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Investigations on the mechanism of anionic polymerisation

Grafic illustration © AK-Strohmann​/​TU Dortmund

Anionic polymerisation is one of the most important polymerisation techniques, including in the chemical industry. It was first used on an industrial scale in the first half of the 20th century and is still valued today for its ability to adjust polymer properties such as chain length and polydispersity. Despite its great importance and long history, the mechanism of anionic polymerisation has not yet been fully elucidated. We have now succeeded for the first time in isolating and characterising the intermediate of anionic styrene polymerisation. By carefully selecting the conditions, such as the choice of solvent and carrying out the reaction at cold temperatures, we were able to stop the polymerisation immediately after initiation and isolate the intermediate. Single-crystal X-ray structural analysis was used to determine the solid-state structure, which was then confirmed in solution by extended NMR studies. After a ligand exchange reaction, in addition to the first structure obtained of the intermediate of anionic styrene polymerisation with diethyl ether, the important intermediate with THF was also obtained. Subsequent in situ FT-IR experiments enabled a solvent-dependent investigation of the underlying reactivity of the formation of the various intermediates. Additional DFT calculations allowed the proposal of a possible mechanism for the formation of the intermediates based on the structures known from literature. Since the intermediates also exhibit different reaction rates in the polymerisation itself, they must play a central role in the further mechanism of the polymerisation process. Since the isolation of the intermediate now allows the sub-steps of initiation and propagation to be investigated separately for the first time, further research will examine how the propagation of polymerisation can be explained on the basis of the isolated intermediate.

Stopping the Chain: Isolated Molecular Intermediates of Anionic Styrene Polymerization
A. Schmidt, C. Strohmann*,
Angew. Chem. Int. Ed. 2025, e202510397.

„Stopping the Chain“: Isolierte molekulare Zwischenstufen der anionischen Styrolpolymerisation
A. Schmidt, C. Strohmann*,
Angew. Chem. 2025, e202510397.