Synthesis and physical characterization of arborescent (dendrigraft) polymers

树枝状分子的特征在于具有多个分支水平的结构，类似于树。这些可以细分为三个不同的家庭。树枝状聚合物和超支化聚合物都衍生自ABn型单体（其中官能团A只能与基团B反应; n = 2或3）。树枝状聚合物的完美结构和均匀尺寸来自于严格控制的单体保护、缩合和脱保护反应的循环，但是当缩合反应在没有保护基团的情况下进行时，通常会出现不完美的支化结构和宽尺寸分布。在该提议中感兴趣的树枝状（或树枝状接枝）聚合物通过线性聚合物链段的连续接枝反应获得。这些分子的生长在连续几代（反应循环）中比树枝状聚合物快得多，但它们显示出许多特性;因此，它们是许多纳米技术应用中树枝状聚合物的有趣替代品。本论文主要研究了树状聚合物（AP）的合成及其物理性质。这些都是新材料，因此对它们的结构/组成与性能之间的关系知之甚少。从定义明确的AP系统中获得的信息也将有助于提高对一般支化聚合物系统的理解，其中许多具有商业重要性。* 第一个项目涉及核-壳AP结构，具有疏水多肽核和亲水片段壳。该研究将集中在这些两亲物的增溶和释放性能为不同的模型疏水作为AP分子的结构（分支密度，大小）和组成的函数。这也将提供有关AP分子形态的信息（核和壳之间的相分离程度）。在第二个项目中，将检查由具有核-壳（CS）和核-壳-冠（CSC）结构的AP共聚物形成的金属纳米颗粒，其中含有金属结合的聚（2-乙烯基吡啶）片段。最近，我们观察到形成有趣的nanomorphologies限制在个别AP分子后，引入金属离子。这些纳米结构可能是由于富金属和贫金属区域之间的相互作用（chi）参数存在很大差异而产生的，但它们对这些混合材料的物理化学性质的影响迄今尚未被探索。我们将系统地研究这些纳米结构材料的形成，并最终研究它们的催化性能。CSC系统显示出许多有趣的性质，但它们的合成非常耗时，并且产率低。我们刚刚开始研究合成这些材料的新策略，通过AP核壳结构与嵌段共聚物的自组装，其中一个嵌段可以与AP底物结合。这种方法看起来很有前途，但仍然没有明确的理解规则（热力学）管理这个自组装过程。这些将通过组分结构（例如结合块和AP底物大小）和所用条件（溶剂，温度）的系统变化进行探索。最后，为了继续努力开发合成AP结构的新方法，我们将联合收割机结合我们刚刚开发的“点击”接枝技术与原子转移自由基聚合（ATRP），以显著扩大可获得的树状聚合物组合物的范围。我们还将探索合成具有长侧链的树枝状聚丁二烯结构的方法，因为这些结构作为高度支化的聚合物系统的模型是令人感兴趣的。

Dendritic molecules are characterized by an architecture with multiple branching levels, similar to a tree. These can be subdivided into three distinct families. Dendrimers and hyperbranched polymers are both derived from ABn-type monomers (where functional group A can only react with group B; n = 2 or 3). The perfect structure and uniform size of dendrimers results from strictly controlled cycles of monomer protection, condensation, and deprotection reactions, but an imperfectly branched structure and a broad size distribution often arise when the condensation reaction is carried out without protecting groups. The arborescent (or dendrigraft) polymers, of interest in this proposal, are obtained through successive grafting reactions of linear polymer segments. The growth of these molecules is much faster than for dendrimers over successive generations (reaction cycles), but they display many of their characteristics; they are therefore an interesting alternative to dendrimers for many nanotechnology applications.*This proposal concerns the synthesis and the physical characterization of arborescent polymers (AP). These are novel materials, so there is little understanding of the relationships between their structure/composition and their properties. The information derived from the well-defined AP systems will also help improve the understanding of branched polymer systems in general, many of which are of commercial importance. *The first project involves core-shell AP structures with a hydrophobic polypeptide core and a shell of hydrophilic segments. The research will focus on the solubilization and release properties of these amphiphiles for different model hydrophobes as a function of the structure (branching density, size) and composition of the AP molecules. This will also provide information on the morphology of the AP molecules (extent of phase separation between the core and shell).*In the second project the formation of metallic nanoparticles by AP copolymers with core-shell (CS) and core-shell-corona (CSC) architectures, containing metal-binding poly(2-vinylpyridine) segments, will be examined. We recently observed the formation of intriguing nanomorphologies constrained within the individual AP molecules upon the introduction of metallic ions. These nanostructures likely arise from large differences in interaction (chi) parameter between the metal-rich and metal-poor regions, but their consequences on the physicochemical properties of these hybrid materials are hitherto unexplored. We will examine the formation of these nanostructured materials in a systematic fashion, and ultimately their catalytic properties. The CSC systems display many interesting properties, but their synthesis is very time-consuming and is marred by low yields. We just started investigating a new strategy for the synthesis of these materials, by self-assembly of an AP core-shell structure with a block copolymer where one of the blocks can bind with the AP substrate. This approach looks very promising, but again there is no clear understanding of the rules (thermodynamics) governing this self-assembly process. These will be explored through systematic variations in the structure (e.g. binding block and AP substrate size) of the components and the conditions (solvent, temperature) used.*Finally, to pursue our efforts in developing new methods for the synthesis of AP structures, we will combine a "click" grafting technique which we just developed with atom transfer radical polymerization (ATRP) to considerably expand the range of arborescent polymer compositions available. We will also explore methods for the synthesis or arborescent polybutadiene structures with long side chains, since these are of interest as model highly branched polymer systems.