Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
J Am Chem Soc. 2010 Oct 13;132(40):14251-60. doi: 10.1021/ja106362w.
The ability to finely tune the solution viscosity of an aqueous system is critical in many applications ranging from large-scale fluid-based industrial processes to free-standing hydrogels important in regenerative medicine, controlled drug delivery, and 'green' self-healing materials. Herein we demonstrate the use of the macrocyclic host molecule cucurbit[8]uril (CB[8]) to facilitate reversible cross-linking of multivalent copolymers with high binding constants (K(a) > 10(11)-10(12) M(-2)) leading to a supramolecular hydrogel. Multivalent copolymers were prepared by free radical polymerization techniques and contained either pendant methyl viologen (a good first guest for CB[8]) or naphthoxy derivatives (good second guests for CB[8]). A colorless solution of the two multivalent copolymers bearing first and second guests, respectively, can be transformed into a highly viscous, colored supramolecular hydrogel with the cross-link density being easily controlled through CB[8] addition. Moreover, the cross-links (1:1:1 supramolecular ternary complexes of CB[8]/viologen/naphthoxy) are dynamic and stimuli-responsive, and the material properties can be modulated by temperature or other external stimuli. Rheological characterization of the bulk material properties of these dynamically cross-linked networks provided insight into the kinetics of CB[8] ternary complexation responsible for elastically active cross-linking with a second guest dissociation rate constant (k(d)) of 1200 s(-1) for the ternary complex. These materials exhibited intermediate mechanical properties at 5 wt % in water (plateau modulus = 350-600 Pa and zero-shear viscosity = 5-55 Pa·s), which is complementary to existing supramolecular hydrogels. Additionally, these supramolecular hydrogels exhibited thermal reversibility and subsequent facile modulation of microstructure upon further addition of CB[8] and thermal treatment. The fundamental knowledge gained from the study of these dynamic materials will facilitate progress in the field of smart, self-healing materials, self-assembled hydrogels, and controlled solution viscosity.
精细调节水基体系溶液粘度的能力在许多应用中至关重要，这些应用范围从大规模基于流体的工业过程到在再生医学、控制药物输送和“绿色”自修复材料中重要的独立水凝胶。在此，我们展示了使用大环主体分子葫芦脲（CB[8]）来促进具有高结合常数（K(a) > 10(11)-10(12) M(-2)）的多价共聚物的可逆交联，从而得到超分子水凝胶。多价共聚物通过自由基聚合技术制备，分别含有侧挂甲基紫精（CB[8]的良好第一客体）或萘氧基衍生物（CB[8]的良好第二客体）。分别带有第一和第二客体的两种多价共聚物的无色溶液可以转变为高度粘稠的有色超分子水凝胶，通过添加 CB[8]可以轻松控制交联密度。此外，交联（CB[8]/紫精/萘氧基的 1:1:1 超分子三元配合物）是动态和对刺激响应的，并且材料性能可以通过温度或其他外部刺激进行调节。这些动态交联网络的体材料性质的流变学特性提供了对 CB[8]三元络合负责具有第二客体离解速率常数（k(d)）为 1200 s(-1)的弹性活性交联的动力学的深入了解三元配合物。这些材料在水中的 5wt%时表现出中等机械性能（平台模量= 350-600 Pa 和零剪切粘度= 5-55 Pa·s），这与现有的超分子水凝胶互补。此外，这些超分子水凝胶表现出热可逆性，并在进一步添加 CB[8]和热处理后可以轻松调节微结构。从这些动态材料的研究中获得的基本知识将促进智能、自修复材料、自组装水凝胶和控制溶液粘度领域的进展。
