Laboratory for Advanced Separations Technologies, Department of Chemistry and Geochemistry, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401-1887, USA.
J Chromatogr A. 2010 Mar 5;1217(10):1667-73. doi: 10.1016/j.chroma.2010.01.035. Epub 2010 Jan 18.
The challenging task of characterizing polydisperse polymer mixtures possessing ultrahigh molecular weight (MW) polymers and microgels in organic solvents is addressed with thermal field-flow fractionation (ThFFF) and multiangle light scattering-differential refractive index (MALS-dRI) detection. In initial experiments, a 350,000 g/mol poly(methyl methacrylate) (PMMA) standard is used to evaluate the effects of temperature gradient and temperature gradient programming on the measurements. dRI baseline fluctuations caused by temperature programming were minimized by using a mobile phase heater to thermostat connecting tubing. ThFFF-MALS-dRI is then used to separate and characterize a complex polyvinyl acetate (PVAc) sample containing ultrahigh MW polymers and microgels. The open channel design employed by ThFFF allowed the PVAc sample to be analyzed with minimal sample preparation. Unfiltered PVAc sample showed components with MWs close to 10(9) g/mol and root mean square radius r(rms) values approaching 400 nm. The same sample, filtered through a 0.5 microm pore-size membrane, yielded a MW that was at least one order of magnitude lower. These results demonstrated that the common practice of prefiltering polymer samples prior to analysis can lead to erroneously low average MWs and polydispersities. The accuracy of MW and r(rms) calculated using standard light scattering equations developed for small scattering molecules and relatively high wavelengths is also examined.
热场流分级（ThFFF）和多角度光散射-差示折射率（MALS-dRI）检测可用于分析具有超高分子量（MW）聚合物和微凝胶的多分散聚合物混合物，这是一项具有挑战性的任务。在初始实验中，使用 350,000 g/mol 的聚甲基丙烯酸甲酯（PMMA）标准来评估温度梯度和温度梯度编程对测量的影响。通过使用流动相加热器对连接管进行恒温来最小化温度编程引起的 dRI 基线波动。然后，使用 ThFFF-MALS-dRI 分离和表征含有超高 MW 聚合物和微凝胶的复杂聚醋酸乙烯酯（PVAc）样品。ThFFF 采用的开放式通道设计允许在最小样品制备的情况下分析 PVAc 样品。未经过滤的 PVAc 样品显示出 MW 接近 10（9）g/mol，均方根半径 r(rms)值接近 400nm。相同的样品，经过 0.5 微米孔径的膜过滤，得到的 MW 至少低一个数量级。这些结果表明，在分析之前对聚合物样品进行预过滤的常见做法可能导致平均 MW 和多分散性错误地降低。还检查了使用针对小散射分子和相对高波长开发的标准光散射方程计算的 MW 和 r(rms)的准确性。
