Efficient Synthesis of Low-Polydispersity UHMWPE by Elevating Active Sites on Anchored POSS Molecules
Efficient Synthesis of Low-Polydispersity UHMWPE by Elevating Active Sites on Anchored POSS Molecules
复制标题
通过提升锚定 POSS 分子上的活性位点有效合成低多分散性 UHMWPE
DOI：
10.1021/acs.iecr.0c04097
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发表时间：
2020-11-11
影响因子：
4.2
通讯作者：
Li, Wei
中科院分区：
文献类型：
--
作者：
Liang, Peng;Chen, Yuming;Li, Wei
超高分子量聚乙烯（UHMWPE）具有低的多分散性，具有优异的物理机械性能。本论文采用多面体低聚倍半硅氧烷（POSS）改性的Ziegler-Natta催化剂合成了窄分子量分布的超高分子量聚乙烯（UHMWPE）。采用漫反射红外光谱结合CO作为分子探针，X射线光电子能谱和漫反射紫外可见光谱，在研究分子振动和电子性质的基础上，跟踪催化剂结构的演变。结果表明，化学接枝POSS分子在分子水平上均匀分布在二氧化硅表面。POSS可以通过与残留的硅醇质子化来捕获MgTi化合物，作为活性中心的垂直支撑。与直接接枝或吸附在二氧化硅表面上的活性位点相比，接枝在POSS上的所得活性位点呈现出强得多的刘易斯酸性，并且不太均匀（仅四配位Mg 2+物种）。活性位点的这种较小的异质性使得能够合成具有窄得多的分布的UHMWPE，将分子量分布从6.7降低到3.9。
Ultrahigh-molecular-weight polyethylene (UHMWPE) with a low polydispersity exhibits excellently physical and mechanical properties. In this work, a polyhedral oligomeric silsesquioxane (POSS)-modified Ziegler-Natta catalyst has been explored to synthesize the UHMWPE with a narrow molecular weight distribution. Diffuse reflection infrared spectroscopy combined with CO as the molecular probe, X-ray photoelectron spectroscopy, and diffuse reflectance UV-vis spectroscopy are employed to trace the evolution of the catalyst structure based on the investigation of vibrational and electronic properties of molecules. The results demonstrate that the chemically grafted POSS molecules are distributed evenly on the silica surface at the molecular level. The POSS can capture the MgTi compounds through protonation with the residual silanols, acting as a vertical support for active sites. The resulting active sites grafted on the POSS present much stronger Lewis acidity and were less heterogeneous (only tetra-coordinated Mg2+ species) in comparison to the active sites directly grafted or absorbed on the silica surface. This less heterogeneity of active sites enables to synthesize the UHMWPE with a much narrow distribution, reducing the molecular weight distribution from 6.7 to 3.9.