Bichler Karin J, Jakobi Bruno, Schneider Gerald J
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
Macromolecules. 2021 Feb 23;54(4):1829-1837. doi: 10.1021/acs.macromol.0c02104. Epub 2021 Feb 3.
Different polymer architectures behave differently regarding their dynamics. We have used a combination of dielectric spectroscopy, and fast field cycling nuclear magnetic resonance (NMR) to compare the dynamical behavior of two different polymer architectures, with similar overall molecular weight. The systems of interest are a bottlebrush polymer and a linear one, both based on poly(dimethylsiloxane) (PDMS). To verify the structure of the PDMS-g-PDMS bottlebrush in the melt, small-angle neutron scattering was used, yielding a spherical shape. Information about the segmental dynamics was revealed by dielectric spectroscopy and extended to higher temperatures by fast field cycling NMR. One advantage of fast field cycling NMR is the detection of large-scale chain dynamics, which dielectric spectroscopy cannot probe for PDMS. While segmental relaxation seems to be independent of the architecture, the large-scale chain dynamics show substantial differences, as represented by the mean square displacement. Here, two regions are detected for each polymer. The linear polymer shows the Rouse regime, followed by reptation. In contrast, the bottlebrush polymer performs Rouse dynamics and diffusion in the available time window, and entanglement effects are completely missing.
不同的聚合物结构在动力学方面表现各异。我们结合了介电谱和快速场循环核磁共振（NMR）来比较两种具有相似总分子量的不同聚合物结构的动力学行为。所关注的体系是一种基于聚二甲基硅氧烷（PDMS）的刷状聚合物和一种线性聚合物。为了验证熔体中PDMS-g-PDMS刷状聚合物的结构，使用了小角中子散射，结果显示其为球形。通过介电谱揭示了有关链段动力学的信息，并通过快速场循环NMR将其扩展到更高温度。快速场循环NMR的一个优点是能够检测大规模链动力学，而介电谱无法探测PDMS的这一特性。虽然链段弛豫似乎与聚合物结构无关，但大规模链动力学表现出显著差异，以均方位移表示。在此，每种聚合物都检测到两个区域。线性聚合物表现出Rouse区域，随后是蠕动。相比之下，刷状聚合物在可用的时间窗口内进行Rouse动力学和扩散，并且完全没有缠结效应。
