Combination of phosphazene base and triisobutylaluminum for the rapid synthesis of polyhydroxy telechelic poly(propylene oxide)

Abstract

Anionic ring-opening polymerization of propylene oxide, initiated with protonated phosphazene alkoxides and based on monomer activation with a Lewis acid, is investigated. Alcohols bearing one or several protected hydroxyl groups, namely 1,2-isopropylideneglycerol, 1,2:3,4-di-O-isopropylidene-Dgalactopyranose and poly(propylene glycol), are firstly deprotonated with a phosphazene base. Their combination with triisobutylaluminum enables quantitative and controlled synthesis of poly(propylene oxide) in a very short time (hours), at room temperature and in hydrocarbons. The chain-ends determination showed a main population initiated by the protonated phosphazene alkoxide. A population coming from the residual transfer to monomer is also observed but in very low intensity. Molar masses of 80 000 g mol À1 with relatively narrow dispersity could be prepared. After deprotection of protected hydroxyl functions, tri-and penta-hydroxy telechelic poly(propylene oxide) were obtained. Dihydroxy telechelic polymers of high molar masses are also rapidly and directly synthesized from poly (propylene glycol).

Modification of proline‐based 2,5‐diketopiperazines by anionic ring‐opening polymerization

“…The incorporation of Lewis acid to the reaction mixture has already been used to promote the activated monomer mechanism for the polymerization of oxirane monomers with various initiators . In particular, alcohol/phosphazene base initiating systems combined with i‐Bu 3 Al have been used to synthesize high molar mass poly(propylene oxide) or to polymerize N ‐glycidylphthalimide . These systems strongly increase the rate of polymerization due to the monomer activation and minimize transfer and side reactions thanks to the selective reactivity of the Lewis acid‐anion‐counter‐ion complexes formed as initiating and propagating species.…”

Anionic ring‐opening polymerization of N‐glycidylphthalimide: Combination of phosphazene base and activated monomer mechanism

“…For this purpose, we used a Lewis acid which activates the monomer by increasing its electrophilicity and a phosphazene base resulting in highly nucleophilic propagating centers due to a high degree of ion-pair separation with phosphazenium counterion. 22 In addition, we have also studied the effect of solvent in polymerization, since the solubility of polyglycidylphthalimide is a limiting factor in chain growth. The resulting polymers were fully characterized by NMR, SEC and MALDI-TOF.…”

Dialkylmagnesium‐Promoted Deprotonation of Protic Precursors for the Activated Anionic Ring‐Opening Polymerization of Epoxides

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A family of extremely strong Brönsted bases called phosphazene superbases, [13] was also employed as effective organic catalysts or promoters for the polymerization of various types of monomers, including epoxides. [14][15][16][17][18][19][20][21][22] Due to their high basicity, non-nucleophilic nature, good solubility in a wide range of solvents, and easy handling, phosphazene bases can be readily used to turn protic moieties into nucleophilic initiating sites through deprotonation or activation of weak nucleophiles. Hydroxyl groups were the most commonly employed protic moieties due to their wide variety and high availability.

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