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针，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= 4600的PEO样品的起始粉末图案与加热后冷却后得到的光谱没有任何差异，说明没有对齐。但Mn= 2000的样品表现出这种差异，表明磁性排列。石蜡的光谱开始表现为σ_<11>、σ_<22>、σ_<33>型，加热后转变为σ_<11> = σ_<22>型。这是由于相变到六边形相。融化后，宽峰变成窄峰。在冷却过程中，熔体经过一个六角形相，高场σ_<33>分量的减小表明熔体的磁向。这意味着链（33方向）垂直于磁场排列。这与先前的x射线结果一致。

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.