Static SIMS spectra of polystyrene obtained by ‘living’ radical polymerization. Part I: Molecular weight-dependent fragmentation

✍ Scribed by Vanden Eynde, X.; Matyjaszewski, K.; Bertrand, P.

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 332 KB
• Volume: 26
• Category: Article
• ISSN: 0142-2421
• DOI: 10.1002/(sici)1096-9918(199807)26:8<569::aid-sia403>3.0.co;2-2

✦ Synopsis

A series of low-polydispersity polystyrenes with molecular weight ranging from 2000 to 130 000 were synthesized by atom transfer radical polymerization and analyzed by time-of-Ñight secondary ion mass spectrometry. The end groups obtained by this polymerization process were hydrogen at one end and bromine at the other end. The molecular structure of the end groups and the molecular weight of the chains were found to inÑuence signiÐcantly the absolute intensities of the end-group parent ions and the characteristic polystyrene fragments. For their formation, two di †erent mechanisms have to be taken into account : direct scission and rearrangement before the emission.

The absolute intensities of the end-group fragments in positive and negative modes exhibit a decrease when the molecular weight decreases. The protonated repeat unit fragments ( [ M + H ] ' or at m/z = 105) and C 8 H 9 ' bromide ions (Br-at m/z = 79 and 81) are produced by a direct scission mechanism of the respective end groups. Meanwhile, the tropylium ion intensity at m/z = 91) increases for the low-molecular-weight samples. (C 7 H 7 ' (M n ) This ion cannot be produced by a direct scission but a reorganization process of the polymer structure is required before the fragment emission.

It is shown that, in static SIMS, the sensitivity towards the end group and then towards the molecular weight is dependent on the stability, the electroaffinity and/or the ionization potential of the ions formed from the end group.