PRIMARY THERMAL-DEGRADATION PROCESSES OF POLY(ETHER KETONE) AND POLY(ETHER KETONE) POLY(ETHER-SULFONE) COPOLYMERS INVESTIGATED BY DIRECT PYROLYSIS MASS-SPECTROMETRY

The mechanisms of thermal degradation of poly(ether-ketone) (PEK) and four poly(ether-ketone)/poly(ether-sulfone) copolymers (PEK/PES) have been investigated by direct pyrolysis-mass spectrometry (DPMS). Severa l families of pyrolysis compounds with H, OH and CHO end-groups have b een identified in the pyrolysis mass spectra of PEK. All these pyrolys is compounds can arise from degradation mechanisms involving cleavages of the bridged groups (diphenyl ether and dibenzophenone units). Our data show that the main degradation products of PEK are aldehydes, mos t likely formed by an intramolecular thermal cleavage of benzophenone units. Compounds containing dibenzofuran units have also been observed in the DCI mass spectrum of PEK. The thermal decomposition of a low m olecular weight PEK sample occurs in two stages with the maxima of dec omposition at 390-degrees-C and 490-degrees-C, respectively. This fact indicates the occurrence of an end-group initiated thermal decomposit ion in the early degradation stage which is not present in the case of the high molecular weight PEK sample. The pyrolysis of PEK does not p roduce compounds containing biphenyl units, indicating that extrusion of carbonyls or recominbation processes are not involved. The thermal degradation compounds of the PEK/PES copolymers originate from the the rmal cleavage of the bridge groups (diphenyl ether, benzophenone and d iphenyl sulfone). The pyrolysis mass spectra of 1 : 1 (alt.), 1 : 1 (r andom), 3 : 1 and 1 : 3 PEK/PES copolymers appear essentially identica l (apart for obvious differences in peak intensities), indicating that the molecular rearrangements (SO2 extrusion, transesterification, cle avage of bridges) which occur at higher temperatures and/or in the pyr olysis processes are able to randomize the distribution of comonomer u nits originally present in the copolymers. Differences in peak intensi ties have been found to reflect almost quantitatively the molar compos ition of the copolymers.