PYROLYTIC BEHAVIOR AND IN-SITU PARAMAGNETISM OF STAR-LIKE C-60(CH3)(X)(PAN)(X) COPOLYMERS

The n-butyl-terminated polyacrylonitrile (PAN) and novel Caa(CH,),(PAN ), copolymers have been pyrolyzed under vacuum, between 25 and 475 deg rees C. The in-situ infrared absorption measurements demonstrated that the nitrile groups of the polymers disappear gradually as heating pro gresses, and conjugated C=N chains appear. As pyrolysis proceeds, evid ence for aromatic ring formation is found. Below 200 degrees C, a smal l portion of the nitrile groups begins to form conjugated chains. In c onsideration of the existence of the strong steric hindrance effect an d dipole and electric effects in the copolymer, a reasonable pyrolysis scheme is suggested. The in-situ paramagnetism has been investigated using the variable-temperature ESR technique. The unique temperature d ependence of the ESR spectra is very intriguing. These results indicat e the evolution of radical sites during pyrolysis and the delocalizati on of carriers, as well as the formation of conjugated double bonds by pyrolytic modification. Finally, the morphological structure and elec tric properties of the above samples and their pyrolytic products are also described. (C) 1998 Elsevier Science Ltd. All rights reserved.