1991 Fiscal Year Final Research Report Summary
Analysis of thermal transition of polymers by positron annihilation.
| Project/Area Number |
02453059
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
工業分析化学
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| Research Institution | The University of Tokyo |
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Principal Investigator |
UJIHIRA Yusuki Professor Research Associate, 工学部, 教授 (40010805)
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| Co-Investigator(Kenkyū-buntansha) |
KOBAYASI Yosinori Chemical Research Institute, 主任研究管
UEDONO Akira Research Associate, 工学部, 助手 (20213374)
NOMURA Kiyosi Senior Research Staff, 工学部, 助手 (40124680)
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| Project Period (FY) |
1990 – 1991
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| Keywords | positron annihilation / ortho-positronium / free volume / polymer / polyethylene / polyvinyl alcohol / epoxy resin / polypropylene |
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| Research Abstract |
Life time parameters of positron and positronium can give direct information on the content and size of free volume present in amorphous materials such as polymers. The variation of life times (tau_1, tau_2, tau_3, tau_4) and their intensities (I_1, I_2, I_3, I_4), obtained by the deconvolution of positron annihilation spectra. in terms of temperature for polyethlene, polypropylene and epoxy were observed and critical discussion were given on the explanation of life time parameters obtained. The results of temperature dependence of I_4 (intensities of opositronium --o-Ps--formed in the free volume of polyethlene and polypropylene), revealed that the concentration of free volumes increased drastically at the melting temperature, whereas gradual increase of tau_4 (life time of o-Ps formed in the free volume) from 2.9 to 3.5 ns indicating monotonous inflation of free volumes. The scarce changes of free volume in polyethlene as a function of molecular weight are confirmed.
The thermal cycle experiments using two parametric temperature-life time apparatus. revealed that the polyethlene and polypropylene showed reversible I_4 behavior against thermal cycles. The retention of mechanical strain in the samples gives discrepancy of I_4 behavior from reversible curve. Life time spectra of degassed thin pellet of copolymer composed of vinyl alcohol (80- 100 mol%) and vinyl acetate. were decomposed to three components. Although I_3^!s do not change but tau_3 decreases with the degree of polymerization (n=45- 2500) and saponification. indicating that every free volume becomes smaller as the process of crosslinking. Both tau_3 andI_3 of PVA (N= 45 and 2000) varied between 20-200ﾟC.
Relation between free volume of epoxy and concentration of net network revealed that epoxy cured at 50ﾟC has more uniform and smaller free volume than that of cured at 100ﾟC. It means bigger free volume are produced in more rapid crosslinked epoxy even if net network concentration is same.
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