State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, China.
Molecules. 2018 Mar 15;23(3):665. doi: 10.3390/molecules23030665.
This work reveals the silyl ketene acetal (SKA)/B(C₆F₅)₃ Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in situ NMR monitored reaction of SKA with B(C₆F₅)₃ indicated the formation of Frustrated Lewis Pairs (FLPs), although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C₆F₅)₃-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C₆F₅)₃-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C₆F₅)₃ is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). Moreover, using this method, we have successfully synthesized well-defined PMMBL--PMBL, PMMBL--PMBL--PMMBL and random copolymers with the predicated molecular weights () and narrow molecular weight distribution (MWD).
这项工作揭示了硅烯酮缩醛（SKA）/B（C₆F₅）₃路易斯对催化的极性丙烯酸单体的室温基团转移聚合（GTP），包括甲基线性甲基丙烯酸酯（MMA），以及可生物再生的环状单体γ-甲基-α-亚甲基-γ-丁内酯（MMBL）和α-亚甲基-γ-丁内酯（MBL）。通过原位 NMR 监测 SKA 与 B（C₆F₅）₃的反应，表明形成了受阻路易斯对（FLP），尽管对于 MMA 聚合反应较慢，但这种 FLP 体系表现出高度活性和对 MMBL 和 MBL 的活的 GTP。详细的研究，包括关键反应中间体的表征、聚合动力学和聚合物结构，导致了聚合机制，其中聚合是通过 SKA 的酯烯醇基团与 B（C₆F₅）₃ 活化单体的乙烯基之间的分子间迈克尔加成引发的，而硅烷基转移到 B（C₆F₅）₃ 活化单体的羰基上，生成单单体加成物种或活性聚合物种；配位的 B（C₆F₅）₃ 释放到进入的单体中，随后在随后的聚合循环中重复进行分子间迈克尔加成。正如实验数据和基质辅助激光解吸/电离飞行时间质谱（MALDI-TOF MS）的链端分析所证实的那样，这种中性 SKA 类似物是聚合的真正活性物质，并在整个过程中保留下来。此外，我们使用这种方法成功地合成了具有预测分子量（）和窄分子量分布（MWD）的 PMMBL-PMBL、PMMBL-PMBL-PMMBL 和无规共聚物。
