A New View of the Initiation and Propagation in Anionic Polymerization

Abstract

This work confirms the new view of the initiation and propagation mechanism of the anionic polymerization previously proposed, based on the investigation of anionic bulk-polymerization of styrene and α-methyl styrene with the help of a self designed microflow device and characterized by GPC and in situ 7 Li NMR. It was found that n-BuLi tended to form the hexameric-aggregated structure and even to form the huge aggregated structure based on the former. These aggregations of initiators could directly initiate the anionic polymerization and form the supramolecule aggregations. The supramolecule aggregations inevitably blocked the diffusion of the monomers to the ion-pairs and resulted in a stationary-conversion platform. Then the aggregators were dissociated completely into equal binary-aggregated species, and the polymerization continued again rapidly before the termination. Tetrahydrofuran (THF) acted as the electron donator, which could push the electron cloud to Li cation and make the aggregated ring of the active species rather loosened and facilitated the monomer to insert in. Therefore, a little THF can greatly promote the anionic polymerization. However, further addition of THF might block the channel between the ion-pairs and decrease the propagation rate. It was also found that the aggregated structure of the active species during the anionic polymerization only depends on the initiator aggregations which were formed before the polymerization.

Synthesis of poly(n-hexyl methacrylate)-b-poly(methyl methacrylate)viaanionic polymerization witht-BuOK as the initiator at ambient temperature

“…19 Actually, it was found in previous studies that associated initiator could also initiate polymerization. [20][21][22]28,29 Combined with the results above, we infer that t-BuOK exists in different types of associations and ion-pairs when dissolved in THF. All states of t-BuOK can initiate polymerization, but the reactivity for small association state and ion-pairs is much faster than that of big association state because of steric effect (Fig.…”

“…In order to further understand the initiation and side reaction mechanisms of anionic polymerization and broaden the types of monomers, researchers in our laboratory performed a lot of studies and made some progress. For example, Guan et al [20][21][22] researched the initiation mechanism of n-butyllithium (n-BuLi) during the association and dissociation processes. Zheng et al 23,24 synthesized a compound called "P-Complex", which can be dissolved in polar solvent and control side reactions in anionic polymerization of MMA and its copolymers.…”

Styrene/butadiene copolymer synthesized by reactive extrusion

“…On the other hand, the absorption peaks of St unit and Bd unit in the SBR2 are almost the same as those in PS and PB, which means there hardly exists the alternated unit of two monomers in SBR2. The addition of THF also changed the insert structure of Bd and the proportion of 1,2-Bd became larger [15,16] . The structure of the two polymers was quite different only for that two different kinds of feeding sequence were used.…”