HRMAS NMR for Studying Solvent-Induced Mobility of Polymer Chains and Metallocene Migration Into Low-Density Polyethylene (LDPE).

IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Magnetic Resonance in Chemistry Pub Date : 2024-11-06 DOI:10.1002/mrc.5484
John C Hoefler, Maxwell R Kimball, Janet Blümel
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Abstract

HRMAS (high-resolution magic angle spinning) nuclear magnetic resonance (NMR) spectroscopy of low-density polyethylene (LDPE) affords 1H and 13C NMR spectra with superior resolution. For acquiring HRMAS NMR spectra, the polymer is first swollen with representative organic solvents. Then, the samples are measured with a conventional solid-state NMR spectrometer in the wideline mode or at the low spinning speed of 2 kHz. Anisotropic interactions like CSA (chemical shift anisotropy) and dipolar interactions are reduced due to the additional mobility of the polymer chains in the presence of the solvent within the polymer network. The combined effect of this mobility and MAS leads to signals with substantially reduced halfwidths as compared to classic MAS of the dry polymer. With HRMAS, all signals of the polymer become visible, and the spectra can be used for a quick and easy assessment of the polymer swelling behavior in diverse solvents. Being able to characterize polymers on the molecular level, and identifying the solvents that penetrate the polymer network best, enables the study of post-synthesis modifications of the polymers. It is demonstrated by paramagnetic HRMAS that the metallocene nickelocene (Cp2Ni) penetrates the LDPE network along with the solvent and is homogeneously dispersed in the polymer. SEM images prove that the structure of the polymer is not altered by the presence of a solvent and Cp2Ni. The impact of the paramagnetic Cp2Ni on the 1H signal halfwidth and T1 time of LDPE is studied. HRMAS allows a quick assessment of metal complexes regarding their ability to penetrate the LDPE network and therefore supports future studies of catalytic polymer degradation.

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HRMAS NMR 用于研究溶剂诱导的聚合物链流动性以及茂金属向低密度聚乙烯 (LDPE) 的迁移。
低密度聚乙烯(LDPE)的 HRMAS(高分辨率魔角旋转)核磁共振(NMR)光谱可提供分辨率极高的 1H 和 13C NMR 光谱。要获取 HRMAS NMR 光谱,首先要用有代表性的有机溶剂溶胀聚合物。然后,使用传统固态 NMR 光谱仪以宽线模式或 2 kHz 的低旋转速度测量样品。由于聚合物网络中存在溶剂,聚合物链具有额外的流动性,因此 CSA(化学位移各向异性)和偶极性等各向异性相互作用会减弱。与干聚合物的传统 MAS 相比,这种流动性和 MAS 的共同作用导致信号的半宽度大大减小。有了 HRMAS,聚合物的所有信号都变得清晰可见,光谱可用于快速、轻松地评估聚合物在不同溶剂中的溶胀行为。能够在分子水平上描述聚合物的特性,并确定最能穿透聚合物网络的溶剂,有助于研究聚合物的合成后改性。顺磁 HRMAS 证明,茂金属二茂镍 (Cp2Ni) 与溶剂一起渗透到 LDPE 网络中,并均匀地分散在聚合物中。扫描电子显微镜图像证明,聚合物的结构不会因溶剂和 Cp2Ni 的存在而改变。研究了顺磁 Cp2Ni 对 LDPE 的 1H 信号半宽和 T1 时间的影响。HRMAS 可以快速评估金属复合物穿透 LDPE 网络的能力,因此有助于今后对催化聚合物降解的研究。
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来源期刊
CiteScore
4.70
自引率
10.00%
发文量
99
审稿时长
1 months
期刊介绍: MRC is devoted to the rapid publication of papers which are concerned with the development of magnetic resonance techniques, or in which the application of such techniques plays a pivotal part. Contributions from scientists working in all areas of NMR, ESR and NQR are invited, and papers describing applications in all branches of chemistry, structural biology and materials chemistry are published. The journal is of particular interest not only to scientists working in academic research, but also those working in commercial organisations who need to keep up-to-date with the latest practical applications of magnetic resonance techniques.
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