A solid-state NMR study of the carbonization of polyaniline

N-15-labeled polyaniline (PANI) is heat treated at temperatures from 200 to 1000 degrees C in a nitrogen atmosphere. The carbonization of PANI is determined using solid state (SS) C-13 and N-15 NMR. In an attempt to accurately assign the experimentally observed N-15 NMR chemical shift, theoretical nitrogen shielding is calculated using ab initio MO calculations. The SS NMR results imply that the reconstruction of the polymer backbone occurs in the temperature range 400-600 degrees C and the nitrogen of Phe-NH-Phe amino group changes to pyrrolic or tertiary nitrogen and the imine nitrogen changes to pyridinic nitrogen. Heat-treatment above 700 degrees C leads to a decrease in the number of five-membered rings containing nitrogen atoms (pyrrolic), while the number of six-membered rings containing nitrogen (pyridinic, pyridineoxide and pridinium) increases. (C) 2012 Elsevier Ltd. All rights reserved.