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

树枝状聚合物是一种独特的、相对较新的大分子体系，其内部呈指数支化，外部具有密集的官能团，具有许多有利的性质。 树枝状聚合物的内部或外部区域可以用范围从冠醚到氢键键合复合物的特异性结合基团官能化，以选择性地吸附所需的客体系统，并且树枝状聚合物分子中的高密度官能团允许生物底物的高效靶向结合。 树枝状材料系统也被证明可以作为纳米反应器用于形成金属和金属氧化物，以及作为增溶和分离应用中的试剂。 树枝状结构可以针对特定的相互作用或电、光学或生物功能进行定制。 由于这些原因，树枝状聚合物代表了一种独特的大分子系统，具有新颖和有趣的特性。 近年来，一些重要的合成发展导致了具有各种各样的化学和结构性质的新型线性-树枝状杂化嵌段共聚物的产生。 线性-树枝状杂化共聚物提供了利用树枝状聚合物的性质和传统嵌段共聚物的相分离形态自组装的明显机会，其已被证明在溶液中自组装以形成浓缩的溶致相，如层状相和柱状相，以及由球形和圆柱形胶束体系组成的胶束相。 虽然线性嵌段共聚物的两亲性行为已被广泛研究，导致这些系统所呈现的溶致相的理解，还没有一个广泛的研究两亲性的线性-树枝状混合嵌段共聚物，以及它们在溶液中的组装行为。 这是这项工作的目标和智力的优点，进行第一次系统的和包容性的检查线性树枝状嵌段共聚物自组装在溶液状态下，从浓缩到稀释的聚合物溶液，和调查的稳定的纳米结构的材料从这个组件。 高度支化的树枝状嵌段的结构和拓扑结构预计将导致嵌段共聚物界面处的优选曲率的变化，以及这些系统的溶液相行为的变化和转变，如在由先前相关的授予创造性扩展资助的这些系统的本体形态的研究中所观察到的。 线性树枝状嵌段共聚物代表了一种新形式的大分子两亲物，它可能会表现出新的相行为，这项工作将有助于这些大分子两亲物的基本理解，以及在溶液中的组件的生成，线性嵌段长度和溶剂-聚合物相互作用的影响。 这些体系的相行为将为大分子两亲物的研究提供新的范例。与传统的螺旋-螺旋嵌段共聚物的流体动力学半径不同，有可能检查由螺旋和几何约束更大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的自组装树枝状纳米结构，从连续相纳米多孔介质到高功能的树枝状纳米颗粒和其他纳米级物体。 这种线性-树枝状混合嵌段共聚物作为用于形成纳米结构材料和纳米级物体的模板的潜在用途尚未被探索，并且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，将产生含有树枝状外部和线性链内部的胶束系统，并通过交联来稳定，从而产生外部官能度比原始树枝状分子大10至100倍的纳米颗粒。 树枝状嵌段的存在对于许多应用将是有利的，包括产生由溶致相形成的纳米结构多孔材料，其中例如树枝状聚合物端基暴露在纳米孔的内部，所述纳米孔为催化或相互作用孔提供高反应性表面区域。 许多新的和新颖的材料结构可以由功能性线性-树枝状系统的仔细设计和合成产生，所述功能性线性-树枝状系统可以经历交联，促进或支持金属氧化物合成，或用作第二有机材料的模板。 最后，这里所描述的研究是调查员的研究和教学计划的一个组成部分，包括在实验室环境中的本科生和研究生的教育和培训，在本科生和研究生课程的聚合物科学教学中的自组装概念的整合。 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民族学生。 PI的推广包括在剑桥的数学和科学星期六计划中教授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.