Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
J Am Chem Soc. 2021 Nov 17;143(45):18832-18837. doi: 10.1021/jacs.1c08512. Epub 2021 Nov 5.
Polyethylene-poly(methyl acrylate) multiblock copolymers were obtained using a catalyst system consisting of a pentamethylcyclopentadienyl cobalt complex (Co(η-CH)P(OMe)I) and -butyl modified methylaluminoxane (MMAO). As the chain-growth mechanism, the self-switching between organometallic-mediated radical polymerization (OMRP) and coordination-insertion polymerization (CIP) is suggested. As a possible polymerization mechanism, we propose that (1) the methyl and -butyl groups transfer from Al to Co and the single methyl acrylate (MA) unit insertion into the Me-Co and H-Co allows for the formation of Co-C(COOMe) bonds as an initiator for OMRP of MA, (2) the migratory insertion of ethylene into Co-C(COOMe) bonds leads to the formation of an alkyl-Co species as active species for CIP of ethylene, and (3) MA insertion to the alkyl-Co to regenerate a Co-C(COOMe) bond. The architectures of copolymers were confirmed by various nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), and size-exclusion chromatography (SEC) analyses.
采用由五甲基环戊二烯基钴配合物（Co(η-CH)P(OMe)I）和 - 丁基改性甲基铝氧烷（MMAO）组成的催化剂体系，得到了聚乙烯-聚（甲基丙烯酸甲酯）多嵌段共聚物。作为链增长机制，建议在有机金属介导的自由基聚合（OMRP）和配位插入聚合（CIP）之间进行自切换。作为一种可能的聚合机理，我们提出（1）甲基和 - 丁基从 Al 转移到 Co，并且单体甲基丙烯酸甲酯（MA）单元插入 Me-Co 和 H-Co 中，允许形成 Co-C（COOMe）键，作为 MA 的 OMRP 的引发剂，（2）乙烯向 Co-C（COOMe）键的迁移插入导致形成烷基-Co 物种，作为乙烯 CIP 的活性物种，和（3）MA 插入到烷基-Co 中以重新生成 Co-C（COOMe）键。共聚物的结构通过各种核磁共振（NMR）、热重分析（TGA）/差示扫描量热法（DSC）和尺寸排阻色谱（SEC）分析得到证实。
