Impact of Backbone Rigidity on the Thermomechanical Properties of Semiconducting Polymers with Conjugation Break Spacers
Impact of Backbone Rigidity on the Thermomechanical Properties of Semiconducting Polymers with Conjugation Break Spacers
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DOI：
10.1021/acs.macromol.0c00889
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发表时间：
2020-07-28
期刊：
影响因子：
5.5
通讯作者：
Gu, Xiaodan
中科院分区：
文献类型：
--
作者：
Galuska, Luke A.;McNutt, William W.;Gu, Xiaodan
对于主链刚性对共轭聚合物热机械性能的作用仍然缺乏基本的了解。在这里，我们提供了第一个整体方法，通过插入柔性共轭断裂间隔基（CBS）来了解主链刚性对 n 型萘二酰亚胺基共轭聚合物（用 PNDI-Cx 表示）的基本影响。 CBS 长度各不相同，从完全缀合的零烷基间隔基 (PNDI-C0) 到七碳烷基间隔基 (PNDI-C7)，CBS 被设计到每个重复单元中以进行系统评估。采用溶液小角中子散射和振荡剪切流变测定法提供了 CBS 对共轭聚合物链刚性和缠结分子量 (M-e) 影响的第一个定量证据，证明完全共轭的 PNDI-C0 和 PNDI-C6 的库恩长度分别从 521 埃减少到 36 埃，并且 M-e 几乎一致，约为 15 添加 CBS 后的 kDa。弹性模量和玻璃化转变温度等热机械性能随着 CBS 长度的增加而降低。高分子量 PNDI-C4 具有非凡的延展性，断裂前拉伸应变高达 400% 以上，我们将其归因于大量的缠结和结晶破坏。此外，通过 X 射线衍射、偏振紫外可见光谱和原子力显微镜研究了 PNDI-Cx 在应变下的变形机制。总的来说，这项工作揭示了主链刚性在设计柔性和可拉伸共轭聚合物中的重要作用。
There remains a lack of fundamental understanding in the role of backbone rigidity on the thermomechanical properties of conjugated polymers. Here, we provide the first holistic approach to understand the fundamental influence of backbone rigidity on an n-type naphthalene diimide-based conjugated polymer, denoted by PNDI-Cx, through insertion of a flexible conjugation break spacer (CBS). CBS lengths are varied from fully conjugated with zero alkyl spacer (PNDI-C0) to a sevencarbon alkyl spacer (PNDI-C7), with the CBS engineered into each repeat unit for systematic evaluation. Solution small-angle neutron scattering and oscillatory shear rheometry were employed to provide the first quantitative evidence of CBS influence over conjugated polymer chain rigidity and entanglement molecular weight (M-e), demonstrating a reduction in the Kuhn length from 521 to 36 angstrom for fully conjugated PNDI-C0 and PNDI-C6, respectively, as well as a nearly consistent M-e of similar to 15 kDa upon the addition of CBS. Thermomechanical properties, such as elastic modulus and glass-transition temperature, were shown to decrease with an increasing length of CBS. An extraordinary ductility, upwards of 400% tensile strain before fracture, was observed for high-molecular-weight PNDI-C4, which we attribute to a high number of entanglements and disruption of crystallization. Furthermore, the deformation mechanism for PNDI-Cx was studied under strain through X-ray diffraction, polarized UV-vis spectroscopy, and atomic force microscopy. Overall, this work sheds light on the important role of backbone rigidity in designing flexible and stretchable conjugated polymers.