Department of Chemistry, Umeå University, Umeå, Sweden.
J Sep Sci. 2010 Feb;33(2):191-9. doi: 10.1002/jssc.200900668.
Nitroxide-mediated polymerization was used as a model system for preparing styrenic monolithic materials with significant mesopore contents in different mold formats, with the aim of assessing the validity of pore characterization of capillary monoliths by analysis of parallel bulk polymerized precursor solution. Capillary monoliths were prepared in 250 microm id fused silica tubes (quadruplicate samples, in total 17 m), and the batch polymerizations were carried out in parallel in 100 microL microvials and regular 2 mL glass vials, both in quintuplicate. The monoliths recovered from the molds were characterized for their meso- and macroporous properties by nitrogen sorptiometry (three repeated runs on each sample), followed by a single analysis by mercury intrusion porosimetry. A total of 14 monolith samples were thus analyzed. A Grubbs' test identified one regular vial sample as an outlier in the sorptiometric surface area measurements, and data from this sample were consequently excluded from the pore size calculations, which are based on the same nitrogen sorption data, and also from the mercury intrusion data set. The remaining data were subjected to single factor analyses of variance analyses to test if the porous properties of the capillary monoliths were different from those of the bulk monoliths prepared in parallel. Significant differences were found between all three formats both in their meso- and macroporous properties. When the dimension was shrunk from conventional vial to capillary size, the specific surface area decreased from 52.2+/-4.7 to 34.6+/-1.7 m(2)/g. This decrease in specific surface area was accompanied by a significant shift in median diameter of the through-pores, from 310+/-3.9 to 544+/-13 nm. None of these differences were obvious from the scanning electron micrographs that were acquired for each sample type. The common practice of determining the mesopore characteristics from analysis of samples prepared by parallel bulk polymerization and looking for changes in the macropore structure by visual assessment of SEMs are therefore both rather questionable, at least for monoliths of the kind used in this study.
氮氧自由基引发聚合被用作模型体系，用于在不同的模具形式下制备具有显著中孔含量的苯乙烯型整体材料，目的是通过分析平行的本体聚合前体溶液来评估毛细整体的孔结构表征的有效性。在 250μm id 的熔融石英管中制备毛细整体（4 个重复样品，总计 17m），并在 100μL 微管和常规 2mL 玻璃管中平行进行批聚合（每个重复 5 次）。从模具中回收的整体通过氮气吸附法（对每个样品进行 3 次重复运行）对其中孔和大孔性质进行表征，然后通过单点汞侵入法进行分析。总共分析了 14 个整体样品。Grubbs 检验确定了一个常规管样品在比表面积测量中的一个异常值，因此该样品的数据从孔径计算中排除，该计算基于相同的氮气吸附数据，并且也从汞侵入数据集排除。其余数据进行单因素方差分析，以检验毛细整体的多孔性质是否与平行制备的本体整体不同。在所有三种形式中都发现了中孔和大孔性质的显著差异。当尺寸从常规管缩小到毛细尺寸时，比表面积从 52.2+/-4.7 降至 34.6+/-1.7m(2)/g。这种比表面积的减小伴随着通过孔的中值直径的显著变化，从 310+/-3.9 降至 544+/-13nm。这些差异在对每种样品类型都进行了扫描电子显微镜（SEM）拍摄的图像中并不明显。因此，从平行本体聚合制备的样品分析中确定中孔特征并通过 SEM 进行宏观结构变化的目视评估的常见做法至少对于本研究中使用的整体是值得怀疑的。
