Characterization of the vulcanization products of squalene by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: model studies on the vulcanization of natural rubber

A method for the characterization of the vulcanization reaction products of squalene using matrix-assisted laser desorption/ionization time-of-night m ass spectrometry (MALDI-TOFMS) was developed. Squalene was chosen as a mode l molecule for natural rubber. Different matrix-solvent pairs were evaluate d with the spectrometer functioning in the linear mode, working with positi ve/negative high voltages and different laser powers. The study led to the following important conclusions. The identification of squalene requires a cationizing agent whereas the identification of the two families of curing systems used, a sulfenamide and a thiuram, requires only the use of a matri x (dithranol and dihydroxybenzoic acid, respectively). For the first time, the intermediate compounds such as squalene derivatives with pendant sulfur -containing groups and interacting with zinc as well as cross-linked squale ne were identified. Only a matrix is required and the solvent acetonitrile leads to better spectra than THF (which oligomerizes during sample preparat ion). Adequate sample treatment is critical to the success of the method. S uitable conditions were found for the characterization of the vulcanization reaction. MALDI-TOFMS appears to be an important tool for the analysis and deconvolution of the mechanisms of the vulcanization of natural rubber. Co pyright (C) 2001 John Wiley & Sons, Ltd.