Norbornene Monomer Effects and Mechanistic Insights in Binuclear Nickel-Catalyzed Olefin Chain Walking Copolymerizations,ACS Catalysis

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Norbornene Monomer Effects and Mechanistic Insights in Binuclear Nickel-Catalyzed Olefin Chain Walking Copolymerizations
ACS Catalysis ( IF 11.3 ) Pub Date : 2023-09-18 , DOI: 10.1021/acscatal.3c02702
Bingxin Qu _{1,

2} , Yanan Zhao ₃ , Ping Song ₂ , Yanshan Gao ₃ , You-Yun Zhou ₂ , Xiu-Li Sun ₃ , Qiang Fu ₁ , Xiaoshan Ning ₂ , Junfang Li ₃ , Xiaokang Kuang ₂ , Yong Tang _{2,

3}

Affiliation

Chain walking is a unique process in late transition metal-catalyzed ethylene (α-olefin) polymerizations and can be modulated to achieve control over polyolefin branch type, density, topology, branch stereochemistry, and so on, most of which are unattainable without chain walking. Introducing a second monomer could perturb the chain walking process and afford copolymers with unique microstructures. Here, we report the effects of norbornene (NBE) monomer, which is ring strained and cannot undergo chain walking, in binuclear Ni complex-catalyzed ethylene or α-olefin chain walking copolymerization, and have observed significantly reduced molecular weight, promoted chain transfer, suppressed branching, and the appearance of characteristic olefinic end groups versus their respective homopolymerizations. In contrast, the M_w of the NBE copolymers was reduced by 8.6, 9.4, and 16.4 times for ethylene, propylene, and 1-hexene, respectively. The chain transfer was confirmed by significantly increased chains/catalyst numbers in the copolymerizations, by 15.4, 85.1, and 27.1 times versus homopolymerizations, respectively. While various alkyl branches were generated in ethylene and α-olefin homopolymerization, their NBE copolymers showed much reduced branch density and predominant long chain branches. Olefinic end groups also appeared, predominantly norbornyl-linked vinyl (V_N) for ethylene copolymer, alkyl-linked vinyl (V_E), and vinylene for both propylene and 1-hexene copolymers, suggesting β-H elimination/transfer after ethylene enchainment or propylene/1-hexene 2,1-enchainment. The copolymers’ glass transitions could be broadly tuned from 109 to 326 °C with linear relationships against the NBE content and the slopes depending on the monomer type and reaction temperature, indicating a random and uniform distribution of the enchained comonomer. Furthermore, the mechanistic scenarios for the distinctive NBE monomer effects on chain walking, chain growth, and chain transfer were proposed based on DFT studies, confirming the experimental findings.

中文翻译：

双核镍催化烯烃链步行共聚中降冰片烯单体的影响和机理见解

链步行是后过渡金属催化乙烯（α-烯烃）聚合中的一种独特过程，可以通过调节来实现对聚烯烃支链类型、密度、拓扑、支链立体化学等的控制，其中大多数是没有链步行就无法实现的。引入第二种单体可以扰乱链行走过程并提供具有独特微观结构的共聚物。在这里，我们报道了环张力且不能进行链行走的降冰片烯（NBE）单体在双核镍配合物催化的乙烯或α-烯烃链行走共聚中的作用，并观察到显着降低的分子量，促进链转移，抑制支化，以及特征烯属端基的出现与它们各自的均聚。相比之下，M_{乙烯、丙烯和1-己烯的NBE共聚物的w}分别减少了8.6、9.4和16.4倍。共聚中链/催化剂数量显着增加，分别是均聚的 15.4、85.1 和 27.1 倍，证实了链转移。虽然在乙烯和 α-烯烃均聚过程中产生了各种烷基支链，但它们的 NBE 共聚物显示出大大降低的支链密度和主要的长链支链。烯端基也出现，乙烯共聚物主要是降冰片基连接的乙烯基（V _N），烷基连接的乙烯基（V _E)，以及丙烯和 1-己烯共聚物的亚乙烯基，表明乙烯链或丙烯/1-己烯 2,1-链后发生 β-H 消除/转移。共聚物的玻璃化转变温度可在 109 至 326 °C 范围内广泛调节，与 NBE 含量呈线性关系，斜率取决于单体类型和反应温度，表明链状共聚单体的随机且均匀分布。此外，基于 DFT 研究提出了独特的 NBE 单体对链行走、链增长和链转移影响的机制方案，证实了实验结果。

更新日期：2023-09-18

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