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
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
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DOI：
10.1038/s41428-020-0384-z
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发表时间：
2020-07-22
期刊：
影响因子：
2.8
通讯作者：
Higuchi, Masahiro
中科院分区：
文献类型：
--
作者：
Muramatsu, Yuki;Oga, Yosuke;Higuchi, Masahiro
发现杂环卡宾1，3-二叔丁基咪唑-2-亚甲基(NHCtBu)及其与山梨酸甲酯(MS)的1：1加合物在-20℃的有机溶剂中引发n-取代马来酰亚胺(RMI)的阴离子聚合，分别得到线型和环型聚合物(RMI)S。以甲基双(2，6-二叔丁基-4-甲基苯氧基)铝(MAD)等体积较大的铝路易斯酸(MAD)为添加剂时，观察到了单体的定量消耗。在NHCtBu：MS加合物作为引发剂的存在下，单体消耗之后不需要高度稀释的条件就可以得到含有α-末端MS单元的环状聚(RMI)S，其ANM(N)为3.4×10(3)-6.2×10(3)和宽的多分散指数(M-w/M-n=2.4(3)-2.6(5))。不需要稀释，因为存在α-末端的NHCtBu基团，它在聚合过程中充当传播中心的反阳离子。得到的聚合物的大分子量分布归因于RMI的α-羰基质子的链转移，特别是对邻近的NHCtBu阳离子单元的链转移。H-1NMR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诱导的。用透射电子显微镜直接观察了线型和环型聚合物S的拓扑结构。
TheN-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 ofN-substituted maleimides (RMIs) in organic solvents at -20 degrees 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 alpha-terminal MS units, which exhibited anM(n)of 3.4 x 10(3)-6.2 x 10(3)and a broad polydispersity index (M-w/M-n = 2.4(3)-2.6(5)). Dilution was not required due to the presence of an alpha-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 alpha-carbonyl proton of the RMIs, particularly to the neighboring NHCtBu cation unit.H-1 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).