Immobilized 13 C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR
Immobilized 13 C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR
复制标题
通过高级 NMR 检测到固定化 13 C 标记的聚醚链末端局限于微晶表面
DOI：
10.1126/sciadv.abc0059
复制
发表时间：
2020
期刊：
影响因子：
13.6
通讯作者：
Schmidt-Rohr, Klaus
中科院分区：
文献类型：
--
作者：
Yuan, Shichen;Schmidt-Rohr, Klaus
一个综合的13 C核磁共振（NMR）的方法来表征聚醚和聚酯的链端的位置，在微晶表面或在无定形层，提出。用13 COO-乙酰基标记聚甲醛的OH链端，并用13 C NMR结合化学位移各向异性（CSA）再耦合研究其动力学。至少四分之三的链端不是移动的悬垂纤毛，而是固定的，表现出结晶环境和快速CSA失相的粉末图案特征。通过自旋扩散分析了固定化链端的位置和聚集。从非晶区的快速1H自旋扩散显示限制链端的微晶表面，证实了链端之间的快速13 C自旋交换。这些观察结果证实了避免密度异常的原理，这需要链终止于微晶表面以远离拥挤的界面层。
A comprehensive13C nuclear magnetic resonance (NMR) approach for characterizing the location of chain ends of polyethers and polyesters, at the crystallite surface or in the amorphous layers, is presented. The OH chain ends of polyoxymethylene are labeled with13COO-acetyl groups and their dynamics probed by13C NMR with chemical shift anisotropy (CSA) recoupling. At least three-quarters of the chain ends are not mobile dangling cilia but are immobilized, exhibiting a powder pattern characteristic of the crystalline environment and fast CSA dephasing. The location and clustering of the immobilized chain ends are analyzed by spin diffusion. Fast1H spin diffusion from the amorphous regions shows confinement of chain ends to the crystallite surface, corroborated by fast13C spin exchange between chain ends. These observations confirm the principle of avoidance of density anomalies, which requires that chains terminate at the crystallite surface to stay out of the crowded interfacial layer.