Lee Young Joo, Bingöl Bahar, Murakhtina Tatiana, Sebastiani Daniel, Meyer Wolfgang H, Wegner Gerhard, Spiess Hans Wolfgang
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
J Phys Chem B. 2007 Aug 23;111(33):9711-21. doi: 10.1021/jp072112j. Epub 2007 Jul 27.
The structure and the local proton mobility of poly(vinyl phosphonic acid) were studied by solid-state NMR under fast magic-angle spinning. At elevated temperatures, the signature of the hydrogen-bonded P-OH protons is observed in 1H magic-angle spinning (MAS) NMR as a single resonance at 10.5 ppm. Both 1H double-quantum NMR and variable-temperature experiments demonstrate that P-OH protons are mobile and thus able to contribute to proton conductivity. Below room temperature, two different types of hydrogen-bonded P-OH resonances are observed at 10.5 and 15 ppm, and 1H double-quantum NMR demonstrates that these protons are immobile on the NMR time scale. By means of first-principles calculations of a model polymer, we have assigned the additional hydrogen-bonded species at lower temperatures to phosphonic acid anhydride and charged anhydride. Also, in the 31P MAS NMR spectrum, two distinct resonances appear, arising from "normal" phosphonic acid and phosphonic acid anhydride. 31P double-quantum NMR experiments reveal that there is no phase segregation between normal and phosphonic acid anhydride and the condensation reaction occurs randomly throughout the system. The formation of acid anhydride leads to a decrease in proton conductivity through two mechanisms, (1) decrease in the number of charge carriers and (2) blockage of charge transport pathways through immobilization of charge carriers together with a hindered reorientation of the anhydride group. Our results provide strong evidence for these mechanisms by demonstrating that the conductivity is greatly influenced by the presence of phosphonic acid anhydride.
通过快速魔角旋转固态核磁共振研究了聚乙烯基膦酸的结构和局部质子迁移率。在高温下，1H 魔角旋转（MAS）核磁共振中观察到氢键合的 P-OH 质子的信号，在 10.5 ppm 处为单一共振峰。1H 双量子核磁共振和变温实验均表明，P-OH 质子具有迁移性，因此能够对质子传导率产生贡献。在室温以下，在 10.5 和 15 ppm 处观察到两种不同类型的氢键合 P-OH 共振峰，1H 双量子核磁共振表明这些质子在核磁共振时间尺度上是不移动的。通过对模型聚合物进行第一性原理计算，我们将低温下额外的氢键合物种归为膦酸酐和带电酐。此外，在 31P MAS 核磁共振谱中，出现了两个不同的共振峰，分别来自“正常”膦酸和膦酸酐。31P 双量子核磁共振实验表明，正常膦酸和膦酸酐之间不存在相分离，缩合反应在整个体系中随机发生。酸酐的形成通过两种机制导致质子传导率降低，（1）电荷载流子数量减少，（2）通过固定电荷载流子以及阻碍酐基团的重新取向来阻断电荷传输途径。我们的结果通过证明传导率受膦酸酐的存在极大影响，为这些机制提供了有力证据。
