Controlled High-Speed Anionic Polymerization of Propylene Oxide Initiated by Onium Salts in the Presence of Triisobutylaluminum

Abstract

The conventional anionic polymerization of propylene oxide (POx) proceeds at a very slow rate in low polar media and is characterized by an important transfer reaction to monomer. This only allows the formation of poly(propylene oxide) oligomers. A new polymerization strategy allowing the fast and controlled anionic polymerization of POx has been developed. It is based on the formation of complexes with both the anionic initiator and the monomer. The influences of alkali metal alkoxides (i-PrONa), ammonium salts (NBu4Cl and NOct4Br), and phosphonium salts (PBu4Cl) as initiators, in combination with triisobutylaluminum, have been investigated in terms of reactivity, molar mass control, livingness, and polymerization mechanism. PPOx with narrow polydispersities and controlled molar masses, up to 150 000 g/mol, have been obtained in hydrocarbon media, at low temperature, and in short reaction times.

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

“…Polymerization of Ethoxyethyl Glycidyl ether and t-butyl Glycidyl Ether A binary initiating system constituted of NOct 4 Br as initiator and i-Bu 3 Al as catalyst/activator has been recently reported by us for the controlled anionic polymerization of epoxides [30][31][32][33] in hydrocarbon media. This system was investigated for the polymerization of EEGE and t-BuGE, as a protected form of glycidol.…”

“…This suggests an apparent zero monomer order for the propagation reaction as already proposed for the monomer-activated mechanism of propylene oxide. [30] Compared to EEGE, polymerization of tBuGE proceeds more readily and goes to completion in a few hours using only 2 equivalents of triisobutylaluminum with respect to the tetraoctylammonium bromide initiator. This can be explained by the presence of a single oxygen atom on the tBuGE and on PtBuGE units, without counting the oxygen atom of the reactive and reacted epoxide function, which is moreover greatly hindered by its tert-butyl substituent.…”

“…Some broadening can be attributed to the high NOct 4 Br/i-Bu 3 Al ratio used (1/5), necessary to quantitatively polymerize EEGE, which induces a very high reactivity for POx and results in a slight contribution of transfer reaction. [30] The reactivity ratios between EEGE and POx were determined in a series of copolymerization experiments stopped at low conversion, using the Kelen-Tudö s method. [34] This yields r POx ¼ k POxPOx /k POxPEEGE ¼ 3.58 and r PEEGE ¼ k PEEGEPEEGE /k PEEGEPOx ¼ 0.18 indicating, in living-like conditions, the formation of copolymers with a gradient composition constituted by a predominant incorporation of POx units at the beginning of the chains and EEGE units at the end.…”

“…[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.…”