MALDI Investigation of Photooxidation in Aliphatic Polyesters: Poly(butylene succinate)

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS) has been found to be an excellent method to det. the structure of the mols. produced in the photooxidative degrdn. of poly(butylene succinate) (PBSu) at 60 °C in air. Over 20 compds. are present in the MALDI spectrum of the oxidized sample, as compared to only 4 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 oxidn. products. The MALDI peaks correspond to sodiated ions of oxidized oligomers, and they have been assigned to polymer chains contg. succinic and malonic acid, Bu ester, Et ester, and Bu formate end groups. These oligomers had not been revealed before. The mechanisms accounting for the formation of photooxidn. products of PBSu involve the operation of several reactions: (i) oxidn. of hydroxyl end groups; (ii) a-H abstraction decompn.; (iii) Norrish I photocleavage. Our results establish the photooxidn. mechanisms of PBSu. The novelty of our approach consists of using a nonaveraging technique, such as mass spectrometry, which allows the detection of individual compds. formed during the oxidn. process. This is a remarkable result, and it should be expected that future MALDI studies might have an impact on the current views on photooxidn. processes of other polymer systems.