CAREER: Stimuli-Responsive Dynamic Macromolecular Assemblies

技术概述：这项研究利用二元醇和硼酸之间形成可逆键的强健性质，用于制备和研究自组装和响应性大分子材料。将研究两个特殊的系统：(1)刺激响应型嵌段共聚聚合物组件和(2)动态共价自组装材料。在第一个体系中，通过控制自由基聚合和其他有效的后聚合转化，将合成具有永久亲水嵌段(例如，聚乙二醇或聚丙烯酰胺)和含有丙烯酰胺或苯乙烯嵌段的响应性硼酸的两嵌段共聚物。在没有二元醇的情况下，在硼酸部分的pHpKa下，有机硼链段将脱水和不溶，导致两亲性嵌段共聚物自组装成胶束和囊泡。二醇的引入将导致硼酸的pKa降低，由此形成的阴离子硼酸酯将导致溶解度转变和聚集体解体。研究将阐明诱导聚集体解离所需的临界二元醇浓度、pH和温度，并将深入了解控制组装和解离的动力学。第二类材料依赖于硼酸-二醇酯化反应，通过自组装具有端基或侧链二元醇和硼酸官能团的(Co)聚合物来构建共价大分子结构。分子刷、星形和其他支链拓扑结构将通过在主体状态和有机或水溶液中形成硼酸酯或硼酸酯来构建。硼酸酯的水解将导致拓扑结构复杂的大分子可逆地解离成单独的线性聚合物组分。在可逆共价体系固有的平衡条件下，引入第二个含二元醇的聚合物，形成更稳定的硼酸酯络合物，将导致大分子构建基团的交换。有效交换所需的选择性将通过设计具有截然不同的络合电位的聚合物来实现。因此，在大分子解离后，在存在竞争平衡的情况下进行重构将导致交换聚合物构建块来产生新材料。通过组装-拆卸来重新洗牌成分的能力也将被用来在溶液中诱导戏剧性的架构重新排列(例如，刷子到星形的转变)。这项研究试图重新定义刺激响应性聚合物的传统概念，以包括随着环境压力而改变其化学功能和整体链拓扑结构的大分子结构。非技术摘要：通过制备当暴露于局部环境变化时经历破裂和重建的纳米级物体，可以从根本上洞察许多控制治疗药物输送的机制以及新的自我修复和适应材料的行为。由于这些研究需要材料科学、化学和工程学的各种技能，参与这项研究的学生和初级科学家获得了一套真正的跨学科技能，这些技能可以增强加快新的先进和特殊材料市场发展所需的劳动力。这项研究的一个外联部分旨在通过与当地社区学院和独立的K-12学区建立合作关系，直接解决美国竞争力倡议的许多任务，以促进将代表不足的少数族裔学生纳入南卫理公会大学化学系的实习职位。

TECHNICAL SUMMARY:This research capitalizes on the robust nature of reversible bond formation between diols and boronic acids for the preparation and investigation of self-assembled and responsive macromolecular material. Two particular systems will be investigated: (1)stimuli-responsive block copolymer assemblies and (2)dynamic covalent self-assembled materials. In the first system, diblock copolymers with a permanently hydrophilic block (e.g.,poly(ethylene glycol) or polyacrylamide) and a responsibe boronic acid containing acrylamido or styrenic block will be prepared by combination of controlled radical polymerization and other efficient postpolymerization transformations. In the absence of diol and at pHpKa of the boronic acid moieties, the organoboron segments will be dehydrated and insoluble, leading to self-assembly of the amphiphilic block copolymers into micelles and vesicles. Introduction of diols will lead to a reduced pKa of the boronic acids, and the resulting anionic boronate ester formation will cause a solubility transition and aggregate disassembly. Investigations will elucidate the critical diol concentration, pH, and temperature necessary to induce aggregate dissociation, and insight will be gained into the kinetics governing assembly and sissociation. The second class of materials relies on boronic acid-diol esterification to construct covalent macromolecular architectures via self-asembly of (co)polymers with either terminal or pendant diol and boronic acid functionality. Molecular brushes, stars, and other branched chain topologies will be constructed via boronic or boronate ester formation in the bulk state and in organic or aqueous solutions. Hydrolysis of the boronate esters will lead to reversible dissociation of the topologically complex macromolecules into individual linear polymer components. Under the equilibrium conditions inherent to reversible covalent systems, introduction of a second diol-containing polymer that forms a more stable boronate ester complex will lead to an exchange of macromolecular building blocks. The selectivity requred for efficient exchange will be implemented by designing polymers with dramatically different complexation potentioals. Thus, after macromolecular dissociation, reconstruction in the presence of a competing equilibrium will result in exchange of polymer building blocks to yield a new materials. The ability to reshuffle constituents through assembly-disassembly will also be employed to induce dramatic architectural rearrangements in solution (e.g., brush to star transitions). This research seeks to redefine the traditional concept of stimuli-responsive polymers to include macromolecular constructs that change both their chemical functionality and overall chain topology in response to environmental stress.NON-TECHNICAL SUMMARY:By preparing nanoscale objects that undergo rupture and reconstruction when exposed to changes in their local environment, fundamental insight can be gained into many of the mechanisms governing the controlled delivery of therapeutics and the behavior of new self-healing and adaptive materials. Because these studies require a diverse set of skills from materials science, chemistry, and engineering, students and junior scientists involved in this research are provided with a truly interdisciplinary set of skills that can enhance the workforce necessary to accelerate development of new advanced and sepciality materials market. An outreach component of the research is desinged to directly address many of the mandates of the American Competitiveness Initiative by establishing collaborations with local community colleges and independent K-12 school districts to facilitate the inclusion of underrepresented minority students for internship positions within the Department of Chemistry at Southern Methodist University.