Laboratoire de Chimie des Polymères Organiques (LCPO) - ENSCPB - CNRS, Université Bordeaux, 16 Av. Pey Berland, 330607 Pessac Cedex 9, France.
J Am Chem Soc. 2009 Mar 11;131(9):3201-9. doi: 10.1021/ja809246f.
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 degrees 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 NuSiMe(3) at the completion of the polymerization, a variety of end-functionalized PEO chains could be generated. In particular, alpha,omega-bis(hydroxy)-telechelic PEO, alpha-benzyl,omega-hydroxy, and alpha-azido,omega-hydroxy-difunctionalized PEOs were synthesized by NHC (1)-initiated ZROP, using H(2)O, PhCH(2)OH, and N(3)SiMe(3) as terminating agent, respectively. Characterization of these alpha,omega-difunctionalized PEOs by techniques such as (1)H NMR spectroscopy, MALDI-TOF spectrometry, and size exclusion chromatography confirmed the quantitative introduction of functional groups at both alpha and omega positions of the PEO chains and the formation of very narrow molar mass polymers. Finally, the synthesis of a poly(ethylene oxide)-b-poly(epsilon-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.
一种 N-杂环卡宾（NHC），即 1,3-双（二异丙基）咪唑-2-亚基（1），被证明可以在 50°C 下在二甲亚砜中引发环氧乙烷的无金属开环聚合，而无需任何其他试剂。因此，可以以定量产率获得具有小于 1.2 的分散度和与 [单体]/[(1)] 比完美匹配的摩尔质量的聚（环氧乙烷）（PEO），证明了这种卡宾引发的聚合具有可控/活性特征。有人认为（1）与环氧乙烷加成形成两性离子物种，即 1,3-双（二异丙基）咪唑-2-亚基氧𬭩盐，然后通过两性离子开环聚合（ZROP）机制进一步聚合。通过在聚合完成时选择适当的终止剂 NuH 或 NuSiMe(3)，可以生成各种端官能化的 PEO 链。特别是，通过 NHC（1）引发的 ZROP，使用 H(2)O、PhCH(2)OH 和 N(3)SiMe(3)作为终止剂，分别合成了α,ω-双（羟基）-遥爪 PEO、α-苄基、ω-羟基和α-叠氮基、ω-羟基-二官能化 PEO。通过（1）H NMR 光谱、MALDI-TOF 光谱和尺寸排阻色谱等技术对这些α,ω-二官能化 PEO 的表征证实了在 PEO 链的α和ω位置定量引入了官能团，并形成了非常窄的摩尔质量聚合物。最后，使用（1）作为有机引发剂，成功地通过相应单体的顺序 ZROP 合成了聚（环氧乙烷）-b-聚（ε-己内酯）嵌段共聚物，而无需分离 PEO 嵌段中间体。
