End group structural analysis of polyphenylene sulfide by thermal desorption / pyrolysis DART-TOFMS
MSTips No. 353
Pyrolysis / gas chromatography / mass spectrometry (Py/GC/MS) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) are powerful tools in polymer analysis. Py/GC/MS is a method in which a polymer sample is heated instantaneously and the volatile components generated by thermal decomposition are analyzed by GC-MS. Although it can be applied to polymers in various states and chemical information can be obtained, since the polymer is decomposed to the monomer level, average information of the sample can be obtained, but it is difficult to analyze the end group structure. MALDI can ionize polymers softly, and by selecting an appropriate matrix, it can ionize polymers with a molecular weight of several hundreds Da to several hundreds kDa. By combining with a high-resolution time-of-flight mass analyzer, if the sample has a molecular weight of up to about 10 kDa, a mixture of homopolymers with different end groups, a mixture of dissimilar polymers, or a copolymer can be mass-separated and the molecular weight distribution can be obtained. However, the elemental composition analysis of end groups by means of accurate mass is limited up to several kDa. While there are advantages and disadvantages in polymer analysis by Py/GC/MS and MALDI-MS, end group analysis of polymers by thermal desorption / pyrolysis (TDP) -DART-MS has been proposed [1]. This is a method of analyzing the volatile components generated when the polymer is gradually heated by a thermal desorption / pyrolysis device by using DART-MS.
By gradual heating, unlike Py/GC/MS, moderately fragmented oligomer components can be analyzed by DART-MS. Some of the oligomer components generated include the end group structure by single cleavage of the main chain, which helps to analyze the structure of the polymer. Here, an analysis example of polyphenylene sulfide (PPS) using TDP-DART-MS is reported [2]. PPS is an engineering plastic with excellent heat resistance and chemical resistance. It is important to analyze the structure of the end groups because the difference in the manufacturing method appears in the end groups. However, it was difficult to analyze the end groups of PPS because it is insoluble in general organic solvents.