Understanding the Role of Crystalline Junctions in Associative Polymer Gels

第1部分：非技术概述需要新的策略来制造具有更接近天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Bhatia和Grubbs团队将探索如何将非常小的刚性结构域或纳米级晶体纳入软聚合物凝胶中，从而影响其结构、流动特性和弹性。这些晶体域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、导电聚合物薄膜和热塑性弹性体。PI和Co-PI将培养研究生和本科生广泛的现代高分子材料研究技术，包括合成、化学表征、散射研究和力学表征；他们的目标是为该项目招募代表性不足的学生群体，有利于STEM劳动力的发展，并将不同的学生纳入STEM领域。最后，研究中的例子将被纳入大分子和纳米材料的视频讲座，可用于更新大学水平的核心化学课程，并作为K-6学生的示范。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输运性。在这个项目中，石溪大学的Bhatia和Grubbs小组将探索立体化学和结晶度对缔合嵌段共聚物凝胶的流变性和纳米到微观结构的影响。尽管结晶度长期以来一直被用作控制聚合物在固体状态下性能的一种手段，但对具有结晶域的溶液和凝胶的研究一直受到限制。理解这些系统的物理性质的一个主要挑战是在多相系统中量化有序，这些多相系统包含无定形和有序畴，其中有序畴太小，无法通过传统的衍射方法轻松识别。研究人员将利用x射线对分布分析（PDF）来量化这些材料中的链顺序，从而克服这一问题。该项目将重点研究选择性溶剂中的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）。总体目标是在选择性溶剂中建立具有可结晶嵌段的嵌段共聚物的基本，全面的结构-性能关系。具体目标是：(1)合成一系列具有不同PLA和PEO嵌段长度和L/D比的PLA-PEO-PLA三嵌段聚合物；(2)使用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)测量凝胶的流变特性，并将其与现有的聚合物网络模型进行比较；(4)将研究实例整合到本科和研究生的化学核心课程中，并为K-6学生提供示范。该奖项反映了美国国家科学基金会的法定使命，并通过基金会的智力价值和更广泛的影响评估标准进行了评估，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.