克服"扩散极限" - - 通过扩散有序NMR测量高摩尔质聚合物所需的原理
Thomas Swift1, Edward Dyson1, Natalia Koniuch1
1Polymer and Biomaterials Chemistry Laboratory, Department of Chemistry and Biosciences, University of Bradford, Bradford, BD7 1DP, United Kingdom.
使用扩散NMR精确测量聚合物大小,需要考虑溶液中的粘度. 这项研究展示了如何纠正粘度效应,从而能够精确确定大型宏分子的水力动力半径.
科学领域:
- 聚合物化学 聚合物化学
- 分析化学 分析化学
- 核磁共振 (NMR) 光谱学 核磁共振 (NMR) 光谱学
背景情况:
- 扩散NMR越来越多地用于聚合物大小分析.
- 溶液中的粘度使NMR输出复杂化,需要专门的方法.
- 精确的水力动力半径测定对于高摩尔质量或分散性聚合物至关重要.
研究的目的:
- 为了研究溶液内粘度对使用DOSY NMR的聚合物尺寸测定的影响.
- 开发和验证用于精确的水力动力半径测量宏分子的方法.
- 扩大扩散NMR的适用性到高摩尔质量和高粘度系统.
主要方法:
- 在多种聚合物类型和溶剂中通过DOSY NMR利用扩散测量.
- 采用适用于纯溶剂粘度的粘度校正因子来确定溶液内粘度.
- 研究了一个扩散优化的NMR探针 (Bruker DiffBB) 的性能.
主要成果:
- 对于各种聚合物 (PEG,PEO,PS,PMMA,PNIPAM) 确定的水力动力半径与文献值相比显示出高准确度.
- 在溶液中的粘度显著影响扩散NMR输出,在低粘度溶剂中变异性更高.
- 实验范围扩展到分子质量超过100万g/mol的聚合物和高粘度溶液.
- 一个扩散优化的NMR探针有效地准缓慢扩散的化学物种.
结论:
- 溶液中的粘度受到高摩尔质量聚合物的微量影响,导致扩散NMR数据中的系统偏移.
- DOSY NMR测量,包括溶剂扩散,可以自行纠正这些粘度效应.
- 这种方法可以在没有外部标准的情况下准确预测大型,缓慢扩散的材料的水力动力半径和摩尔质量.
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