MALDI-TOF INVESTIGATION OF PHOTO-DEGRADATION MECHANISMS IN ALIPHATIC POLYESTERS

Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-TOF-MS) has been found to be an excellent method to determine the structure of the molecules produced in the photo-oxidative degradation of poly(butylene succinate) (PBSu) at 60°C in air. Over 20 compounds are present in the MALDI spectrum of the oxidized sample, as compared to only four in the original PBSu sample. The MALDI spectra present many new well-resolved peaks, which provide information on the structure and end groups of the oxidation products. The MALDI peaks correspond to sodiated ions of oxidized oligomers, and they have been assigned to polymer chains containing succinic and malonic acid, butyl-ester, ethyl-ester and butyl formate end groups. These oligomers had not been revealed before. The mechanisms accounting for the formation of photo-oxidation products of PBSu involve the operation of several reactions: i) oxidation of hydroxyl end groups; ii) ?-H abstraction decomposition; iii) Norrish I photo-cleavage. Our results establish the photo-oxidation mechanisms of PBSu. The peculiarity of our approach consists in using a non-averaging technique, such as mass spectrometry, which allows the detection of individual compounds formed during the oxidation process. This is a remarkable result and it should be expected that future MALDI studies might have an impact on the current views on photo-oxidation processes of other polymer systems.