Viscoelastic Behavior of Stimuli-Responsive Metallo-Supramolecular Polymers

刺激响应性聚合物（Stimuli-responsive polymers，SRPs）在受到外界刺激时，如温度、离子强度、pH值、电场、磁场、机械场或化学或生物分析物等的变化，其性质会发生变化。实例包括液晶聚合物（LCP）、聚合物溶液和凝胶（其经历相形态的变化）、电流变和磁流变流体以及电活性聚合物（EAP）。SRPs作为智能薄膜在传感器、执行器、电光器件等方面具有潜在的应用前景，其中粘弹性变得重要。最近的一个进展是基于金属与配体结合的金属超分子聚合物和网络的发展。该项目要求支持研究一类新型金属超分子聚合物的粘弹性行为的分子起源。J. Rowan和同事，它溶解在各种有机溶剂中，并且可以通过掺入光子或离子传导部分而方便地官能化。这些材料的粘弹性和热力学行为的分子起源的知识是走向合理的分子设计的关键一步，旨在优化它们的性能，并了解如何将它们加工成功能膜。迄今为止，尚未系统地开展这类研究，而这类研究正是本提案的主题。 Rowan等人通过添加镧系元素和过渡金属离子（分别作为交联剂和扩链剂），从双配体官能化单体中创建了超分子聚合物和受控结构网络。因此，分子量和网络结构由离子浓度和组成以及离子结合强度和动力学决定。这些材料将金属离子的功能性与动态聚合物网络的可加工性和机械强度相结合。我们提出的研究，首先调查的超分子polymersformed通过混合单体与过渡金属离子的性质。粘度，光散射和小角中子散射研究将作为一个功能的单体：金属离子比，在不同的溶剂，并作为一个功能的温度。探讨了金属离子与溶剂的配位力在反应中的作用。在平衡链和/或动力学冻结链理论的背景下，结果将被解释为表观链分子量。这些研究将扩展到研究添加镧系元素作为交联剂的影响。凝胶化和/或相分离的发生将通过散射和流变测量来探测。凝胶相的结构和形态将通过光、X射线和中子散射技术以及光学和透射电子显微镜进行检查。这些研究将为这类重要的新型刺激响应材料提供前体结构和金属离子结合特性与热力学和粘弹性行为之间关系的第一个全面的图片。 该提案的智力价值来自于这样一个事实，即所获得的结果将产生关于一类重要的新的刺激响应材料的重要的新的基础知识。此外，它们将用于测试现有的自组装聚合物和网络的理论，更重要的是，预计将发现新的现象，这将为理论家提供新的挑战。 此外，该项目将产生更广泛的影响，因为它将培养两名博士研究生，并有望为本科生提供研究机会，在聚合物研究的一个重要领域。研究结果将在国家和国际会议上传播，并将在主要科学期刊上发表。此外，预计我们的研究结果将产生药理学知识，这将是这些材料作为功能性，刺激响应涂层和薄膜的实际商业应用的重要一步。

Stimuli-responsive polymers (SRPs) exhibit a change in properties upon application of an externalstimulus, such as a change in temperature, ionic strength, pH, electric, magnetic or mechanical fields or bychemical or biological analytes. Examples include liquid crystal polymers (LCPs), polymer solutions andgels, which undergo a change in phase morphology, electro- and magnetorheological fluids and electroactivepolymers (EAPs). SRPs have potential applications as smart films in sensors, actuators, electro-opticdevices, etc., where the viscoelastic properties become important. A recent advance has been thedevelopment of metallosupramolecular polymers and networks based on metal:ligand binding. This projectrequests support to investigate the molecular origin of the viscoelastic behavior of a novel family ofmetallosupramolecular polymers, developed by S. J. Rowan and coworkers, which dissolve in variousorganic solvents, and which can be conveniently functionalized by incorporation of photonic or ionconductingmoieties. Knowledge of the molecular origin of the viscoelastic and thermodynamic behavior ofthese materials is a key step towards rational molecular design, aimed at optimizing their properties, and tounderstanding how to process them into functional films. Such studies have not been systematicallypursued to date, and are the subject of this proposal. Rowan et al. create supramolecular polymers and networks of controlled architectures from a bisligandfunctionalized monomer via addition of lanthanide and transition metal ions, which act, respectively,as crosslinkers and as chain extenders. Thus, the molecular weight and network architecture is determinedby the ionic concentration and composition, and by the ion-binding strength and kinetics. These materialscombine the functionality of the metal ions with the processability and mechanical strength of a dynamicpolymeric network. We propose studies to first investigate the properties of the supramolecular polymersformed by mixing the monomer with transition metal ions. Viscometric, light scattering and small-angleneutron scattering studies will be performed as a function of monomer:metal ion ratio, in different solvents,and as a function of temperature. The role of the coordinating power of the metal ion and solvent will beexplored. The results will be interpreted in terms of apparent chain molecular weight, in the context oftheories of equilibrium chains and/or kinetically frozen chains. These studies will then be extended to studythe effects of adding lanthanide as crosslinker. The onset of gelation and/or phase separation will be probedby scattering and rheological measurements. The structure and morphology of the gel phase will beexamined by light, x-ray and neutron scattering techniques and by optical and transmission electronmicroscopy. These studies will provide the first comprehensive picture of the relationship betweenprecursor structure and metal ion binding characteristics versus thermodynamic and viscoelastic behaviorfor this important new class of stimuli-responsive materials. The intellectual merit of the proposal derives from the fact that the results obtained will generateimportant new fundamental knowledge on an important new class of stimuli-responsive materials. Inaddition, they will serve to test existing theories of self-assembling polymers and networks, and moreimportantly are expected to identify novel phenomena, which will provide new challenges for theorists. Moreover, the project will have broader impact, in that it will serve to train two PhD graduatestudents, and is expected to provide research opportunities for undergraduate students in a vital area ofpolymer research. The results will be disseminated at national and international meetings and will bepublished in leading scientific journals. In addition, it is expected that our findings will generate empiricalknowledge, which will be an important step toward practical commercial application of these materials asfunctional, stimuli-responsive coatings and films.