Thermal degradation of poly(aryl-ether-ether-ketone) (PEEK) was investigated using stepwise pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS) by consecutively heating the sample at fixed temperature intervals to achieve narrow temperature pyrolysis conditions. The individual mass chromatograms of the various pyrolysis products were correlated with the pyrolysis temperature in order to elucidate the pyrolysis mechanism. 4-Phenoxyphenol and 1,4-diphenoxybenzene were detected at 450°C, indicating that the degradation of PEEK was initiated by selective cleavage at chain ends and chain branches. Phenol was detected as the major pyrolysis product by further pyrolysis to 650 °C, which was attributed to the random main chain cleavage of ether groups. At temperatures above 650 °C, chain cleavage at carbonyl ends became the dominant pyrolysis pathway. The high char yield suggested that random main chain scission was accompanied by carbonization. Carbonization was presumably the dominant pyrolysis mechanism at temperatures above 750°C. Results obtained with the new method indicate the interesting potentials of the technique for the investigation of polymeric materials. © 1997 John Wiley & Sons, Ltd. Received 15 August 1997; Revised 17 October 1997; Accepted 20 October 1997 Rapid Commun. Mass Spectrom. 11, 1987-1995(1997 Pyrolysis uses heat alone to break down large molecules into molecules of lower mass due to thermal fission and, occasionally, of higher mass due to intermolecular reaction. The nature of the fragmentation and recombination products is determined largely by the heating parameters and ambient conditions. The analysis of pyrolysis products (pyrolysates) thus provides an alternative means to study polymeric and complex materials that are not suitable for direct analysis by popular techniques such as chromatography and mass spectrometry. From an analytical viewpoint, the applications of analytical pyrolysis are limited by the complexity of the pyrolysates. As a result, the integration of pyrolysis with Fourier transform infrared spectroscopy (Py/FTIR), mass spectrometry (Py/MS), and gas chromatography (Py/GC) is necessary for the routine analysis of polymeric and complex materials. Py/MS offers the advantages of the speed of analysis, the ease of automated data processing, and the richness in chemical information. Py/GC is capable of separating isomers and is a useful tool for quantitative analysis. The integration of pyrolysis with GC/MS (Py/GC/MS) could therefore provide additional sensitivity and selectivity, and extend the application fields of pyrolysis.
The pyrolysis (Py)-GC-MS technique was first introduced for the identification of two kinds of Chinese geographical indication vinegars because its advantages are that it is a simple and convenient sample pretreatment and inlet method. Abundant Py information about vinegars was obtained using Py-GC-MS; 21 common peaks were selected. With the help of the classical partial least-squares (PLS) modeling method for data analysis, two identification models for Shanxi extra-aged (SX) and Zhenjiang (ZJ) vinegars were established, respectively. An N-reducing method was used to select the variables. The variables were reduced one at a time to build the PLS models with the lowest number of misjudgments. Both models had good recognition rates, identifying over 90% of samples correctly. Thus, combining Py-GC-MS and PLS could be regarded as an effective method for the identification of SX and ZJ vinegars.
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