CHEMICAL MODIFICATION OF POLYPYRROLE .2. THERMAL-STABILITY, DIELECTRIC, AND CONDUCTIVITY CHARACTERISTICS OF POLYPYRROLE SUBSTITUTED WITH PHTHALIC AND PYROMELLITIC DIANHYDRIDE

Polypyrrole (PPY) was electrophilically polycondensed with phthalic anhydride (PA) and pyromellitic dianhydride (PMDA). PPY-PA and PPY-PMDA polycondensates were evaluated in regard to their thermal stability and dielectric and conductivity behavior. The overall thermal stability is in the order PPY < PPY-PA < PPY-PMDA, which may be rationalized in terms of intra- and intermolecularly cross-linked structures of the polycondensates. IR spectral analyses of PPY-PA and PPY-PMDA subjected to heating at 300, 400, 500, and 550 degrees C, respectively, were conducted to understand some of the structural changes in the polymer matrices. Both PPY-PA and PPY-PMDA exhibit high dielectric constants (200 and 125) at low frequency (10(3) Hz), which fall monotonically with increasing frequency, suggesting the possibility of interfacial polarization. The conductivity values of PPY-PA and PPY-PMDA are in the range 10(-3)-10(-4) ohm(-1) cm(-1), which are conspicuously lower than that for unmodified PPY (2.5). This is due to the adverse effect of increasing temperature on the PPY chain stability, whereby structural conjugation and eventually conductivity will be affected. (C) 1994 John Wiley and Sons, Inc.