Chemical Reactions and Their Kinetics of atactic-Polyacrylonitrile As Revealed by Solid-State 13C NMR
Chemical Reactions and Their Kinetics of atactic-Polyacrylonitrile As Revealed by Solid-State 13C NMR
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DOI：
10.1021/acs.macromol.6b02239
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发表时间：
2017-01-10
期刊：
影响因子：
5.5
通讯作者：
Miyoshi, Toshikazu
中科院分区：
文献类型：
--
作者：
Liu, Xiaoran;Makita, Yuta;Miyoshi, Toshikazu
用各种固体核磁共振技术研究了经220~290℃热处理的C-13标记无规聚丙烯腈(APAN)粉末在空气和真空条件下的分子间和分子内化学反应及其动力学。应用C-13直接极化幻角自旋(DPMAS)以及通过键和通过空间双量子/单量子单核磁共振技术，得出在290℃空气中热处理300min的APAN采用梯形结构，即含有部分交联环和氧化环的六元共轭芳环和多烯组分。相反，在相同条件下真空热处理的APAN热分解为低聚链，这些低聚链主要由烷基链段连接的孤立芳环组成。此外，用C-13交叉极化(CP)和DPMAS光谱研究了化学反应的早期阶段。后者提供了有关化学反应动力学的定量信息。结果表明，氧气下的化学反应是均匀进行的，其活化能(E-a)比真空下(47+/-2kJ/mol)高，为122+/-3kJ/mol。通过比较两种不同条件下APAN的化学结构和反应动力学，对APAN的化学反应机理进行了详细的探讨。
Inter- and intramolecular chemical reactions and their kinetics for C-13-labeled atactic-polyacrylonitrile (aPAN) powder heat-treated at 220-290 degrees C under air and vacuum were investigated by various solid-state nuclear magnetic resonance (ssNMR) techniques. By applying C-13 direct polarization magic angle spinning (DPMAS) as well as through-bond and through space double quantum/single quantum ssNMR techniques, it was concluded that aPAN heat-treated under air at 290 degrees C for 300 min adopted the ladder formation, namely, conjugated six-membered aromatic rings with partially cross-linked and oxidized rings and polyene components. In contrast, aPAN heat-treated under vacuum at the same condition thermally decomposed into oligomeric chains that were mainly composed of isolated aromatic rings connected by alkyl segments. Furthermore, early stages of the chemical reactions were investigated by C-13 cross-polarization (CP) and DPMAS spectra. The latter provided quantitative information regarding the kinetics of the chemical reactions. As a result, it was shown that chemical reactions under oxygen occurred homogeneously with a higher activation energy (E-a) of 122 +/- 3 kJ/mol compared to that of vacuum at 47 +/- 2 kJ/mol. By comparing both chemical structures and kinetics under two different conditions, the chemical reaction mechanisms of aPAN will be discussed in detail.