Department of Chemistry and Polymer Science, University of Stellenbosch, PO Box X1, 7602, Stellenbosch, South Africa.
Department of Chemistry and Polymer Science, University of Stellenbosch, PO Box X1, 7602, Stellenbosch, South Africa.
Anal Chim Acta. 2021 Feb 1;1144:150-157. doi: 10.1016/j.aca.2020.12.017. Epub 2020 Dec 11.
Size exclusion chromatography is the method of choice for the molar mass analysis of polymers, however, it is not selective towards polymer microstructure. Counterintuitively, asymmetric flow field-flow fractionation (AF4), a channel-based molar mass analysis technique, has been shown to be able to fractionate poly(methyl methacrylate (PMMA) according to tacticity. This was revealed by investigating the solution behaviour of syndiotactic- (s-PMMA), atactic- (a-PMMA) and isotactic (i-PMMA) poly(methyl methacrylate) of similar molecular masses in solvents with different thermodynamic properties. In addition to developing a selective fractionation method, the effects of solvent quality and channel temperature on the fractionation were investigated. It was concluded that the thermodynamic quality of the carrier liquid has a significant influence on the retention behaviour of polymers in AF4. It was shown that the separation of s-PMMA and i-PMMA can be improved by using a theta solvent (acetonitrile) as the carrier liquid instead of thermodynamically good solvents such as tetrahydrofuran and chloroform. In addition, it was found that by using a non-stereocomplexing solvent for PMMA, such as chloroform, blends of s-PMMA and i-PMMA can be separated. Lastly, it was established that the AF4 channel temperature has an influence on the retention behaviour of the PMMA samples. For THF as carrier liquid it was found that the maximum difference in retention between s-PMMA and i-PMMA can be achieved at a channel temperature of 35 °C. In the case of ACN being the carrier liquid, it was observed that the retention behaviour of i-PMMA was significantly more influenced by a change in temperature as compared to s-PMMA and a-PMMA.
体积排阻色谱是聚合物摩尔质量分析的首选方法，但它对聚合物的微观结构没有选择性。反直觉的是，基于通道的摩尔质量分析技术——不对称流场分级（AF4）已被证明能够根据立构规整度对聚甲基丙烯酸甲酯（PMMA）进行分级。这是通过研究具有相似分子量的间规-（s-PMMA）、无规-（a-PMMA）和全同立构-（i-PMMA）聚甲基丙烯酸甲酯在具有不同热力学性质的溶剂中的溶液行为来揭示的。除了开发一种选择性的分级方法外，还研究了溶剂质量和通道温度对分级的影响。结果表明，载体液的热力学质量对 AF4 中聚合物的保留行为有显著影响。结果表明，使用θ溶剂（乙腈）作为载体液而不是热力学良好的溶剂（如四氢呋喃和氯仿）可以改善 s-PMMA 和 i-PMMA 的分离。此外，发现使用非立体络合溶剂（如氯仿）可以分离 s-PMMA 和 i-PMMA 的混合物。最后，确定 AF4 通道温度对 PMMA 样品的保留行为有影响。对于 THF 作为载体液，发现 s-PMMA 和 i-PMMA 之间的最大保留差异可以在通道温度为 35°C 时达到。对于 ACN 作为载体液，观察到 i-PMMA 的保留行为受温度变化的影响明显大于 s-PMMA 和 a-PMMA。
