“Controlled” High-Speed Anionic Polymerization of Propylene Oxide Initiated by Alkali Metal Alkoxide/Trialkylaluminum Systems

Abstract

The anionic polymerization of propylene oxide initiated by alkali metal alkoxide suffers from several drawbacks such as a slow polymerization rate in nonpolar solvents and an important chain transfer reaction to monomer. We found that the addition of trialkylaluminum to the alkali metal alkoxide/ propylene oxide system in hydrocarbon media strongly enhances the polymerization rate and strongly reduces the transfer reactions, thus allowing the controlled synthesis of poly(propylene oxide) with relatively high molar masses (up to 20 000 g/mol). At constant monomer and alkali metal alkoxide concentrations the polymerization rate increases with increasing trialkylaluminum concentration. Kinetic data and 1 H NMR studies indicate that the trialkylaluminum derivative is involved in the formation of two distinct complexes, one with the alkali metal alkoxide and another with the PO monomer. The strong electron-withdrawing on PO R-carbons associated with AlR 3 complexation makes the monomer much more susceptible to ring opening. Moreover, since the withdrawing effect is much less pronounced on the PO methyl group, the complexation also results in a higher selectivity of the nucleophilic species toward the ring-opening reaction to the detriment of the proton abstraction process yielding transfer to monomer.

Grignard-based anionic ring-opening polymerization of propylene oxide activated by triisobutylaluminum

“…and P2 0 could also be assigned to PPO chains with allyloxy and hydroxide end groups [13,14,42] or even to PPO chains with isobutyl and hydroxide end groups [43,44]. However, looking at the allylic and aliphatic regions of NMR spectra of those polymers, no peak characteristic of respectively transfer to monomer or isobutyl initiation is observed, as also shown in another work [33].…”

Linear High Molar Mass Polyglycidol and its Direct α‐Azido Functionalization

“…[30,32] Although it cannot be precisely quantified the amount of H-PEEGE-OH chains resulting from this side initiation process appears almost negligible as compared to the azido-functionalized ones.…”

Epoxide Activated Anionic Polymerization: Application to the Synthesis of (Co)Polyethers with Controlled Structure and Tuned Properties

“…In recent works we have found that very simple initiators based on the association of alkali metal derivatives [4,5] or tetralkylammonium or tetraalkylphosphonium salts [6] with triisobutylaluminum (i-Bu 3 Al) yield a rapid and controlled polymerization of propylene oxide whereas transfer to monomer was strongly reduced or even suppressed. As it may be seen in Table 1 In contrast, in the presence of an excess of the aluminic compound, polymerization proceeds rapidly, up to complete monomer conversion.…”

“…As it may be seen in Table 1 In contrast, in the presence of an excess of the aluminic compound, polymerization proceeds rapidly, up to complete monomer conversion. In the temperature 4 Cl salts , whereas for a given counterion the polymerization rate directly increases with the amount of trialkylaluminum which acts as an activator/catalyst for the polymerization. Since when initiators are used alone or at ratio initiator/i-Bu 3 Al of 1:1, no polymerization proceeds, these results sustain the selective insertion of a i-Bu 3 Al complexed monomer which is electrophilically activated.…”