The State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University , Chengdu 610065, China.
Biomacromolecules. 2017 Apr 10;18(4):1440-1448. doi: 10.1021/acs.biomac.7b00367. Epub 2017 Mar 24.
Self-assembly nucleators have been increasingly used to manipulate the crystallization of PLLA due to their strong intermolecular interaction with PLLA, while the molecular mechanism of such interaction is still unrevealed. In present work, one special self-assembly nucleator (TMC-300) with relatively high solubility in PLLA matrix, is chosen to investigate how the interaction works at molecular level to promote the crystallization of PLLA mainly through time-resolved spectroscopy. The results indicate that due to the dipole-dipole NH···O═C interaction between dissolved TMC-300 and PLLA, PLLA chains are transformed into gt conformer before TMC-300 phase-separating from PLLA melt, resulting in low energy barrier to pass for the following formation of PLLA α-crystal (α-crystal is consisted of gt conformer). Once the dissolved TMC-300 starts to self-assemble into frameworks upon cooling, the transformed PLLA chains with high population of gt conformer form the primary nuclei on the surface of such self-assembling TMC-300 frameworks. For the first time, not only the heterogeneous nucleation but also the conformational regulation of PLLA chains are proved to be responsible for the high efficiency of the self-assembly nucleators (TMC-300) in promoting the crystallization of PLLA. Therefore, conformational regulation is proposed for crystalline manipulation of PLLA, and this work brings new insight on promoting the crystallization of PLLA even other polymers by regulating their molecular conformation.
自组装成核剂由于与 PLLA 之间的强分子间相互作用，已越来越多地被用于操纵 PLLA 的结晶，而这种相互作用的分子机制仍未被揭示。在本工作中，选择了一种具有相对较高 PLLA 基体溶解度的特殊自组装成核剂（TMC-300），主要通过时间分辨光谱研究这种相互作用如何在分子水平上促进 PLLA 的结晶。结果表明，由于溶解的 TMC-300 与 PLLA 之间的 NH···O═C 偶极-偶极相互作用，TMC-300 从 PLLA 熔体中相分离之前，PLLA 链转变成 gt 构象，导致随后形成 PLLA α-晶体（α-晶体由 gt 构象组成）的能量势垒较低。一旦溶解的 TMC-300 在冷却时开始自组装成框架，具有高比例 gt 构象的转变 PLLA 链就在这种自组装 TMC-300 框架表面形成初级核。首次证明，自组装成核剂（TMC-300）不仅具有异相成核作用，而且对 PLLA 链的构象调节都有助于其促进 PLLA 结晶的高效性。因此，提出了构象调节用于 PLLA 的结晶操纵，这项工作为通过调节其分子构象来促进 PLLA 甚至其他聚合物的结晶提供了新的见解。
