Characterization of ethanolysis products of poly(dimethylsiloxane) species by electrospray ionization tandem mass spectrometry
Résumé
RATIONALE The partial and controlled degradation of insoluble cross-linked silicon-based polymers is a promising approach to enable their characterization by mass spectrometry. Providing that the chemolysis reaction specifically proceeds at cross-linking sites, the size of linear poly(dimethylsiloxane)s (PDMS) produced during the treatment should reflect the length of linear segments between branching points in the original network. In this context, the specificity of ethanol to act as a nucleophilic agent towards tri-functional silicon atoms in a D3TDnTD3 model was evaluated. METHODS Tandem mass spectrometry (MS/MS) combined with accurate mass measurements, MS3 experiments and collision-induced dissociation of authentic compounds was used for structural characterization of D3TDnTD3 ethanolysis products. All MS/MS data were obtained from electrosprayed ammonium adducts, previously reported to provide the most informative data for silicon-based polymers. RESULTS Since the expected ethanolysis products were hydroxy- and ethoxy-terminated PDMS, the dissociation behavior of such polymeric species was established, using electrosprayed ammonium adducts as the precursor ions. Diagnostic product ions were identified, allowing four main D3TDnTD3 ethanolysis products to be structurally characterized. End-group analysis of these polymeric distributions clearly indicated that ethanolysis was mostly occurring on tri-functional silicon atoms but also, to a lesser extent, on those D atoms close to T silicons. CONCLUSIONS The size of the linear skeleton located between two tri-functional silicon atoms could be accurately determined by mass spectrometric analyses of a polymeric model submitted to ethanolysis. This soft and rapid pre-treatment is thus a promising approach for determining the length of linear segments between branching points in the original network of cross-linked silicon-based polymers. Copyright (C) 2012 John Wiley & Sons, Ltd.