Exploring the Concentrated Lyotropic and Dilute Solution Assembly of Linear-Dendritic Block Copolymers

树枝状大分子是一种独特的、相对较新的大分子体系，其内部呈指数级分支的内部和密集的外部官能团提供了许多有利的性质。树枝状大分子的内部或外部区域可以通过特定的结合基团来功能化，从冠醚到氢键络合物，以选择性地吸附所需的客体体系，并且树枝状大分子分子中高密度的官能团允许高效地靶向结合生物底物。树枝状材料系统还被证明是金属和金属氧化物形成的纳米反应器，以及在增溶和分离应用中的试剂。树枝状结构可以为特定的相互作用或电、光或生物功能量身定做。由于这些原因，树枝状大分子代表着一种独特的大分子体系，具有新颖而有趣的性质。近年来，一些重要的合成进展催生了具有各种化学性质和结构性质的新型线状-树枝状杂化嵌段共聚物。线状-树枝状杂化共聚物提供了一个很好的机会来利用树枝状大分子的性质和传统嵌段共聚物的相分离形态自组装，这些嵌段共聚物在溶液中自组装形成集中的溶致相，如片状和柱状相，以及由球形和柱状胶束体系组成的胶束相。虽然线型嵌段共聚物的两亲性行为已经被广泛地研究，从而使人们对这些体系所呈现的溶致相有了更多的了解，但对于两亲性线型-树枝状杂化嵌段共聚物及其在溶液中的组装行为还没有广泛的研究。这项工作的目标和智力价值在于首次系统和全面地考察了线状-树枝状嵌段共聚物在溶液状态下(从浓到稀)的自组装，并研究了由这种组装产生的稳定的纳米结构材料。高度支化的树枝状嵌段的结构和拓扑预计会导致嵌段共聚物界面处优先曲率的变化，以及这些体系的溶液相行为的变化和移动，正如在由以前的相关赠款创造力扩展资助的对这些体系的整体形态的研究中所观察到的那样。线状-树枝状嵌段共聚物代表了一种新的大分子两亲性，它可能表现出新的相行为；这项工作将有助于从根本上理解这些大分子两亲性，以及生成量、线状嵌段长度和溶剂-聚合物相互作用对溶液组装的影响。预计这些体系的相行为将为大分子两亲化合物领域引入一种新的范式。与传统的线圈-线圈嵌段共聚物的流体力学半径不同，可以检查由线圈和几何约束程度更高的聚合物嵌段组成的嵌段的排列。这项研究的更广泛的影响包括创造新型的自组装树枝状纳米结构，范围从连续相纳米多孔介质到高功能树枝状纳米颗粒和其他纳米级物体。这种线状-树枝状杂化嵌段共聚物作为模板形成纳米结构材料和纳米级物体的潜在用途仍有待探索，预计将影响纳米结构材料系统的设计。利用两亲性嵌段共聚物组装的原理，将创建包含树枝状外部和直线链内部的胶束体系，并通过交联来稳定胶束体系，从而产生表面官能度是原始树枝状的10到100倍的纳米粒子。树枝状嵌段的存在将有利于许多应用，包括创建由溶致相形成的纳米结构多孔材料，其中，例如，树枝状大分子端基暴露在为催化或交互作用的孔提供高活性表面区的纳米孔的内部。许多新的和新颖的材料结构可以通过精心设计和合成功能性的线状-树枝状系统而产生，这些功能线状-树枝状系统可以进行交联，鼓励或支持金属氧化物的合成，或者作为第二种有机材料的模板。最后，本文描述的研究是研究者研究和教学计划的组成部分，包括在实验室环境中对本科生和研究生的教育和培训，将自组装概念整合到本科生和研究生课程的聚合物科学教学中。对学生的辅导涉及各个层面，包括学术和职业问题、工作和家庭问题，其中包括一些妇女和少数族裔学生。PI的外展活动包括在剑桥的数学和科学星期六项目中教授9-12岁的学生。

Dendrimers are unique and relatively new macromolecular systems whose exponentially branched interiors and dense exterior functional groups offer a number of advantageous properties. The interior or exterior regions of dendrimers can be functionalized with specific binding groups, ranging from crown ethers to hydrogen bonded complexes, to selectively adsorb a desired guest system, and the high density of functional groups in the dendrimer molecule allows for highly efficient targeted binding of biological substrates. Dendritic materials systems have also been shown to act as nanoreactors for the formation of metals and metal oxides, and as agents in solubilization and separations applications. Dendritic architectures can be tailored for specific interactions, or for electrical, optical or biological functionality. For these reasons, dendrimers represent a unique macromolecular system with novel and interesting properties. In recent years, a number of important synthetic developments have led to the creation of novel linear-dendritic hybrid block copolymers with a wide variety of chemical and structural properties. Linear-dendritic hybrid copolymers offer a clear opportunity to take advantage of the properties of dendrimers and the phase segregated morphological self-assembly of traditional block copolymers, which have been shown to self-assemble in solution to form concentrated lyotropic phases such as lamellae and columnar phases, and micellar phases consisting of spherical and cylindrical micellar systems. Although the amphiphilic behavior of linear block copolymers has been studied extensively, resulting in an understanding of the lyotropic phases presented by these systems, there has not been an extensive study of amphiphilic linear-dendritic hybrid block copolymers, and their assembly behavior in solution. It is the objective and intellectual merit of this work to undertake the first systematic and inclusive examination of linear-dendritic block copolymer self-assembly in the solution state, from concentrated to dilute polymer solution, and the investigation of the stabilized nanostructured materials resulting from this assembly. The architecture and topology of the highly branched dendritic block is expected to lead to changes in the preferred curvature at the block copolymer interface, and variations and shifts in the solution phase behavior of these systems, as has been observed in studies of the bulk morphology of these systems in funded by the previoius related grant creativity extension. Linear-dendritic block copolymers represent a new form of macromolecular amphiphile which may exhibit novel phase behavior; this work will contribute significantly to a fundamental understanding of these macroamphiphiles, and the effects of generation, linear block length and solvent-polymer interactions on the assembly in solution. It is anticipated that the phase behavior of these systems will introduce a new paradigm to the area of macromolecular amphiphiles . rather than the traditional hydrodynamic radius of a coil-coil block copolymer, it is possible to examine the arrangement of a block consisting of the coil and a much more geometrically constrained polymer block. The broader impacts of this study include the creation of novel self-assembled dendritic nanostructures ranging from continuous phase nanoporous media to highly functional dendritic nanoparticles and other nanoscale objects. The potential use of such linear-dendritic hybrid block copolymers as templates for the formation of nanostructured materials and nanoscale objects is yet to be explored, and is expected to impact the design of nanostructured materials systems. Utilizing the principles of amphiphilic block copolymer assembly, micellar systems containing dendritic exteriors and linear chain interiors will be created and stabilized with crosslinking, resulting in nanoparticles for which the exterior functionality is 10 to 100 times greater than that of the original dendron. The presence of the dendritic block will be advantageous for a number of applications, including the creation of nanostructured porous materials formed from the lyotropic phase in which, for example, the dendrimer end groups are exposed within the interiors of nanopores that provide a highly reactive surface region for catalytic or interactive pores. A number of new and novel materials structures can result from the careful design and synthesis of functional linear-dendritic systems which may undergo crosslinking, encourage or support metal oxide synthesis, or serve as a template for a second organic material. Finally, the research described here is an integral part of the investigator's research and teaching plan, and includes the education and training of undergraduate and graduate students in the laboratory environment, the integration of concepts of self-assembly in the teaching of polymer science in under-graduate and graduate courses. The mentorship of students takes place on every level, including academic and career issues, work and family concerns, and includes a number of women and minority students. Outreach of the PI includes teaching of students aged 9-12 in a Math and Science Saturday Program in Cambridge.