Chemical transformation during the carbonisation in air and the pyrolysis under argon of a vinylpyridine-divinylbenzene copolymer by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to identify and characterise the nitrogen functional forms present in a vinylpyridine-divinylbenzene copolym er, its chars, obtained by heating in air at different temperatures and the pyrolysates, obtained by heating the different chars at 950 degrees C unde r argon. By fitting the N1s envelope, six component peaks were individualis ed corresponding to a last six different forms of pyridinic nitrogen. The C ls and Ols envelopes were also 'decomposed' which permits to follow the fix ation of oxygen by the polymer during the carbonisation in air as a functio n of the temperature and the subsequent depletion of oxygen during the pyro lysis. It is shown that during the condensation process at high temperature , nitrogen atoms were incorporated in the graphene layers replacing carbon atoms in different positions; at the edge of graphene layers as pyridinic N or in the inside as 'quaternary' heterocyclic N. Upon exposure to the ambi ent pyridone-type N and pyridine oxide can be formed by post-oxidation of t he pyrolysate. The nitrogen content and the distribution of the different f orms of pyridinic nitrogen are identical in the different pyrolysates whate ver the char from which they are derived. (C) 1999 Elsevier Science B.V. Al l rights reserved.