Structural Analysis of the End Groups and Substructures of Commercial Poly(ethylene terephthalate) by Multiple-WET 1H/13C NMR
Structural Analysis of the End Groups and Substructures of Commercial Poly(ethylene terephthalate) by Multiple-WET 1H/13C NMR
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DOI：
10.1021/acs.macromol.6b01105
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发表时间：
2016-07
期刊：
影响因子：
5.5
通讯作者：
Kimiko Tanaka;Muneki Oouchi;Fumiaki Hayashi;H. Maeda;H. Waki
中科院分区：
文献类型：
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作者：
Kimiko Tanaka;Muneki Oouchi;Fumiaki Hayashi;H. Maeda;H. Waki
核磁共振（NMR）无疑已成为聚合物结构和动力学研究中最有价值的光谱技术之一。在最近的一篇综述文章中，de Ilarduya和Mun Mundoz-Guerra很好地强调了NMR在聚酯结构研究中的应用。1然而，通过溶液1H NMR对商业聚对苯二甲酸乙二醇酯（PET）的端基进行结构表征一直具有挑战性，因为灵敏度差，主成分和溶剂信号严重重叠，以及NMR仪器的动态范围不足。通常，低分子量模型化合物2、3和/或13C标记实验4用于分配NMR信号。微观结构，商业PET的乙烯基端基除外，其特征在于使用溶液NMR和模型NMR。[2]在Amari等人随后的研究中，来自乙烯基端基的三个质子信号中的一个被乙二醇（EG）单元的主信号掩蔽，并且在PET溶液的1H NMR光谱中仅识别出三个质子信号中的两个。因此，开发一种抑制源自主要组分（对苯二甲酸乙二醇酯（EG-TA））和溶剂（CDCl3、C5D5N和HFIP-d2）的强1H信号的方法对于观察来自所有端基的NMR信号至关重要。因此，可以在不使用任何模型化合物和/或13C标记实验的情况下完成端基信号的分配。之前，通过T1效应（WET）6 − 9增强的水抑制与二维双量子相干相结合，以抑制来自聚醚砜主要组分的两个信号和来自溶剂的一个信号; 10出于类似目的，双预饱和1H NMR用于聚乙烯的不饱和表征。11在这项研究中，我们展示了在多维（2D和3D）1H和13C化学位移相关实验12中使用多重WET-NMR方法来消除这些强信号。结果，我们观察到来自端基的1H信号，如乙烯基、甲酯等，这是一种具有出色灵敏度的商用PET，因此为这些端基的完全分配铺平了道路，如本研究所示（图1）。使用1D 13C NMR方法精确测量13C化学位移，以确认来自2D和3D相关数据的归属。此外，多个WET序列与反转恢复脉冲序列相结合，以获得1H自旋晶格弛豫时间，最终研究PET中端基和子结构的动力学。
Nuclear magnetic resonance (NMR) has undoubtedly emerged as one of the most valuable spectroscopic techniques for structural and dynamics studies of polymers. In a recent review article, de Ilarduya and Muñoz-Guerra well highlight the application of NMR to the structural study of polyesters. 1 However, the structural characterization of the end groups of commercial poly (ethylene terephthalate)(PET) by solution 1H NMR has always been challenging because of poor sensitivity, severe overlaps of the main-component and solvent signals, and the insufficient dynamic range of NMR instruments. In general, low-molecular-weight model compounds 2, 3 and/or 13C-labeling experiments 4 are used to assign the NMR signals. Microstructures barring the vinyl end group of commercial PET were characterized using solution NMR and a model copolyester. 2 In a subsequent study by Amari et al., 5 one of the three proton signals from the vinyl end group was masked by the main signal of the ethylene glycol (EG) unit, and only two of the three proton signals were identified in the 1H NMR spectrum of a PET solution. Therefore, the development of a method to suppress strong 1H signals originating from the main components (ethylene terephthalate (EG-TA)) and solvents (CDCl3, C5D5N, and HFIP-d2) is essential to observing the NMR signals from all of the end groups. Hence, the assignment of the end group signals can be accomplished without using any model compounds and/or 13C-labeling experiments. Previously, water suppression enhanced through T1 effects (WET) 6− 9 was combined with 2D double-quantum coherence to suppress two signals from the main component of poly (ether sulfone) and one signal from the solvent; 10 for a similar purpose, double presaturation 1H NMR was used for the unsaturation characterization of polyethylene. 11 In this study, we demonstrate the use of a multiple WET-NMR method implemented in multidimensional (2D and 3D) 1H and 13C chemical-shift correlation experiments 12 at ultrahigh field (21.1 T) to eliminate these strong signals. As a result, we observed 1H signals from the end groups, such as vinyl, methyl ester, etc., of commercial PET with an excellent sensitivity, hence paving a path to the complete assignment of these end groups, as presented in this study (Figure 1). 13C chemical shifts were accurately measured using a 1D 13C NMR method to confirm the assignments from the 2D and 3D correlation data. In addition, multiple WET sequences were combined with the inversion recovery pulse sequence to obtain 1H spin− lattice relaxation times, ultimately to investigate the dynamics of the end groups and substructures in PET.