The Effect of Trifluoroacetic Acid on Molecular Weight Determination of Polyesters: An in Situ NMR Investigation
The Effect of Trifluoroacetic Acid on Molecular Weight Determination of Polyesters: An in Situ NMR Investigation
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三氟乙酸对聚酯分子量测定的影响：原位 NMR 研究
DOI：
10.1007/s10118-021-2605-0
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发表时间：
2021-07
影响因子：
4.3
通讯作者：
Tu Ying-Feng
中科院分区：
文献类型：
--
作者：
Tu Yan-Yan;Wan Xue-Ting;Huan Jie;Zhu Xiang;Li Xiao-Hong;Tu Ying-Feng
由于芳香族聚酯在普通有机溶剂中的溶解性差，通常使用三氟乙酸作为助溶剂来增加其溶解性以进行表征。然而，只有少数的研究报告，它所引起的副反应，我们在这里介绍的应用在原位1H-NMR技术，探讨其对羟基的端基，这通常是用于聚酯的分子量的端基估计法测定。以对苯二甲酸二（2-羟乙基）酯（BHET）为模型化合物，在三氟乙酸/三氯甲烷（1：10，V：V）混合溶剂中，1H NMR定量结果表明，羟乙基端基的峰积分随时间的延长呈准一级动力学衰减。这是由于羟乙基基团与三氟乙酸的酯化反应，通过1H-13 C梯度增强的杂原子多重键相关（gHMBC）光谱揭示。以对苯二甲酸二甲酯和BHET的不同摩尔比混合物代表不同聚合度的聚对苯二甲酸乙二酯（PET），研究了三氟乙酸对聚酯羟乙基基团估算及分子量测定的影响。我们的结果表明，如果允许5%的相对误差，则NMR测量必须在25 °C下在混合溶剂中制备溶液的1.3 h内完成。结果在PET样品中得到了证实，而在聚己二酸乙二酯中，得到的增粘常数比在芳香体系中的增粘常数快。所得结果可应用于其它含醇官能团的聚合物体系，并可作为端基估计法表征聚酯和聚醚的指导。
Due to the poor solubility of aromatic polyesters in common organic solvents, trifluoroacetic acid is usually used as a co-solvent to increase their solubility for characterizations. However, only few studies have reported the side reactions induced by it. We present here the application of in situ1H-NMR techniques to explore its effect on the hydroxyl end-groups, which are usually used for the molecular weight determination of polyesters by end-group estimation method. Using bis(2-hydroxyethyl) terephthalate (BHET) as model compound, 1H quantitative NMR results show the peak integration of hydroxyethyl end-groups decreased with time via a pseudo-first-order kinetics in dtrifluoroacetic acid/d-chloroform mixture solvent (1:10, V:V). This is due to the esterification of hydroxyethyl groups with trifluoroacetic acid, revealed by the 1H-13C gradient-enhanced heteronuclear multiple bond correlation (gHMBC) spectrum. The mixtures of dimethyl terephthalate and BHET with different molar ratios were used to represent poly(ethylene terephthalate) (PET) with different degrees of polymerization, and the effect of trifluoroacetic acid on the estimation of hydroxyethyl groups and subsequent molecular weight determination of polyesters was studied. Our results show that if a relative error of 5% is allowed, the NMR measurements must be finished within 1.3 h of solution preparation at 25 °C in the mixture solvent. The results were confirmed in PET sample, while in poly(ethylene adipate), the obtained esterifaction constant is faster that those in aromatic system. The results can be applied to other polymer systems with alcohol functionalized groups, and used as a guideline for the characterization of polyesters and polyethers by end-group estimation method.
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DOI：
10.1039/c39790000905
发表时间：
1979
期刊：
Journal of The Chemical Society, Chemical Communications
影响因子：
--
作者：
P. Kavanagh;A. C. Knipe;W. Watts
通讯作者：
P. Kavanagh;A. C. Knipe;W. Watts
影响因子：
5.1
作者：
N. B. Sanches;M. Dias;E. B. Pacheco
通讯作者：
N. B. Sanches;M. Dias;E. B. Pacheco
影响因子：
5.5
作者：
Kimiko Tanaka;Muneki Oouchi;Fumiaki Hayashi;H. Maeda;H. Waki
通讯作者：
Kimiko Tanaka;Muneki Oouchi;Fumiaki Hayashi;H. Maeda;H. Waki
影响因子：
4.1
作者：
Jadhav, Amarsinh L.;Malkar, Radhika S.;Yadav, Ganapati D.
通讯作者：
Yadav, Ganapati D.
影响因子：
4.6
作者：
Sumod Kalakkunnath;D. S. Kalika
通讯作者：
Sumod Kalakkunnath;D. S. Kalika