CHAIN-END CONTRIBUTION IN STATIC SECONDARY-ION MASS-SPECTROMETRY OF OLIGOMERIC POLY(ETHYLENE GLYCOLS)

Poly(ethylene glycols) (PEGs) of a variety of molecular weights rangin g from a few hundred Da to 900 kDa, terminated with a range of functio nal groups, were cast as thin films and examined by static secondary i on mass spectrometry (SSIMS). The intensities of ions in the SSIMS spe ctra are examined and it is demonstrated that the m/z 45 ion relative intensity (compared to the m/z 43 intensity) for hydroxy-terminated PE Gs increases from 68% at very high molecular weight to 84% at 2 kDa an d below. Those PEGs terminated with deuteroxy groups demonstrate a str ong ion at m/z 46 at low molecular weight, which indicates that the m/ z 45 intensity in hydroxy-PEG is strongly influenced by the presence o f terminal groups in the PEG film. It is shown that amino- and methoxy -terminated PEGs have a similar mit 45 relative intensity to high-mole cular-weight PEG, suggesting that hydrogen abstraction in these system s does not occur to any great extent and the excess intensity at m/z 4 5 for hydroxy-PEG derives from fragment ions formed by the direct clea vage of polymer end groups.