Corporate Research and Engineering, Eastman Kodak Company, Rochester, NY 14650-2136, USA.
J Chromatogr A. 2011 Aug 26;1218(34):5801-9. doi: 10.1016/j.chroma.2011.06.078. Epub 2011 Jun 30.
A size-exclusion chromatography (SEC) method in N,N-dimethylformamide containing 0.1 M LiNO(3) is shown to be suitable for the determination of molar mass distributions of three classes of perfluorosulfonated ionomers, including Nafion(®). Autoclaving sample preparation is optimized to prepare molecular solutions free of aggregates, and a solvent exchange method concentrates the autoclaved samples to enable the use of molar-mass-sensitive detection. Calibration curves obtained from light scattering and viscometry detection suggest minor variation in the specific refractive index increment across the molecular size distributions, which introduces inaccuracies in the calculation of local absolute molar masses and intrinsic viscosities. Conformation plots that combine apparent molar masses from light scattering detection with apparent intrinsic viscosities from viscometry detection partially compensate for the variations in refractive index increment. The conformation plots are consistent with compact polymer conformations, and they provide Mark-Houwink-Sakurada constants that can be used to calculate molar mass distributions without molar-mass-sensitive detection. Unperturbed dimensions and characteristic ratios calculated from viscosity-molar mass relationships indicate unusually free rotation of the perfluoroalkane backbones and may suggest limitations to applying two-parameter excluded volume theories for these ionomers.
一种在含有 0.1 M LiNO(3)的 N,N-二甲基甲酰胺中的尺寸排阻色谱（SEC）方法被证明适用于三种全氟磺酸离子聚合物的摩尔质量分布的测定，包括 Nafion(®)。优化了高压釜样品制备方法，以制备无聚集体的分子溶液，并采用溶剂交换方法浓缩高压釜样品，以实现对摩尔质量敏感的检测。来自光散射和粘度检测的校准曲线表明，在分子尺寸分布中特定折光指数增量存在微小变化，这会导致局部绝对摩尔质量和特性粘度计算的不准确性。将光散射检测的表观摩尔质量与粘度检测的表观特性粘度结合起来的构象图部分补偿了折射率增量的变化。构象图与聚合物的紧凑构象一致，并提供了可以用于计算摩尔质量分布而无需摩尔质量敏感检测的马克-豪温克-萨卡里达常数。从粘度-摩尔质量关系计算得到的无扰尺寸和特征比表明全氟烷烃主链的旋转非常自由，这可能表明对于这些离子聚合物应用两参数排除体积理论存在限制。
