation-induced radical polyaddition of Bis($$alpha$$-trifluoromethyl-$$beta$$, $$beta$$-difluorovinyl) terephthalate with excess of various ethers

Enomoto, Kazuyuki*; Maekawa, Yasunari; Katsumura, Yosuke*; Miyazaki, Toyoaki*; Yoshida, Masaru; Hamana, Hiroshi*; Narita, Tadashi*

Macromolecules, 38(23), p.9584 - 9593, 2005/11

 Times Cited Count:9 Percentile:30.8(Polymer Science)

Radiation-induced radical polyaddition of bis($$alpha$$-trifluoromethyl-$$beta$$,$$beta$$-difluorovinyl) terephthalate [CF$$_{2}$$=C(CF3)OCOC$$_{6}$$H$$_{4}$$COOC(CF$$_{3}$$)=CF$$_{2}$$] (BFP) in the presence of an excess of cyclic and acyclic ethers in feed was examined at 0$$^{circ}$$C using $$gamma$$-rays irradiation. Irradiation of BFP with an 8-fold excess of 1,4-dioxane (DOX) and diethyl ether (EE) gave monomodal polymers consisting of the $$alt$$ ernating unit of BFP and DOX moieties (poly(BFP-$$alt$$-DOX), $$overline{M}$$$$_{n, as-prepared}$$ = 5.1$$times$$10$$^{3}$$) and of BFP and EE (poly(BFP-$$alt$$-EE), $$overline{M}$$$$_{n, as-prepared}$$ =3.9$$times$$10$$^{3}$$), respectively. The irradiation of BFP with an 8-fold excess of tetrahydrofuran or tetrahydropyran provided only 1:2 addition products in high yields. Mono-functional 2-benzoxypentafluoropropene [CF$$_{2}$$=C(CF$$_{3}$$)OCOC$$_{6}$$H$$_{5}$$] (BPFP) as a model compound showed preferential formation of the 2:1 adduct to the 1:1 adduct with DOX and EE. The kinetic analysis of the model reactions revealed that the rate constants for the formation of the 2:1 adducts ($$k_{rm d}$$) of BPFP with DOX and EE were two orders of magnitude higher than those of the 1:1 adducts ($$k_{rm m}$$). Poly(BFP-$$alt$$-DOX) showed higher radiation resistance than poly(BFP-$$alt$$-EE) in solid states as well as in solution. It was concluded that radiation-induced step-growth polymerization under the stoichiometric imbalance of the two compounds requires a high $$k_{rm d}$$/$$k_{rm m}$$ value as well as high radiation resistance for the formation of high molecular weight polymers.

Journal Articles

On the radiation-induced polyaddition of bisperfluoroisopropenyl terephthalate with 1,4-dioxane

Enomoto, Kazuyuki*; Narita, Tadashi*; Maekawa, Yasunari; Yoshida, Masaru; Hamana, Hiroshi*

Journal of Fluorine Chemistry, 125(7), p.1153 - 1158, 2004/07

 Times Cited Count:3 Percentile:11.01(Chemistry, Inorganic & Nuclear)

Radical polyaddition of bis($$alpha$$-trifluoromethyl-$$beta$$,$$beta$$-difluorovinyl) terephthalate (BFP) with 1,4-dioxane (DOX) afforded higher molecular weight polymers under $$gamma$$-rays compared to those yielded by benzoyl peroxide initiation. More detailed study on the radiation-induced polyaddition of BFP with DOX and optimization of the reaction conditions were carried out. It was necessary to irradiate with doses of 2000, 1500, and 750 kGy, to obtain quantitative conversion of BFP at the feed molar ratio DOX/BFP of 8.0, 16, and 32, respectively. Step-growth polymerization mechanism was suggested by the measurements of molecular weights of the polymers obtained with several irradiation doses. It was concluded that the molecular weight of the polymer could be controlled by the feed molar ratio of DOX/BFP and irradiation doses. The reaction between polymers might take place after the quantitative conversion of BFP. Radiation-induced radical polyaddition mechanism of BFP with DOX was proposed.

Journal Articles

Electron-beam-induced fries rearrangement and oxidation reactions of sulfonic acid esters in crystalline state

Yuasa, Kanako; Enomoto, Kazuyuki*; Maekawa, Yasunari; Kato, Jun*; Yamashita, Takashi*; Yoshida, Masaru

Journal of Photopolymer Science and Technology, 17(1), p.21 - 28, 2004/07

 Times Cited Count:9 Percentile:31.15(Polymer Science)

The electron beam (EB)-induced reactions of arylsulfonic acid esters, phenyl p-toluenesulfonate (1a), phenyl benzenesulfonate (1b), and phenyl 1-naphthalenesulfonate (1c), were examined in the balk state. The EB irradiation of 1a afforded the Fries rearrangement products, o- and p-hydroxyphenyl p-tolylsulfones (2a and 3a), phenol (5), and the oxidation product of 2a, o,p-dihydroxyphenyl p-tolylsulfone (4a), which has not been observed in photolysis. The irradiation of 1b, which is liquid at room temperature, gave Fries products, 5, and the oxidation product, o,p-dihydroxyphenyl phenylsulfone. On the other hand, the EB-induced reaction of 1c proceeded with the lowest reactivity through crystal to crystal transformation to afford Fries products and 5, but not oxidation product. The mechanistic study reveals that oxidation product 4a generated by the oxidation reaction of ortho-Fries product 2a but not para-isomer 3a with an active oxidant, which should result from the decomposition of 1a.

Journal Articles

Electron-beam induced reactions of sulfonium salts in a crystalline state

Enomoto, Kazuyuki*; Maekawa, Yasunari; Moon, S.; Shimoyama, Junji*; Goto, Kazuyuki*; Narita, Tadashi*; Yoshida, Masaru

Journal of Photopolymer Science and Technology, 17(1), p.41 - 44, 2004/06

 Times Cited Count:2 Percentile:9.04(Polymer Science)

The Electron beams (EB)-induced reactions of triphenylsulfonium methanesulfonate (1) in the crystalline state gave benzene-substituted product, biphenylsulfonium methanesulfonate (2), which has not been observed by either photolysis. In this paper, the EB-induced reactions of triphenylsulfonium salt derivatives, which possesses aromatic/aliphatic counter anions, have been examined. The anionic moiety of sulfonium salts has practically little effect on the formation of biphenyl salt 2 as well as the other products. The consumption rates of the sulfonium salts containing aromatic counter anions are somewhat smaller in a crystalline state and about two times larger than those of the salts with aliphatic counter anions. The greater decomposition rates of the sulfonium salts with aromatic counter anions than those of aliphatic counter anions in an amorphous state are elucidated by lower ionization potential of the salts with aromatic counter anions such as tosyl and naphthyl groups than those with aliphatic counter anions.

Oral presentation

Electron beam-induced color imaging of acid-chromic polymer films

Enomoto, Kazuyuki; Yuasa, Kanako*; Kato, Jun*; Matsushita, Harumi*; Yamashita, Takashi*; Ito, Kazuo*; Yoshida, Masaru; Maekawa, Yasunari

no journal, , 

The polymer films with acid-responsive chromic molecules Rhodamine B base and 4,4'-bis(dimethylamino)benzhydrol as an acid-chromic compound with electron beam-acid generators were well designed for the novel electron beam-induced color imaging system. Electron beam scanning direct drawing of the acid-chromic polymer films gave clear color imaging of 100-200 nm line/space patterns with a dose of only 10 $$mu$$C cm$$^{-2}$$.

Oral presentation

Electron beam-induced reaction of polymer films containing chromic dye molecules

Enomoto, Kazuyuki; Yuasa, Kanako*; Kato, Jun*; Matsushita, Harumi*; Yamashita, Takashi*; Ito, Kazuo*; Yoshida, Masaru; Maekawa, Yasunari

no journal, , 

A color forming performance for fabricating nanoscale patterned polymer films has been examined using electron beam direct writing (EBDW) techniques. Upon EB irradiation the poly(methyl methacrylate) film consisting of 3 wt% bis(dimethylamino)benzhydrol and the equimolar sulfonium salt has an absorption band at 560 nm, which is assigned to protonated benzhydrol. The appearance of the new band at 560 nm with an isosbestic point in the spectral changes of indicates the quantitative transformation from colorless benzhydrol to the protonated form. The film is then exposed with a raster scanning by EBDW. Upon EB irradiation they also undergo chemical changes to provide optical differentiation between the exposed and unexposed regions. The blue-colored line/space patterns of 100 - 200 nm with a dose of 10 $$mu$$C/cm$$^{2}$$ are achieved.

37 (Records 1-20 displayed on this page)