Chang Boyce S, Ma Le, He Mengdi, Xu Ting
Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California 94720, United States.
Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
ACS Macro Lett. 2020 Jul 21;9(7):1060-1066. doi: 10.1021/acsmacrolett.0c00434. Epub 2020 Jul 7.
Hierarchical assemblies from block copolymer (BCP)-based supramolecules have shown immense potential as programmable materials owing to their versatility for incorporating functional molecules and provide access to arrays of hierarchical structures. However, there remains a knowledge gap on the formation of the supramolecule in solution. Here, we applied NMR techniques to investigate the solution-phase behavior of the most studied supramolecular systems, polystyrene--poly(4-vinylpyridine)(3-pentadecylphenol) (PS--P4VP(PDP)). The results show that the supramolecule likely adopts a coil-comb conformation, despite the small molecule's (PDP) rapid exchange between the bonded and free states. The exchange rate (>10 s) exceeds the NMR time scale at the frequency of interest. The supramolecules form under dilute conditions (∼2 vol %) and are attributed to the enthalpic gain of the hydrogen bonding between the PDP and 4VP. As the solute concentration increases (>10 vol %), the supramolecule forms micelle-like aggregates with PDP accumulated within the comb-block's pervaded volume based on analysis of the apparent molecular weight, viscosity, and chain dynamics. This work sheds light on the long-standing question regarding the evolution of the constituents in the BCP-based supramolecule in solution and provides valuable guidance toward their solution-based processing and morphological control.
基于嵌段共聚物（BCP）的超分子的分级组装体，由于其在结合功能分子方面的多功能性以及能够形成分级结构阵列，已显示出作为可编程材料的巨大潜力。然而，关于溶液中超分子的形成仍存在知识空白。在此，我们应用核磁共振（NMR）技术来研究研究最多的超分子体系——聚苯乙烯-聚（4-乙烯基吡啶）（3-十五烷基苯酚）（PS-P4VP（PDP））的溶液相行为。结果表明，尽管小分子（PDP）在键合态和游离态之间快速交换，但超分子可能采取线圈-梳状构象。在感兴趣的频率下，交换速率（>10 s）超过了NMR时间尺度。超分子在稀溶液条件下（约2体积%）形成，这归因于PDP与4VP之间氢键的焓增。随着溶质浓度增加（>10体积%），基于表观分子量、粘度和链动力学分析，超分子形成类似胶束的聚集体，PDP聚集在梳状嵌段的渗透体积内。这项工作揭示了关于基于BCP的超分子在溶液中组分演化的长期问题，并为其基于溶液的加工和形态控制提供了有价值的指导。
