Sequence distribution of poly(ether-sulfone) poly(ether-ketone) copolymers by mass-spectrometry and C-13 NMR

The sequence distributions of four poly(ether-sulfone)/poly(ether-ketone) (PES/PEK) copolymer samples were determined by means of fast atom bombardment mass spectrometry (FAR-MS) and by C-13 NMR spectroscopy. The controlled partial degradation of the copolymer chains to produce oligomers suitable of FAB-MS analysis was performed with sodium methoxide in dimethyl sulfoxide solution at 130 degrees C, and the experimental conditions were optimized. The sequential arrangements of ether-sulfone/ether-ketone units present in these materials were estimated by a best-fit minimization method using the MACO4 computer program which compares the experimental FAB-MS spectral intensities with theoretical intensities. Random PES/PEK copolymer samples showed quite the same sequence arrangements as expected from monomer feed-ratios used in the syntheses. Instead, a PES/PEK copolymer sample expected to be exactly alternating (from the synthesis procedure) showed 44% of random sequences owing to the transetherification reaction which occurred in the synthesis. The results of sequential analysis obtained from C-13 NMR data compare well with the data obtained by the FAB-MS analysis.