Polymer Dynamics in Nanostructured Environments: Structure-Property Relations Unraveled by Dielectric Spectroscopy
Polymer Dynamics in Nanostructured Environments: Structure-Property Relations Unraveled by Dielectric Spectroscopy
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DOI：
10.1021/bk-2021-1375.ch010
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发表时间：
2021
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影响因子：
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通讯作者：
M. Tress;M. Vielhauer;P. Lutz;R. Mülhaupt;F. Kremer;Kunyue Xing;Sirui Ge;P. Cao;Tomonori Saito;A. Sokolov
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文献类型：
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作者：
M. Tress;M. Vielhauer;P. Lutz;R. Mülhaupt;F. Kremer;Kunyue Xing;Sirui Ge;P. Cao;Tomonori Saito;A. Sokolov
许多聚合物表现出复杂的分子和超分子组织水平，特别是当它们的化学结构本身表现出更高的复杂性时。这种内部的纳米结构通常伴随着改变的动力学，这反过来又影响宏观性能。利用这一点来设计非常理想的性能，例如，机械稳定性、运输功能或自我修复，需要详细了解化学结构和相应的动力学变化之间的相互关系。探索聚合物动力学的一个通用工具是介电光谱学，如两个例子所示。第一种情况是具有多面体低聚硅氧烷核的半结晶星形聚合物；由于这种分子的不寻常结构，部分结晶限制了无定形区域的链构象并导致加速的链段松弛-与通常观察到的半结晶聚合物中较慢的动力学形成鲜明对比。对提取的驰豫时间分布(RTD)的详细分析表明，有三个独立的非晶区，它们具有不同的动力学特性。在第二个例子中，研究了介相分离对缔合遥控聚合物的影响。在这些基于聚二甲基硅氧烷的材料中，氢键末端基团相分离，伴随着RTD的极大加宽，这表明对链段动力学的严格限制。再次，提出了改变的链构象，这为在互补剪切模数测量中发现的极大增强的橡胶平台提供了定性的解释。在这两个例子中，除了纳米结构环境对动力学的严重影响外，介电光谱还揭示了导致宏观机械性能改善的微妙结构细节。
Many polymers exhibit complex levels of molecular and supramolecular organization, particularly if their chemical structure shows an increased complexity itself. This internal nanoscale-structuring is often accompanied by altered dynamics which in turn affects the macroscopic performance. Using this to design highly desired properties, e.g., mechanical stability, transport functions or self-healing, requires a detailed understanding of the interrelation between chemical structure and the corresponding change in dynamics. A versatile tool to explore polymer dynamics is dielectric spectroscopy, as demonstrated in two examples. The first case is a semi-crystalline star-polymer with a polyhedral oligomeric silesquioxane core; due to the unusual architecture of this molecule, the partial crystallization constrains the chain conformations in the amorphous regions and results in an accelerated segmental relaxation–in stark contrast to the commonly observed slower dynamics in semi-crystalline polymers. A detailed analysis of the extracted relaxation time distribution (RTD) reveals three separate amorphous regions with different dynamics. In a second example, the impact of meso-phase separation in associating telechelic polymers is studied. The hydrogen-bonding end groups in these polydimethylsiloxane-based materials phase separate, which is accompanied by a tremendously broadened RTD indicating severe constraints on the segmental dynamics. Again, altered chain conformations are proposed which offer a qualitative explanation for the tremendously enhanced rubbery plateau found in complimentary shear modulus measurements. In both examples, beyond the severe impact of nanostructured environments on the dynamics, dielectric spectroscopy also reveals subtle structural details leading to an improved macroscopic mechanical performance.