Understanding the Role of Crystalline Junctions in Associative Polymer Gels

第一部分： 非技术总结需要新的策略来制造具有更接近天然材料的机械和结构特性的聚合物。在这个项目中，斯托尼布鲁克大学的Bhatia和Grubbs小组将探索如何将非常小的刚性域或纳米级微晶包含到软聚合物凝胶中，从而影响它们的结构、流动特性和弹性。这些结晶域代表了一种新的方法，用于控制聚合物凝胶的结构和机械性能。 因此，这项工作将影响改进材料的设计，以促进国家健康和繁荣，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将为研究生和本科生提供现代聚合物材料研究的广泛技术培训，包括合成，化学表征，散射研究和机械表征;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劳动力发展和STEM领域的多元化学生。最后，从研究的例子将被纳入视频讲座的大分子和纳米材料，可用于更新核心化学课程在大学一级，并进入演示K-6学生。 第二部分： 技术概述这项工作集中在控制水凝胶的纳米结构和微结构，同时保持所需的流变和传输性能。在这个项目中，斯托尼布鲁克大学的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学和纳米到微米尺度结构的影响。尽管结晶度长期以来一直被用作控制固态聚合物性质的手段，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学的一个主要挑战是量化包含无定形和有序域的多相系统中的有序性，其中有序域太小而不能通过常规衍射方法容易地辨别。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序来克服这一问题。该项目将集中在阿坝三嵌段共聚物在选择性溶剂中，其中中间嵌段是聚（环氧乙烷）（PEO）和端嵌段是聚（乳酸）（PLA）。总体目标是建立基本的，全面的结构与性能的关系，在选择性溶剂中的结晶嵌段的嵌段共聚物。具体目标是：（1）合成了一系列具有不同PLA和PEO嵌段长度和长径比的PLA-PEO-PLA三嵌段聚合物;（2）用DLS、SAXS/SANS、PDF、USANS和共聚焦显微镜表征了这些聚合物的结构、组装和结晶性;（3）测量了凝胶的流变性能并将其与现有的聚合物网络模型进行了比较;以及（4）将研究中的实例整合到本科生和研究生的化学核心课程中，并为K-6观众进行演示。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

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.