Details

Autor(en) / Beteiligte

• Raynaud, Jean
• Absalon, Christelle
• Gnanou, Yves
• Taton, Daniel

Titel

N-Heterocyclic Carbene-Induced Zwitterionic Ring-Opening Polymerization of Ethylene Oxide and Direct Synthesis of α,ω-Difunctionalized Poly(ethylene oxide)s and Poly(ethylene oxide)-b-poly(ε-caprolactone) Block Copolymers

Ist Teil von

• Journal of the American Chemical Society, 2009-03, Vol.131 (9), p.3201-3209

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2009

Quelle

MEDLINE

Beschreibungen/Notizen

• An N-heterocyclic carbene (NHC), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1), was demonstrated to bring about the metal-free ring-opening polymerization of ethylene oxide at 50 °C in dimethyl sulfoxide, in absence of any other reagents. Poly(ethylene oxide) (PEO) of polydispersities <1.2 and molar masses perfectly matching the [monomer]/[(1)] ratio could thus be obtained in quantitative yields, attesting to the controlled/living character of such carbene-initiated polymerizations. It is argued that (1) adds to ethylene oxide to form a zwitterionic species, namely 1,3-bis-(diisopropyl)imidazol-2-ylidinium alkoxide, that further propagates by a zwitterionic ring-opening polymerization (ZROP) mechanism. Through an appropriate choice of terminating agent NuH or NuSiMe3 at the completion of the polymerization, a variety of end-functionalized PEO chains could be generated. In particular, α,ω-bis(hydroxy)-telechelic PEO, α-benzyl,ω-hydroxy, and α-azido,ω-hydroxy-difunctionalized PEOs were synthesized by NHC (1)-initiated ZROP, using H2O, PhCH2OH, and N3SiMe3 as terminating agent, respectively. Characterization of these α,ω-difunctionalized PEOs by techniques such as 1H NMR spectroscopy, MALDI-TOF spectrometry, and size exclusion chromatography confirmed the quantitative introduction of functional groups at both α and ω positions of the PEO chains and the formation of very narrow molar mass polymers. Finally, the synthesis of a poly(ethylene oxide)-b-poly(ε-caprolactone) diblock copolymer by sequential ZROP of the corresponding monomers was successfully achieved using (1) as organic initiator without isolation of the PEO block intermediate.