Cationization of dendritic macromolecule adsorbates on metals studied by time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was utilized to study dendritic macromolecules with various architectures, such as dendrons, dendrimers and hyperbranched polyesters prepared from bis-(hydroxymethyl)propionic acid (Bis-MPA) and a series of hyperbranched polyethers based on 3-ethyl-3(hydroxymethyl)oxetane. The measurements were performed on spin-coated thin films of the branched molecules (D) onto silicon, chemically etched copper foil and silver-coated wafers. They showed weak signatures of molecular ions by proton capture (D + H)(+) in the high mass range of the spectra (m/z > 400). On the contrary, cationization of the intact molecules with alkali or transition metal ions such as Na+, Cu+ or Ag+ was observed. High-intensity quasi-molecular ions (D + M)(+) (with M = Na+, Cu+ or Ag+) allowed the studied polymers to be identified. The whole molecular species were observed for Bis-MPA dendrons and dendrimers up to 3000 Da for hydroxyl or acetonide-terminated derivatives. The success of the so-called cationization experiments with metal substrates compared with analysis of molecular adsorbates on silicon is highlighted. The ToF-SIMS sensitivity appeared useful to provide information about the molecular end-groups or to highlight incomplete reaction occurring during some deprotection step of the synthesis. Only uncationized fragments of low masses were detected for the hyperbranched polyesters. This result suggested the effect of molecular asymmetry and/or flattening of the molecules on the substrates, which hampered the molecule lift-off efficiency. Nevertheless, the hyperbranched polyethers were characterized based on the peak distribution of intensities, which allowed estimation of their molecular weight average. This work was intended to illustrate the capabilities of ToF-SIMS to analyse dendritic polymers on surfaces. Copyright (C) 2003 John Wiley Sons, Ltd.