Crystallinity and perfection in ethylene vitrimers probed by combined calorimetry, scattering, and time-domain NMR
Crystallinity and perfection in ethylene vitrimers probed by combined calorimetry, scattering, and time-domain NMR
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DOI：
10.3389/frsfm.2023.1208777
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发表时间：
2023-06
期刊：
影响因子：
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通讯作者：
K. Saalwächter;Bhaskar Soman;C. M. Evans
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文献类型：
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作者：
K. Saalwächter;Bhaskar Soman;C. M. Evans
本文用时域核磁共振研究了乙撑三聚体的结晶动力学和晶-晶转变动力学。这些玻璃体先前表现出多晶型转变的晶体结构，这是在这里示出可区分的NMR通过其偶极线宽度的基础上不同的质子密度和快速的内部运动。通过时间分辨的NMR实验确定了形成和相互转化的多晶型物的条件，重点是在完全和部分熔融后的重结晶。DSC实验被用来澄清一个意想不到的过热效应，这对实际熔点的测定提出了挑战。我们进一步确定了一个强大的记忆效应在等温（再）结晶。的动态性质的vitromers结晶动力学的影响进行了讨论。我们发现，内部完善的晶体，使由vitrimeric交换过程中，可以有一个很大的影响DSC检测的熔化焓，而不改变整体结晶度。
The kinetics of crystallization and crystal-crystal transformations in ethylene vitrimers are studied by time-domain NMR. These vitrimers previously exhibited polymorphic transition of crystal structures, which are shown here to be distinguishable by NMR via their dipolar line widths based upon different proton densities and fast internal motions. The conditions under which the polymorphs are formed and interconvert are identified via time-resolved NMR experiments, with a focus on recrystallization after full and partial melting. DSC experiments are used to clarify an unexpected superheating effect, which challenges the determination of actual melting points. We further identify a strong memory effect in isothermal (re)crystallization. Implications of the dynamic nature of the vitrimers in relation to the kinetics of crystallization are discussed. We find that internal perfecting of crystals, enabled by the vitrimeric exchange process, can have a large effect on the DSC-detected melting enthalpy without change in overall crystallinity.