Distribution of correlation times in glassy polymers from pulsed deuteron NMR
Distribution of correlation times in glassy polymers from pulsed deuteron NMR
复制标题
脉冲氘核 NMR 中玻璃态聚合物相关时间的分布
DOI：
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
H. Spiess
中科院分区：
文献类型：
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作者：
C. Schmidt;K. Kuhn;H. Spiess
脉冲氚核磁共振为测定玻璃态聚合物中局部运动的关联时间分布提供了新的可能性。核磁共振线形是对应于不同相关时间值的谱的叠加。这些单一光谱的加权因子取决于分布函数，因此可以用线形分析来表征。此外，与单纯的线形分析相比，结合自旋-晶格弛豫实验可以在更长的时间尺度上探索运动行为。通过这种方式，可以清楚地区分同质分布和异质分布。对该方法进行了详细的解释，并通过一个涉及玻璃态聚碳酸酯中甲基团旋转的简单例子进行了演示。无论是在聚碳酸酯本身还是在含有低分子质量添加剂的混合物中，结果都可以用关联时间的对数-高斯分布来描述。这种分布在本质上是不均匀的，可能是由于活化能在15到21kJ/摩尔之间的空间不同位置的分布所致。
Pulsed deuteron NMR offers new possibilities for the determination of the distribution of correlation times for local motions in glassy polymers. The NMR line shape is a superposition of spectra corresponding to the different values of the correlation times. The weighting factors of these single spectra depend on the distribution function, which therefore can be characterized by a line shape analysis. Moreover, by combination with spin-lattice relaxation experiments the motional behaviour can be probed on a much longer time scale then by a line shape analysis alone. In this way homogeneous and heterogeneous distributions can clearly be distinguished. The method is explained in detail and is demonstrated by a simple example involving the methyl group rotation in glassy polycarbonate. in both polycarbonate itself and in mixtures with low molecular mass additives the results can be described by a log-Gausian distribution of correlation times. This distribution is heterogeneous in nature, probably resulting from a distribution of the activation energies at spatially different sites between 15 and 21 kJ/mole.