| Co-Investigator(Kenkyū-buntansha) |
TAKEDA Sadamu Faculty of Science, Osaka University; Research Associate, 理学部, 助手 (00155011)
EGUCHI Taro College of General Education, Osaka University; Associate Professor, 教養部, 助教授 (50107083)
NAKAMURA Nobuo Faculty of Science, Osaka University; Associate Professor, 理学部, 助教授 (70028166)
KATSUBE Yukiteru Institute for Protein Research, Osaka University; Professor, 蛋白質研究所, 教授 (20032013)
MURATA Ichiro Faculty of Science, Osaka University; Professor, 理学部, 教授 (90028077)
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| Research Abstract |
The main interest of the present work has been to look for the possibility of and to clarify the mechanism(s) of the chain-folding in superlong-chain n-alkanes which has been a very important basic problem for the studies of the structure and properties of polymers and biological materials. Our objects were n-C_<50>H_<102>, polyethylenes with the average molecular weights of 595, 1214, and 2305, and poly(ethylene glycols) with the average molecular weights of 2064 and 3662. We applied to these materials the differential scan-ning calorimetry (DSC) to characterize their thermal properties, the ^<13>C cross-polarization/magic angle spinning (CP/MAS) NMR to examine the local chain structure and the possibility of the existence of any chain-folding crystalline parts, and then measured the ^1H spin-lattice relaxation times in the laboratory frame, T_1, and in the dipolar field, T_<1D> to investigate the dynamic structure of long-chain molecules in the cry stals.
To conduct the ^<13>C CP/MAS
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NMR and the relaxation experiments we constructed a pulsed NMR system using an Oxford superconducting magnet with the magnetic field strength of 4.7T; the radio-frequency units for proton and carbon resonances at 200. 1 and 50.3 MHz, respectively, were constructed and combined with a CP/MAS probe provided by Doty Scien-tific, Inc., or with a newly designed probe for the relaxation measurements.
The analyses of the experimental results led to the following results: Partial chian-folding can occur in the n-alkane specimens with the molecular weights 1214 and 3662 which were slowly crystallized from the melt. Samples quenched from the melts do not give folded crystal. These results are inconsistent with a previous demands by Bristol group that chain-folding is possible for the n-alkanes with the carbon number larger than about 150. In the case of poly(ethylene glycol) samples DSC experiments suggest the possibility of existence of partial folding, but no information about the folding was obtained from the ^<13>C CP/MAS spectra because any possible peaks due to the folded molecules might be concealed by a very broad main resonance line. Further experimental works such as small-angle x-ray diffraction and electron microscopy will be necessary to establish the condi-tions for folding phenomenon and to confirm the certain existence of folded crystals. Less
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