Effect of Polymer Melt Memory as Studied by Nuclear Magnetic Resonance

今年修复了一个高温核磁共振探头，并在加热和冷却过程中对聚环氧乙烷(PEO)和石蜡进行了原位核磁共振测量。Mn=4,600的PEO样品的起始粉末图谱与加热后冷却后的光谱没有任何差异，表明没有取向。石蜡的光谱开始于典型的σ_lt；11&gt；，σ_&lt；22&gt；，σ_&lt；33&gt；系统的粉末状花样，然后加热时转变为σ_&lt；11&gt；=σ_&lt；22&gt；型花样。这是由于六方相的相变所致。融化后，宽峰变成了窄峰。在冷却过程中，熔体通过六方相，在该相上，高场σ_lt；33&gt；成分的减少表明了磁取向。这意味着链(33方向)垂直于磁场对齐。这与之前的X射线分析结果一致。

A high-temperature NMR probe became repaired this year and the in-situ NMR measurements for poly(ethylene oxide) (PEO) and paraffin were carried out during the heating and cooling processes. The PEO sample of Mn=4,600 did not show any difference between the starting powder pattern and the spectrum obtained after heating followed by cooling, indicating no alignment. But the sample of Mn=2,000 exhibited the difference, indicating magnetic alignment.The spectrum of paraffin starts with a powder pattern typical of a σ_<11>, σ_<22>, σ_<33> system, then changed to σ_<11> = σ_<22> type pattern upon heating. This is due to the phase change to the hexagonal phase. Upon melting, the broad peak changed to a narrow one. During the cooling process, the melt passes through a hexagonal phase at which the magnetic alignment was indicated by the reduction of the high-field σ_<33> component. This means that the chain (33 direction) aligned perpendicular to the magnetic field. This is consistent with the previous results by X-ray.