ASAP and DART mass spectrometry analysis for the understanding of polymers degradation mechanisms.

International audienceBecause of the wide range of formulations, a same class of polymer can have different applications. According to the wanted properties, the nature and concentration of the monomers for copolymer, average molar mass of the polymer and nature and concentration of the additives, can be adjusted. In the area of polymers analysis, one of the most important interest is to develop analytical methods allowing a fast and complete characterization of its chemical structure, in particular, in the aim to follow and understand their degradation mechanisms. The ability to detect crude polymers without sample treatment, by using ambient ionization techniques, presents an important advantage. Several techniques, like Atmospheric Solid Probe Analysis (ASAP) and Direct Analysis in Real Time (DART) sources, have been developed to ionize molecules directly from sample for a rapid analysis, without any sample preparation. In this study, both techniques are used for the characterization of two industrial polymers, the polyurethane (PUR) and the polyethylene, using a single time of flight (TOF) analyzer. As copolymer, PUR is difficult to analyze directly by mass spectrometry without preliminary dissociation of each segment from the copolymer. As aliphatic polymer without organic function, polyethylene is also usually difficult to detect by mass spectrometry.DART desorption/ionization technique presents the advantage to show mass spectra of additives with good intensity and without in-source dissociation. However, the polymer detection is more difficult and remains easier by ASAP technique. Indeed, high temperature of gas over the ASAP probe can desorb high molar mass polymers. Pyrolysis products also produced by ASAP can help for polymer identification. Moreover, application of a temperature gradient on the ASAP probe allows a temporal separation of the molecules in function of their volatilization and/or degradation temperature the additives in a first step, and then the segment(s) of the (co)polymer in a second step. ASAP can also create in-source dissociation, increasing mass spectra complexity, but allowing structural identification of polymer and additives by low energy source fragmentation. Thus, these results compare and contrast these two complementary thermal-based ionization techniques for the study of crude polymer directly on the sample. These two sources allow to help to follow and understand chemical modification of the polymer under different stresses, for example under irradiation under oxidative conditions