Department of Chemistry & Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA.
Anal Bioanal Chem. 2010 Feb;396(4):1589-98. doi: 10.1007/s00216-009-3320-9. Epub 2009 Dec 13.
We present a method by which to obtain the absolute, chemical-heterogeneity-corrected molar mass (M) averages and distributions of copolymers and apply the method to a gradient random copolymer of styrene and methyl methacrylate in which the styrene percentage decreases from approximately 30% to 19% as a function of increasing molar mass. The method consists of separation by size-exclusion chromatography (SEC) with detection using multi-angle static light scattering (MALS), differential viscometry (VISC), differential refractometry (DRI), and ultraviolet absorption spectroscopy (UV) and relies on the preferential absorption of styrene over methyl methacrylate at 260 nm. Using this quadruple-detector SEC/MALS/UV/VISC/DRI approach, the percentage of styrene (%St) in each elution slice is determined. This %St is then used to determine the specific refractive index increment, corrected for chemical composition, at each elution slice, which is then used to obtain the molar mass at each slice, corrected for chemical composition. From this corrected molar mass and from the chemical-composition-corrected refractometer response, the absolute, chemical-heterogeneity-corrected molar mass averages and distribution of the copolymer are calculated. The corrected molar mass and intrinsic viscosity at each SEC elution slice are used to construct a chemical-heterogeneity-corrected Mark-Houwink plot. The slice-wise-corrected M data are used, in conjunction with the MALS-determined R(G,z ) of each slice, to construct a conformation plot corrected for chemical heterogeneity. The corrected molar mass distribution (MMD) of the gradient copolymer extends over an approximately 30,000 g/mol wider range than the uncorrected MMD. Additionally, correction of the Mark-Houwink and conformation plots for the effects of chemical heterogeneity shows that the copolymer adopts a more compact conformation in solution than originally concluded.
我们提出了一种方法，可以获得共聚物的绝对、化学不均一性校正的重均分子量（M）平均值和分布，并将该方法应用于苯乙烯和甲基丙烯酸甲酯的梯度无规共聚物中，其中苯乙烯的百分比从大约 30%到 19%随摩尔质量的增加而降低。该方法包括使用多角静态光散射（MALS）、差示黏度计（VISC）、差示折射计（DRI）和紫外吸收光谱（UV）进行尺寸排阻色谱（SEC）分离，并依赖于苯乙烯在 260nm 处对甲基丙烯酸甲酯的优先吸收。使用这种四重检测器 SEC/MALS/UV/VISC/DRI 方法，确定每个洗脱切片中的苯乙烯百分比（%St）。然后，将该%St用于确定每个洗脱切片的化学组成校正后的特定折射率增量，然后用于获得每个切片的化学组成校正后的摩尔质量。从该校正后的摩尔质量和化学组成校正后的折射仪响应，计算出共聚物的绝对、化学不均一性校正的重均分子量平均值和分布。在每个 SEC 洗脱切片上的校正摩尔质量和特性黏度用于构建化学不均一性校正的 Mark-Houwink 图。使用 SEC 每个洗脱切片的切片校正摩尔质量和特性黏度来构建校正化学不均一性的构象图。梯度共聚物的切片校正 M 数据与每个切片的 MALS 确定的 R(G,z )一起用于构建校正化学不均一性的构象图。经化学不均一性校正的摩尔质量分布（MMD）比未经校正的 MMD 宽约 30000g/mol。此外，对 Mark-Houwink 和构象图进行化学不均一性校正表明，共聚物在溶液中比最初得出的结论具有更紧凑的构象。
