Nuclear magnetic resonance measurements of molecular weights. Self-diffusion of poly(methyl methacrylate) in acetonitrile
Nuclear magnetic resonance measurements of molecular weights. Self-diffusion of poly(methyl methacrylate) in acetonitrile
复制标题
分子量的核磁共振测量。
DOI：
10.1021/ma00170a019
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
F. Blum
中科院分区：
文献类型：
--
作者：
Ravi Raghavan;T. L. Maver;F. Blum
脉冲梯度自旋回波核磁共振技术已用于研究单分散和多分散聚甲基丙烯酸甲酯（PMMA）在 5 wt% 乙腈-d3 溶液中在 40 C 下的自扩散。单分散 PMMA 甲氧基共振的自旋回波衰减呈指数规律，并由单一自扩散系数 D 表征。自扩散系数随分子量的变化聚合物遵循简单的比例定律，D-2.5 X 10~ e (M)'0'81· 对于多分散PMMA样品，观察到自旋回波强度的非指数衰减。通过使用实验标度定律，多分散聚合物的衰减曲线可用于确定聚合物的分子量。结果发现，分子量分布的简单指数（单分散）、Schulz、组合和歧化模型都给出了重均分子量的合理估计，这与凝胶渗透色谱测量获得的结果一致。然而，各种分子量分布的拟合精度使得重均分子量可能是在这些实验中可以高精度确定的最大分子量。
The pulsed-gradientspin-echo NMR technique has been used to study the self-diffusion of both monodisperse and polydisperse poly (methyl methacrylate)(PMMA) in 5 wt% solutions in acetonitrile-d3 at 40 C. The spin-echo attenuation for the methoxy resonance of monodisperse PMMA is exponential and characterized by a single self-diffusion coefficient, D. The variationin the self-diffusion coefficient with molecular weight of the polymer follows a simple scaling law, with D-2.5 X lO~ e (M)'0'81· For polydisperse PMMA samples nonexponential decays of the spin-echo intensity are observed. By use of the experimental scaling law, the decay curves for thepolydisperse polymers could be used to determine the molecular weight of the polymer. It was found that simple exponential (monodisperse), Schulz, combination, and disproportionation models for molecular weight distributions all gave reasonable estimates of the weight-average molecular weight which were consistent with those obtainedfrom gel permeation chromatography measurements. However, the accuracy of the fits for the various molecular weight distributions is such that a weight-average molecular weight is perhaps the most that can be determined with good accuracyin these experiments.