The N-heterocyclic carbene 1,3-di-tert-butylimidazol-2-ylidene (NHCtBu) and its 1:1 adduct with methyl sorbate (MS) were found to initiate anionic polymerization of N-substituted maleimides (RMIs) in organic solvents at −20 °C to afford linear and cyclic poly(RMI)s, respectively. Quantitative monomer consumption was observed when a bulky aluminum Lewis acid, such as methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD), was used as an additive. In the presence of the NHCtBu:MS adduct as an initiator, monomer consumption was followed by ring closure without the need for highly diluted conditions to give cyclic poly(RMI)s containing α-terminal MS units, which exhibited an Mn of 3.4 × 103–6.2 × 103 and a broad polydispersity index (Mw/Mn = 2.43–2.65). Dilution was not required due to the presence of an α-terminal NHCtBu group, which acted as a counter cation for the propagating center during polymerization. The broad molecular weight distributions of the obtained polymers were ascribed to a chain transfer upon abstraction of the α-carbonyl proton of the RMIs, particularly to the neighboring NHCtBu cation unit. 1H NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass analyses indicated that the proton transfer of the acidic proton was induced by the propagating anion. The topologies of the linear and cyclic poly(RMI)s were directly observed by transmission electron microscopy (TEM). Direct Observation of Cyclic Poly(N-substituted maleimide)s with Broad Size Distributions Synthesized by Anionic Polymerization using an N-Heterocyclic Carbene and Successive Ring Closure Without High Dilutions.

中文翻译：

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使用 N-杂环卡宾和连续闭环通过阴离子聚合合成的具有宽尺寸分布的环状聚（N-取代马来酰亚胺）的直接观察，无需高稀释

发现 N-杂环卡宾 1,3-二叔丁基咪唑-2-亚基 (NHCtBu) 及其与山梨酸甲酯 (MS) 的 1:1 加合物在有机溶剂中引发 N-取代马来酰亚胺 (RMI) 的阴离子聚合在-20°C 下分别提供线性和环状聚（RMI）。当使用体积大的路易斯酸铝（例如甲基铝双（2,6-二-叔丁基-4-甲基苯醚）（MAD）作为添加剂时，会观察到定量的单体消耗）。在 NHCtBu:MS 加合物作为引发剂的存在下，单体消耗后发生闭环，无需高度稀释的条件即可得到含有 α-末端 MS 单元的环状聚 (RMI)，其 Mn 为 3.4 × 103 –6.2 × 103 和广泛的多分散指数 (Mw/Mn = 2.43–2.65)。由于 α-末端 NHCtBu 基团的存在，不需要稀释，在聚合过程中作为增长中心的抗衡阳离子。所得聚合物的宽分子量分布归因于在提取 RMI 的 α-羰基质子时的链转移，特别是与相邻的 NHCtBu 阳离子单元。1H NMR 和基质辅助激光解吸/电离飞行时间 (MALDI-TOF) 质量分析表明，酸性质子的质子转移是由传播的阴离子引起的。通过透射电子显微镜（TEM）直接观察线性和环状聚（RMI）的拓扑结构。通过使用 N-杂环卡宾和连续闭环的阴离子聚合合成的具有宽尺寸分布的环状聚（N-取代马来酰亚胺）的直接观察，无需高稀释。