IR spectral investigation of the pyrolysis of polymer precursor to diamond-like carbon

Structural changes occurring during pyrolysis of the polymer [C₆H₅C]_n (phenylcarbyne), synthesized by an ultrasonic chemical method, were investigated using IR spectra. IR absorption spectra in the wavenumber range 400-4600 cm^-1 were measured and analyzed. Analysis of the spectral data indicated that O-H, C-H, C=C, C=O, C-O-C stretching bonds etc. existed in the polymer, which suggested that the phenyl ring and impurities (water, methane, tetrahydrofuran, etc.) may be present in the polymer. The IR characteristics of the polymer showed a dependence on the temperature of pyrolysis. When the temperature was below 400 °C, the powder was a hydrocarbon polymer with IR absorption indicating several kinds of bands similar to those of the original polymer; when the temperature was between 400 and 600 °C, thermal decomposition of the polymer occurred, resulting in a reduction in intensity of various IR absorption bands; an increase in the temperature above 600 °C resulted in the conversion to diamond-like carbon (DLC), showing only a few IR absorption bands (O-H, C-H, C=C, C=O). It is proposed that the structural changes of the polymer during pyrolysis were due to the evolution of the phenyl ring and impurities (hydrogen, etc.) in the polymer.