Zheng Yuting, Jiang Shu, Liu Ming, Yu Zhixin, Ma Yanping, Solan Gregory A, Zhang Wenjuan, Liang Tongling, Sun Wen-Hua
School of Pharmaceutical Sciences, Changchun University of Chinese Medicine Changchun 130117 China
Key Laboratory of Engineering Plastics, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences Beijing 100190 China
RSC Adv. 2022 Sep 1;12(37):24037-24049. doi: 10.1039/d2ra04321a. eCollection 2022 Aug 22.
The following family of ,-diaryl-2,3-dimethyl-1,4-diazabutadienes, ArN[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]NAr (Ar = 2,6-Me-4-{CH(4-FCH)}CHL1, 2-Me-6-Et-4-{CH(4-FCH)}CHL2, 2,4-{CH(4-FCH)}-6-MeCHL3, 2,4-{CH(4-FCH)}-6-EtCHL4, 2,4-{CH(4-FCH)}-6-iPrCHL5), each incorporating -substituted 4,4-difluorobenzhydryl groups but differing in the -pairing, have been synthesized and used as precursors to their respective nickel(ii) bromide complexes, Ni1-Ni5. Compound characterization has been achieved through a combination of FT-IR, multinuclear NMR spectroscopy (H, C, F) and elemental analysis. In addition, L1, Ni1 and Ni5 have been structurally characterized with Ni1 and Ni5 revealing similarly distorted tetrahedral geometries about nickel but with distinct differences in the steric protection offered by the -substituents. All nickel complexes, under suitable activation, showed high activity for ethylene polymerization with a predilection towards forming branched high molecular weight polyethylene with narrow dispersity. Notably the most sterically bulky Ni5, under activation with either EtAlCl, EtAlCl or EASC, was exceptionally active (0.9-1.0 × 10 g of PE per (mol of Ni) per h) at an operating temperature of 40 °C. Furthermore, the polyethylene generated displayed molecular weights close to one million g mol ( range: 829-922 kg mol) with high branching densities (86-102/1000 carbons) and a selectivity for short chain branches (% Me = 94.3% (EtAlCl), 87.2% (EtAlCl), 87.7% (EASC)). Further analysis of the mechanical properties of the polymers produced at 40 °C and 50 °C using Ni5 highlighted the key role played by crystallinity ( ) and molecular weight ( ) on tensile strength ( ) and elongation at break ( ). In addition, stress-strain recovery tests reveal these high molecular weight polymers to exhibit characteristics of thermoplastic elastomers (TPEs).
以下一系列的α，α-二芳基-2,3-二甲基-1,4-二氮杂丁二烯，ArN═C(Me)C(Me)═NAr（Ar = 2,6-二甲基-4-{CH(4-氟苄基)}苯基L1、2-甲基-6-乙基-4-{CH(4-氟苄基)}苯基L2、2,4-{CH(4-氟苄基)}-6-甲基苯基L3、2,4-{CH(4-氟苄基)}-6-乙基苯基L4、2,4-{CH(4-氟苄基)}-6-异丙基苯基L5），每个都含有α-取代的4,4-二氟二苯甲基基团，但在α-配对上有所不同，已被合成并用作其各自溴化镍（II）配合物Ni1 - Ni5的前体。通过傅里叶变换红外光谱（FT-IR）、多核核磁共振光谱（氢、碳、氟）和元素分析相结合的方法实现了化合物表征。此外，L1、Ni1和Ni5已进行了结构表征，Ni1和Ni5显示出围绕镍的类似扭曲四面体几何结构，但α-取代基提供的空间保护存在明显差异。所有镍配合物在适当活化下对乙烯聚合表现出高活性，倾向于形成具有窄分散度的支化高分子量聚乙烯。值得注意的是，空间位阻最大的Ni5在使用EtAlCl₂、EtAlCl₃或EASC活化时，在40℃的操作温度下具有极高的活性（每（摩尔镍）每小时0.9 - 1.0×10⁵克聚乙烯）。此外，生成的聚乙烯分子量接近一百万克每摩尔（范围：829 - 922千克每摩尔），具有高支化密度（86 - 102/1000个碳）和对短链支化的选择性（甲基百分比 = 94.3%（EtAlCl₂）、87.2%（EtAlCl₃）、87.7%（EASC））。对使用Ni5在40℃和50℃下生产的聚合物的机械性能进行的进一步分析突出了结晶度（χc）和分子量（Mw）对拉伸强度（σ）和断裂伸长率（εb）所起的关键作用。此外，应力 - 应变恢复测试表明这些高分子量聚合物表现出热塑性弹性体（TPE）的特性。
