Chemical structural characterization of pyrolyzed and subsequently ion-implanted poly(acrylonitrile)

Infrared (IR), Auger electron spectroscopy (AES) and X-ray photoelectron spectra (XPS) of pristine, pyrolyzed, and ion-implanted poly(acrylonitrite) (PAN) samples were obtained in order to correlate the structural changes accompanying pyrolysis and implantation with the electrical properties of the respective PAN products. The results show that PAN is first converted to a polyconjugated heterocyclic ladder structure at a temperature of 435 °C and then to a graphite-like structure at temperature above 750 °C. Pyrolysis studies took place in a temperature range of 350–750 °C. IR studies showed that upon heat treatment at 435 °C, major structural changes occur as indicated by the complete disappearance of the nitrile and methylene absorption bands and the formation of new bands. The degree of conjugation in pyrolyzed PAN can be selectively controlled by the proper choice of the heat treatment temperature. From the studies, ion implantation causes extensive nitrogen depletion and the nitrogen chemical state in the implanted sample is different from that found in the pyrolyzed materials. Upon ion implantation, the component assigned to the nitrogen in a sigma bonding state (401.27 eV) increased in intensity (46%) relative to the intensity (27%) of the component for which nitrogen is in a hetroaromatic structure. Both AES and XPS analysis showed the variation of C:N ratio as a function of heat treatment.