1P-10 PDF
Structural characterization of polymethoxymethylsiloxanes by electrospray ionization (tandem) mass spectrometry
Poly(methoxymethylsiloxane)s (PMMS) are silicon-based prepolymers of industrial interest as crosslinking agents or for the preparation of nanoparticles (improving the thermal and mechanical properties of elastomers) but prepared by a poorly controlled synthesis route yielding samples of high structural dispersity.
Collision induced dissociation of PMMS was hence studied in details in order to propose MS/MS rules to be usefully employed for a detailed microstructural characterization. Lithium adduction did not provide meaningful insights through charge remote fragmentations while ammonium adduction allowed PMMS to readily dissociate according to two main information-rich charge driven routes. On one hand, after precursor ions have eliminated methanol together with ammonia, a series of 46 Da (CH2O+CH4) losses was observed, the number of which could be used to decipher the polymerization degree of the dissociating precursor. On the other hand, cleavage of Si–O bonds in the polymer backbone generated an incomplete series of product ions of low m/z values, containing one or the other end-group (found to be methoxy or tetramethoxytetramethylcyclotetrasiloxy) terminations. Proposed mechanisms were all supported by accurate mass measurements and MS3 experiments. Based on these two complementary routes, the main species of a PMMS sample were thoroughly characterized, allowing unique insights into the synthesis mechanism.