The Dow Chemical Company, Analytical Sciences R&D, 1897 Building, Midland, MI 48667, USA.
J Chromatogr A. 2011 Oct 7;1218(40):7173-9. doi: 10.1016/j.chroma.2011.08.036. Epub 2011 Aug 17.
The application of high temperature comprehensive two-dimensional (2D) liquid chromatography for quantitative characterization of chemical composition and molecular weight (MW) heterogeneities in polyolefins is demonstrated in this study by separating a physical blend of isotactic-polypropylene, ethylene-random-propylene copolymer, and high density polyethylene. The first dimension separation is based on adsorption liquid chromatography that fractionates the blend from low to high ethylene content. The second dimension is size-exclusion chromatography connected with light scattering (LS) and infrared (IR) detectors. The IR detector shows desired sensitivity and linearity for monitoring analyte concentrations in the eluent after 2D separations. In addition, the compositions of the analytes are also determined from the ratio of two IR absorbances at the specified wavelength regions, an absorbance for measuring the level of methyl groups in polyolefins and another absorbance for measuring concentration. The LS detector is used to determine absolute molecular weight of the analytes from the ratio of the light scattering signal to the IR concentration signal. The ability to obtain concentration, chemical composition, and MW of polyolefins after 2D separation provides new opportunities to discover structure-property relationships for polyolefins with complex structures/architectures.
本研究通过分离等规聚丙烯、乙烯随机丙烯共聚物和高密度聚乙烯的物理混合物，展示了高温综合二维（2D）液相色谱法在定量表征聚烯烃化学成分和分子量（MW）异质性方面的应用。一维分离基于吸附液相色谱，可将混合物从低到高的乙烯含量进行分级。二维为尺寸排阻色谱法，与光散射（LS）和红外（IR）检测器相连。IR 检测器在 2D 分离后监测洗脱液中分析物浓度时具有所需的灵敏度和线性度。此外，还可以从指定波长区域的两个 IR 吸光度比、测量聚烯烃中甲基水平的吸光度和测量浓度的另一个吸光度来确定分析物的组成。LS 检测器用于通过光散射信号与 IR 浓度信号的比值来确定分析物的绝对分子量。在 2D 分离后获得聚烯烃的浓度、化学成分和 MW 的能力为具有复杂结构/架构的聚烯烃发现结构-性能关系提供了新的机会。
