Phosphazene-Promoted Metal-Free Ring-Opening Polymerization of Ethylene Oxide Initiated by Carboxylic Acid

Abstract

The effectiveness of carboxylic acid as initiator for the anionic ring-opening polymerization of ethylene oxide was investigated with a strong phosphazene base (t-BuP 4 ) used as promoter. Kinetic study showed an induction period, i.e., transformation of carboxylic acid to hydroxyl ester, followed by slow chain growth together with simultaneous and fast end-group transesterification, which led to poly(ethylene oxide) (PEO) consisting of monoester (monohydroxyl), diester, and dihydroxyl species. An appropriate t-BuP 4 /acid ratio was proven to be essential to achieve better control over the polymerization and low dispersity of PEO. This work provides important information and enriches the toolbox for macromolecular and biomolecular engineering with protic initiating sites.

Polymerization of 5-alkyl δ-lactones catalyzed by diphenyl phosphate and their sequential organocatalytic polymerization with monosubstituted epoxides

“…drug delivery and controlled release, gene therapy, tissue engineering, etc, owing to the combination, complementation and interplay of the respective physicochemical properties such as biodegradability, biocompatibility, solubility/miscibility, rigidity/flexibility, crystallinity derived from each of the blocky components. For example, a strong phosphazene base (t-BuP 4 ) is well suited for the ROP of epoxides (either ethylene oxide or the monosubstituted ones), [17][18][19][20][21][22][23][24][25] while strong organic acids (such as trifluoromethanesulfonic acid, sulfonimide derivatives and phosphoric acids) appear more appropriate for cyclic esters. One-pot sequential ROP of the corresponding epoxide and cyclic ester is clearly the most ideal route for the synthesis of the polyetherpolyester block copolymer, which seems straightforward and facile at the first glance as the polyether and polyester chains both grow maintaining an alkoxide/hydroxyl end group.…”

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

“…Bulky and strong organic bases, called aminophosphazenes, were used as deprotonating agents of alcohols to obtain higher polymerization rates of epoxides [19][20][21]. t-BuP 4 was the most used base for this purpose [22][23][24][25][26][27]. Polymerization systems based on monomer activation developed first by Inoue on propylene oxide were shown to strongly increase the polymerization rates [28,29].…”

Selective Ring‐Opening Polymerization of Non‐Strained γ‐Butyrolactone Catalyzed by A Cyclic Trimeric Phosphazene Base

“…[10] In marked contrast, the tetrameric 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino) phosphoranylidenamino]-2L, 5 4L 5 -catenadi(phosphazene) (tBu-P 4 ,p K a of 42.6 in CH 3 CN) is one of the strongest neutral bases and is extremely active for ROP of both cyclic esters and epoxides. [12] Among all the aliphatic polyesters,w ea re particularly interested in poly(g-butyrolactone) (PgBL) from ROPo fgbutyrolactone (g-BL), which is an aturally renewable monomer derived from succinic acid and ranked as atop biomassderived compound. [12] Among all the aliphatic polyesters,w ea re particularly interested in poly(g-butyrolactone) (PgBL) from ROPo fgbutyrolactone (g-BL), which is an aturally renewable monomer derived from succinic acid and ranked as atop biomassderived compound.…”