Materials Chemistry Division, Chemistry Department , University of Helsinki , AI Virtasen Aukio 1 , Helsinki , Finland.
Department of Chemical Engineering , McMaster University , Hamilton , Ontario , Canada.
Biomacromolecules. 2018 Jul 9;19(7):2708-2720. doi: 10.1021/acs.biomac.8b00295. Epub 2018 Apr 11.
Recent developments in ionic liquid electrolytes for cellulose or biomass dissolution has also allowed for high-resolution H and C NMR on very high molecular weight cellulose. This permits the development of advanced liquid-state quantitative NMR methods for characterization of unsubstituted and low degree of substitution celluloses, for example, surface-modified nanocelluloses, which are insoluble in all molecular solvents. As such, we present the use of the tetrabutylphosphonium acetate ([P][OAc]):DMSO- d electrolyte in the 1D and 2D NMR characterization of poly(methyl methacrylate) (PMMA)-grafted cellulose nanocrystals (CNCs). PMMA- g-CNCs was chosen as a difficult model to study, to illustrate the potential of the technique. The chemical shift range of [P][OAc] is completely upfield of the cellulose backbone signals, avoiding signal overlap. In addition, application of diffusion-editing for H and HSQC was shown to be effective in the discrimination between PMMA polymer graft resonances and those from low molecular weight components arising from the solvent system. The bulk ratio of methyl methacrylate monomer to anhydroglucose unit was determined using a combination of HSQC and quantitative C NMR. After detachment and recovery of the PMMA grafts, through methanolysis, DOSY NMR was used to determine the average self-diffusion coefficient and, hence, molecular weight of the grafts compared to self-diffusion coefficients for PMMA GPC standards. This finally led to a calculation of both graft length and graft density using liquid-state NMR techniques. In addition, it was possible to discriminate between triads and tetrads, associated with PMMA tacticity, of the PMMA still attached to the CNCs (before methanolysis). CNC reducing end and sulfate half ester resonances, from sulfuric acid hydrolysis, were also assignable. Furthermore, other biopolymers, such as hemicelluloses and proteins (silk and wool), were found to be soluble in the electrolyte media, allowing for wider application of this method beyond just cellulose analytics.
最近，离子液体电解质在纤维素或生物质溶解方面的发展也允许对非常高分子量的纤维素进行高分辨率的 H 和 C NMR 分析。这使得可以开发先进的液态定量 NMR 方法，用于表征未取代和低取代度的纤维素，例如，表面改性的纳米纤维素，它们在所有分子溶剂中都不溶。因此，我们提出了在 1D 和 2D NMR 表征聚（甲基丙烯酸甲酯）（PMMA）接枝纤维素纳米晶体（CNC）时使用四丁基磷酸乙酸酯（[P][OAc]）：DMSO- d 电解质。选择 PMMA-g-CNC 作为一个困难的模型来研究，以说明该技术的潜力。[P][OAc] 的化学位移范围完全在纤维素主链信号的场强范围内，避免了信号重叠。此外，还展示了对 H 和 HSQC 进行扩散编辑在区分 PMMA 聚合物接枝共振与溶剂体系中低分子量成分的共振方面是有效的。通过 HSQC 和定量 C NMR 的组合，确定了甲基丙烯酸甲酯单体与脱水葡萄糖单元的体比。通过甲醇解分离和回收 PMMA 接枝后，使用 DOSY NMR 确定了与 PMMA GPC 标准的自扩散系数相比，接枝的平均自扩散系数和分子量。这最终导致使用液态 NMR 技术计算接枝长度和接枝密度。此外，还可以区分与 PMMA 立构规整性相关的仍连接到 CNC 的 PMMA 的三聚体和四联体（在甲醇解之前）。通过硫酸水解，还可以分配 CNC 还原端和半酯硫酸盐的共振。此外，还发现其他生物聚合物，如半纤维素和蛋白质（丝和羊毛），可溶于电解质介质中，使得该方法的应用范围不仅限于纤维素分析。
