Stopping the Chain: Isolated Molecular Intermediates of Anionic Styrene Polymerization

Anionic polymerization developed to one of the most used polymerization techniques both in industry and academia in the last 70 years. Due to the required high reactivity of the polymerization, the isolation of the organometallic intermediate in between initiation and propagation step has not been possible so far and its mechanism is still not fully understood. Additionally, deprotonations in benzylic positions remain challenging, which is a prerequisite for a successful living carbanionic polymerization, but also complicating the synthetic access to the intermediates. Herein, we present the synthesis and isolation of the first-step carbolithiation product of anionic styrene polymerization in diethyl ether and tetrahydrofuran. Characterizations in solid-state by X-ray diffraction and in solution state by extended nuclear magnetic resonance (NMR) experiments were carried out. Differing initiation reactivity was observed by in situ fourier transform-infrared (FT-IR) spectroscopy, revealing the intermediates to be responsible for polymerization reactivity. A possible mechanistic explanation for the initiation state was presented by density functional theory (DFT) calculations. By our approach of isolating the chain-relevant intermediates on a molecular level, we gained new insights on the existing mechanism.