Viscoelastic Behavior of Stimuli-Responsive Metallo-Supramolecular Polymers

刺激响应型聚合物(SRP)在施加外界刺激时，如温度、离子强度、pH、电场、磁场或机械场的变化或化学或生物分析物的变化，其性质会发生变化。例子包括液晶聚合物(LCP)，聚合物溶液和凝胶，它们经历了相形态的变化，电和磁流变液和电活性聚合物(EAP)。SRPS作为智能薄膜在传感器、执行器、电光器件等领域具有潜在的应用前景，其中粘弹性性能变得非常重要。金属超分子聚合物和金属网络的最新进展是：配体结合。该项目要求研究由S.J.Rowan及其同事开发的一类新型金属超分子聚合物粘弹行为的分子起源，这种聚合物可溶于各种有机溶剂，并可通过结合光子或离子导电部分方便地功能化。了解这些材料的粘弹性和热力学行为的分子起源是进行合理的分子设计的关键一步，目的是优化它们的性能，并了解如何将它们加工成功能薄膜。到目前为止，这类研究还没有得到系统的反对，而且是本提案的主题。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)，从双链和官能化单体中创建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网络的加工性和机械强度结合在一起。我们建议首先研究由单体与过渡金属离子混合形成的超分子聚合物的性质。粘度计、光散射和小角中子散射的研究将作为单体与金属离子比例的函数、在不同的溶剂中以及作为温度的函数进行。探讨了金属离子与溶剂配位力的作用。结果将在平衡链和/或动力学冻结链理论的背景下，用表观链分子量来解释。然后，这些研究将扩展到研究添加稀土元素作为交联剂的效果。胶凝和/或相分离的开始将通过散射和流变学测量来探测。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的前驱体结构和金属离子结合特性与热力学和粘弹性行为之间的关系提供第一个全面的图景。该提议的学术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，它们将用于检验现有的自组装聚合物和网络理论，更重要的是有望发现新的现象，这将给理论家带来新的挑战。此外，该项目将产生更广泛的影响，因为它将培养两名博士生，并有望为本科生提供一个重要的聚合物研究领域的研究机会。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，预计我们的发现将产生经验性知识，这将是这些材料作为功能、刺激响应性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.