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Abstract No.: ThP-213
Session: Polymer Characterization
Presentation date: Thu, Aug 31, 2006
Presentation time: 09:50 – 11:20

Thermal Oxidative Degradation of Polyethylene Glycol

Helge Egsgaard1, Martin Nordvig Mortensen2, Soeren Hvilsted3, Jens Glastrup2

1 Risoe National Laboratory, Biosystems Department, Roskilde, Denmark
2 The National Museum of Denmark, Department of Conservation, Lyngby, Denmark
3 Technical University of Denmark, Danish Polymer Centre, Lynby, Denmark

Correspondence address: Helge Egsgaard, Risoe National Laboratory, Biosystems Department, Frederiksborgvej 399, Roskilde, DK-4000 Denmark.

Keywords: Electrospray Ionization (ESI); MALDI; Polyethylene Glycols; Polymer.

Novel aspect: The degradation of intact polymers has been studied using soft ionization and MS/MS mass spectrometry. Slow degradation seems to be reflected primarily by reduced molecular weight of the PEG and an increased dispersion.

 

Polyethylene glycol (PEG) has a widespread use either as a homopolymer or as a component of copolymers. In addition, PEG finds a number of unique applications, e.g. PEG is by far the most used conservation material in the conservation of archaeological wood that needs to be dimensionally stabilized. The degradation of PEG is therefore of considerable practical interest.

The products of the thermal and oxidative degradation of PEG have previously been studied by advanced NMR techniques. The major result of degradation was found to be chain scission resulting in formate esters. Minor products were in-chain esters, peroxy groups, oxymethylene links and methoxy chain ends. It appears that related studies by mass spectrometry have not been performed. Thus, we decided to degrade PEG 1500 at 90 °C in dry air and analyze the reaction mixture by ESI and MALDI mass spectrometry. The aim was to identify structures, which could be used as indicators for thermal and oxidative degradation of PEG.

The spectra demonstrate clearly that a broad pallet of products is formed. Structural information was obtained from MSn spectra using ions generated by ESI. The spectra were rationalized by comparison to reference structures.

Unfortunately, many products appeared to be isobaric, e.g. in chain esters and PEG-OMe. In addition, most products seem to be prone to hydrolysis. This leaves very few high-molecular-weight candidates to be used safely as indicators for the thermal and oxidative degradation. Thus, slow degradation seems to be reflected primarily by reduced average molecular weight of the PEG, increased dispersion and by the presence of an increased amount of free or ester bound formic acid.