Optical studies of pyrolyzed polyacrylonitrile

Authors

  • T.-C. Chung,

    1. Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104
    Current affiliation:
    1. Department of Physics, UCSB, Santa Barbara, California 93106
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    • Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104;

  • Y. Schlesinger,

    1. Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104
    Current affiliation:
    1. Department of Phisics, Bar-Ilan Univdrsity, Ramat-Gan, Israel
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    • Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104;

  • S. Etemad,

    1. Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104
    Current affiliation:
    1. Bell Laboratories, Whippany, New Jersy
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    • Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104;

  • A. G. Macdiarmid,

    1. Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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    • Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104;

  • A. J. Heeger

    1. Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104
    Current affiliation:
    1. Department of Physics, UCSB, Santa Barbara, California 93106
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    • Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104;


Abstract

The results of measurements of the optical absorption spectra, IR absorption spectra, thermogravimetric analysis, and elementary analysis of pyrolyzed polyacrilonitrile are presented as a function of the pyrolysis temperature Tp and of the duration of pyrolysis. At Tp ∼ 200°C, an intermediate phase was discovered, containing conjugated CN sequences and a completely unreacted carbon backbone. The optical absorption data imply that the resulting polymer is a semiconductor with a delocalized π-electron system and an energy gap Eg ⋍ 2.5 eV. For Tp > 260°C, the weight loss rapidly increases, and the absorption edge gradually broadens and shifts to lower energies. The resulting polymer (after higher-temperature pyrolysis) contains CN and C[DOUBLE BOND]C[BOND]C conjugation sequences, but appears to be a complex structure consisting of a mixture of different chemical species.

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