Understanding the Role of Crystalline Junctions in Associative Polymer Gels

第1部分：非技术总结需要新的策略来创造具有更接近自然材料的机械和结构性能的聚合物。在这个项目中，石溪大学的巴提亚和格拉布斯小组将探索在软聚合物凝胶中加入非常小的刚性结构域或纳米微晶对其结构、流动特性和弹性的影响。这些晶区代表了一种控制聚合物凝胶结构和力学性能的新方法。因此，这项工作将影响改进材料的设计，用于促进国家健康和繁荣的应用，包括软组织工程和药物输送。该项目还将有助于开发新的实验技术，以表征同时包含有序和无序结构域的聚合物材料，如生物聚合物凝胶、导电聚合物膜和热塑性弹性体。PI和Co-PI将在现代聚合物材料研究的广泛技术方面培训研究生和本科生，包括合成、化学表征、分散研究和机械表征；他们的目标是为这个项目招收代表不足的学生群体，有利于STEM劳动力的发展和STEM领域的不同学生。最后，研究中的例子将被纳入关于大分子和纳米材料的视频讲座，可用于更新大学一级的核心化学课程，并成为K-6学生的演示。第二部分：技术总结这项工作的重点是控制水凝胶的纳米结构和微观结构，同时保持所需的流变性和传输性能。在这个项目中，石溪大学的巴蒂亚和格拉布斯小组将探索立体化学和结晶度对缔合嵌段共聚凝胶的流变学和纳米到微米尺度结构的影响。虽然结晶度长期以来一直被用作控制固态聚合物性能的一种手段，但对具有结晶区的溶液和凝胶的研究一直很有限。要理解这些系统的物理性质，一个主要的挑战是量化多相系统中的有序性，这些多相系统同时包含无定形和有序结构域，其中有序结构域太小，无法通过传统的衍射方法容易地识别。研究人员将通过利用X射线对分布分析(PDF)来量化这些材料中的链排序来克服这一点。该项目将重点放在选择性溶剂中的ABA三嵌段共聚物，其中中间嵌段为聚环氧乙烷(PEO)，末端嵌段为聚乳酸(PLA)。总的目标是为在选择性溶剂中具有可结晶嵌段的嵌段共聚物建立基本的、全面的结构-性能关系。具体目标是：(1)合成一系列具有不同聚乳酸和聚氧乙烯嵌段长度和L/D比的聚乳酸-聚氧乙烯-聚乳酸三嵌段聚合物；(2)用DLS、SAXS/SANS、PDF、USANS和共聚焦显微镜表征这些聚合物的结构、组装和结晶度；(3)测量凝胶的流变性，并与现有的聚合物网络模型进行比较；以及(4)将研究中的例子整合到本科生和研究生的化学核心课程中，并为K-6受众提供示范。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYNew strategies are needed to create polymers with mechanical and structural properties that more closely mimic natural materials. In this project, the Bhatia and Grubbs groups at Stony Brook University will explore how including very small rigid domains, or nanoscale crystallites, into soft polymer gels impacts their structure, flow properties, and elasticity. These crystalline domains represent a novel method for controlling the structural and mechanical properties of polymer gels. Thus, the work will impact design of improved materials for applications that contribute to national health and prosperity, including soft tissue engineering and drug delivery. The project will also contribute to the development of new experimental techniques to characterize polymeric materials that contain both ordered and disordered domains such as biopolymer gels, conductive polymer films, and thermoplastic elastomers. The PI and Co-PI will train graduate and undergraduate students in a wide range of techniques for modern polymer materials research, including synthesis, chemical characterization, scattering studies, and mechanical characterization; and they will aim to recruit under-represented student populations for this project, benefiting STEM workforce development and inclusion of diverse students in STEM fields. Finally, examples from the research will be incorporated into video lectures on macromolecules and nanomaterials that can be used to update the core chemistry curricula at the college level and into demonstrations for K-6 students. PART 2: TECHNICAL SUMMARYThis work is focused on control of hydrogel nanostructure and microstructure while maintaining desired rheological and transport properties. In this project, the Bhatia and Grubbs groups at Stony Brook University will explore the impact of stereochemistry and crystallinity on the rheology and nano- to micro-scale structure of associative block copolymer gels. Although crystallinity has long been used as a means of controlling polymer properties in the solid state, studies of solutions and gels with crystalline domains have been limited. A major challenge in understanding the physics of these systems is quantifying ordering in multiphase systems that contain both amorphous and ordered domains, where the ordered domains are too small to easily discern through conventional diffraction methods. The researchers will overcome this by utilizing X-ray pair distribution analysis (PDF) to quantify chain ordering in these materials. The project will focus on ABA triblock copolymers in a selective solvent, where the midblock is poly(ethylene oxide) (PEO) and the endblocks are poly(lactic acid) (PLA). The overall goal is to build fundamental, comprehensive structure-property relationships for block copolymers with crystallizable blocks in selective solvents. Specific objectives are to: (1) Synthesize a series of PLA-PEO-PLA triblock polymers with varying PLA and PEO block length and L/D ratio; (2) Characterize the structure, assembly, and crystallinity of these polymers using DLS, SAXS/SANS, PDF, USANS, and confocal microscopy; (3) Measure the rheological properties of the gels and compare these to existing models of polymer networks; and (4) Integrate examples from the research into undergraduate and graduate core courses in chemistry and demonstrations for K-6 audiences..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.