Center for Education and Research on Macromolecules, Chemistry Department, University of Liège, Belgium.
Chemistry. 2012 Oct 1;18(40):12834-44. doi: 10.1002/chem.201201456. Epub 2012 Aug 21.
This work reveals the preponderance of an intramolecular metal chelation phenomenon in a controlled radical polymerization system involving the reversible trapping of the radical chains by a cobalt complex bis(acetylacetonato)cobalt(II). The cobalt-mediated radical polymerization (CMRP) of a series of N-vinyl amides was considered with the aim of studying the effect of the cobalt chelation by the amide moiety of the last monomer unit of the chain. The latter reinforces the cobalt-polymer bond in the order N-vinylpyrrolidone<N-vinyl caprolactam<N-methyl-N-vinyl acetamide, and is responsible for the optimal control of the polymerizations observed for the last two monomers. Such a double linkage between the controlling agent and the polymer, through a covalent bond and a dative bond, is unique in the field of controlled radical polymerization and represents a powerful opportunity to fine tune the equilibrium between latent and free radicals. Possible hydrogen bond formation is also taken into account in the case of N-vinyl acetamide and N-vinyl formamide. These results are essential for understanding the factors influencing Co-C bond strength in general, and the CMRP mechanism in particular, but also for developing a powerful platform for the synthesis of new precision poly(N-vinyl amide) materials, which are an important class of polymers that sustain numerous applications today.
这项工作揭示了在涉及自由基链通过钴配合物双（乙酰丙酮）钴（II）可逆捕获的可控自由基聚合体系中存在的分子内金属螯合现象的优势。考虑了一系列 N-乙烯基酰胺的钴介导自由基聚合（CMRP），目的是研究最后单体单元的酰胺部分对钴螯合的影响链。后者通过共价键和配位键增强了聚合物与钴之间的键合，其顺序为 N-乙烯基吡咯烷酮<N-乙烯基己内酰胺<N-甲基-N-乙烯基乙酰胺，并负责对最后两种单体观察到的聚合进行最佳控制。在可控自由基聚合领域，这种控制剂和聚合物之间的双链接，通过共价键和配位键，是独一无二的，代表了微调潜在自由基和自由基之间平衡的有力机会。在 N-乙烯基乙酰胺和 N-乙烯基甲酰胺的情况下，还考虑了可能的氢键形成。这些结果对于理解影响 Co-C 键强度的因素很重要，特别是对于 CMRP 机制，也对于开发用于合成新型精密聚（N-乙烯基酰胺）材料的强大平台很重要，这些材料是当今许多应用所依赖的一类重要聚合物。
