Extensive efforts have been made to develop flexible electronics with conjugated polymers that are intrinsically stretchable and soft. We recently systematically investigated the influence of conjugation break spacers (CBS) on the thermomechanical properties of a series n-type naphthalene diimide-based conjugated polymer and found that CBS can significantly reduce chain rigidity, melting point, as well as glass transition temperature. In the current work, we further examined the influence of CBS on the crystallization behaviors of PNDI-C3 to C6, including isothermal crystallization kinetics, crystal polymorphism and subsequently time-dependent modulus, in a holistic approach using differential scanning calorimetry, X-ray scattering, polarized optical microscopy, atomic force microscopy, and pseudo-free-standing tensile test. Results demonstrate that increasing the length of CBS increases the crystallization half-time by 1 order of magnitude from PNDI-C3 to PNDI-C6 from approximately 10³ to 10⁴ s. The crystallization rate shows a bimodal dependence on the temperature due to the presence of different polymorphs. In addition, crystallization significantly affects the mechanical response, a stiffening in the modulus of nearly three times is observed for PNDI-C5 when annealed at room temperature for 12 h. Crystallization kinetic is also influenced by molecular weight (MW). Higher MW PNDI-C3 crystallizes slower. In addition, an odd–even effect was observed below 50°C, odd-number PNDI-Cxs (C3 and C5) crystallize slower than the adjacent even-numbered PNDI-Cxs (C4 and C6). Our work provides an insight to design flexible electronics by systematically tuning the mechanical properties through control of polymer crystallization by tuning backbone rigidity.

中文翻译：

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共轭聚合物结晶行为和薄膜机械稳定性的主链柔性

已经做出了广泛的努力来开发具有本质上可拉伸和柔软的共轭聚合物的柔性电子产品。我们最近系统地研究了共轭断裂间隔物 (CBS) 对一系列 n 型萘二亚胺基共轭聚合物热机械性能的影响，发现 CBS 可以显着降低链刚度、熔点以及玻璃化转变温度。在目前的工作中，我们进一步研究了 CBS 对 PNDI-C3 至 C6 结晶行为的影响，包括等温结晶动力学、晶体多晶型和随后的时间依赖性模量，采用差示扫描量热法、X 射线散射的整体方法、偏光显微镜、原子力显微镜和伪独立拉伸试验。³到 10 ⁴ 秒。由于存在不同的多晶型物，结晶速率显示出对温度的双峰依赖性。此外，结晶显着影响机械响应，当在室温下退火 12 小时时，PNDI-C5 的模量变硬了近三倍。结晶动力学也受分子量 (MW) 的影响。较高的 MW PNDI-C3 结晶较慢。此外，在 50°C 以下观察到奇偶效应，奇数 PNDI-Cxs（C3 和 C5）的结晶速度比相邻的偶数 PNDI-Cxs（C4 和 C6）慢。我们的工作通过调节骨架刚度来控制聚合物结晶来系统地调节机械性能，从而为设计柔性电子产品提供了一种见解。