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Retrograde Depolymerization in Living Anionic Polymerization of α-Methylstyrene
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DOI：10.1021/acs.macromol.5c00964.png)
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Abstract
En 中文
α-Methylstyrene (AMS) displays anomalous behavior in living anionic polymerization, undergoing spontaneous depolymerization under typical conditions. This phenomenon contradicts the prevailing steric strain hypothesis for α-methyl-induced depolymerization as prior mechanistic interpretations lacked experimental verification and failed to explain chain-end migration processes. We developed a strategy combining vinyl deuterium-labeled AMS (AMS-d2) with in situ variable-temperature NMR to resolve these contradictions. This approach revealed the nonparticipation of the α-methyl group in depolymerization. Sequential time sampling of poly(AMS)-Li (PAMS-Li) chains demonstrated a stepwise monomer unit detachment rather than random chain cleavage. Through strategic modification of chain-end structures using electron-donating/withdrawing substituents and homopolymerization of long-chain monomers, we established a definitive depolymerization mechanism involving a metastable four-membered ring transition state between the terminal carbanion and the penultimate monomer unit. This transition state enables concerted carbanion migration and monomer release. The findings provide fundamental insights into AMS retrograde polymerization and form a foundation for the rational design of AMS-based polymers with tailored depolymerization properties.