Live monitoring of anionic living polymerizations by electrospray-ionization mass spectrometry.

Abstract

Anionic polymerizations are of exceptional practical importance, but difficult to analyze due to the high reactivity of the growing polymer chains. Here, we demonstrate that electrospray-ionization mass spectrometry (ESI-MS) permits the direct observation of the active carbanionic intermediates formed in the anionic ring-opening polymerization of 1-cyanocyclopropane-carboxylate in tetrahydrofuran. This includes the identification of a side product, as well as the real-time analysis of the polymerization reaction. From the obtained mass spectra, we can derive not only the mean molar mass and the polydispersity, but also the rate constants for the initiation and the individual propagation steps. The initation proceeds significantly faster than the propagation steps. Accordingly, the examined reaction corresponds to a living polymerization, as we also confirmed by additional control experiments. Besides giving detailed insight into the reaction system probed here, we expect the presented methodology to make possible the in-situ analysis of further anionic polymerizations as well.