School of Polymer Science and Polymer Engineering, The University of Akron, Akron, Ohio 44325-3909, United States.
State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China.
ACS Macro Lett. 2022 Mar 15;11(3):284-288. doi: 10.1021/acsmacrolett.1c00789. Epub 2022 Feb 8.
There are long-standing debates in crystallization mechanism of polymer chains at the molecular levels: Which comes first, chain folding or lamellae formation during crystallization? In this study, we report the local chain trajectory of C-labeled semicrystalline polymer in an extreme case of rapidly quenched glassy state as well as thermodynamically stable crystals formed via different pathways from glass and melt. Magnetically dipole interactions do not require a long-range order of molecular objects and thus enable us to trace the local chain trajectory of polymer chains even in a glassy state. To accurately characterize the local chain trajectory of polymer glass, the natural abundance effect on C-C double-quantum (DQ) nuclear magnetic resonance (NMR) signal is re-examined using extended chain conformation. As results, it is found that glassy chains adopt the same adjacent re-entry structure (adjacent re-entry number, = 1) with the melt- and cold-grown crystals. From these results, it is concluded that (i) folding occurs prior to crystallization and (ii) melt and cold crystallization do not induce additional folding but proceed with rearrangements of polymer chains in the existing templates.
在结晶过程中，是链折叠还是片晶形成先发生？在这项研究中，我们报告了 C 标记的半晶聚合物在快速淬火玻璃态以及通过玻璃态和熔体形成的不同途径形成的热力学稳定晶体中的局部链轨迹。磁偶极相互作用不需要分子物体的长程有序，因此即使在玻璃态下，我们也能够追踪聚合物链的局部链轨迹。为了准确描述聚合物玻璃的局部链轨迹，使用扩展链构象重新检查了 C-C 双量子（DQ）核磁共振（NMR）信号的天然丰度效应。结果发现，玻璃态链采用与熔体和低温生长晶体相同的相邻重入结构（相邻重入数， = 1）。根据这些结果，可以得出结论：（i）折叠先于结晶发生；（ii）熔体和低温结晶不会诱导额外的折叠，而是通过现有模板中聚合物链的重排进行。
