Polymerization of Fullerene in Solution with Free Electron Laser Irradiation
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Polymerization of Fullerene in Solution with Free Electron Laser Irradiation Nobuyuki Iwata, Yasunori Iio, Shigo Ando, Ryo Nokariya, and Hiroshi Yamamoto Electronics & Computer Science, College of Science & Technology, Nihon University, 7-24-1 Narashinodai, Funabashi-shi, Chiba, 274-8501, Japan ABSTRACT The free electron laser (FEL) of 450 or 500 nm was irradiated onto the pressed C60 powder in vacuum. Blue, purple, yellow, and white grains with µm-order were observed in optical microscope images of the sample surface in parts. The Ag(2) derived mode around 1460 cm-1 in Raman spectra was observed from the grain, indicating the polymerization. The 100 µmlength grain was obtained just after dissolving the FEL irradiated specimens into the toluene and evaporating it. In order to expand the size of C60 polymer grains and to obtain an amorphous C60 polymer, the FEL irradiation was carried out in solution with the reduction of the directivity for polymerization. Although polymerization was not promoted in C60 precipitation in supersaturated solution due to low density of C60, the precipitation grown with the liquid-liquid interfacial precipitation (LLIP) method showed the 1454 cm-1 Ag(2) derived mode in addition to the peaks around 1460 cm-1 in toluene. In m-xylene with LLIP method, in a whole area of C60 pillar-grains, polymerization was confirmed by the Raman analysis. INTRODUCTION Polymerization processes for C60 molecules have been developed for photo-, electronbeam-, pressure-, and plasma-induced methods. Among them, a crystalline three-dimensional (3D) C60 polymer can be obtained at 15 GPa and approximately 650ºC from a two-dimensional (2D) polymer; however, the 2D polymer remains in part and includes a graphite like amorphous phase[1]. The aim of our study is to develop a novel photopolymerization process for C60 molecules and synthesize an amorphous 3D C60 polymer on the bulk scale for various applications. We expect the features of the polymer to be the hardness higher than diamond, the flexibility like organic material owing to the amorphous phase of C60 polymer with 2+2 cycloaddition, and the density lower than that of alloys[2]. We chose a free-electron laser (FEL) as a light source, which has unique features: a tunable wavelength in the infrared range, and a 20 µs macropulse containing several hundred micropulses with a pulse width less than one ps[3]. In the previous reports, the wavelength dependence of polymerization degree was discussed for a pressed C60 powder, in which a 450 and 500 nm wavelength is most efficient for polymerization[4-6]. However, the grain size of C60 polymer prepared by irradiating FEL was limited to µm order. In general the direction of the polymerization by 2+2 cycloaddition reaction is determined. When the structure of the as-pressed C60 powder is the fcc polycrystal, demonstrated by the results of X-ray diffraction, the most likely explanation of the limitation of the polymer size is the directivity of polymerization. Inserting some molecules with double bonds betwee
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