Resonant Raman study of polyparaphenylene-based carbons

A resonant Raman study of polyparaphenylene (PPP) prepared by the Kovacic a nd the Yamamoto methods and heat-treated at temperatures T-HT between 650 a nd 750 degrees C has been performed using different laser excitation energi es E-laser between 1.92 and 3.05 eV. For samples treated at low T-HT, the R aman spectra change with E-laser, and this behavior is ascribed to the coex istence of two forms of the PPP polymer (benzenoid and quinoid) as well as a disordered carbon material. For higher T-HT samples, only a dispersion of the position of the Raman band as a function of E-laser is observed, and t his is explained as due to the carbonization of the original polymer. The t ransition temperature between these two regions of resonance behavior is lo wer for the Yamamoto-PPP samples than for the Kovacic-PPP samples.