Stimuli-responsive hybrid macromolecules: Novel amphiphilic star copolymers with dendritic groups at the periphery
Stimuli-responsive hybrid macromolecules: Novel amphiphilic star copolymers with dendritic groups at the periphery
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DOI：
10.1021/ja9542348
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发表时间：
1996-04-17
影响因子：
15
通讯作者：
Frechet, JMJ
中科院分区：
文献类型：
--
作者：
Gitsov, I;Frechet, JMJ
在这项研究中，我们探索了构建两亲杂化大分子的可能性，该大分子通过改变其形成的胶束类型来响应环境的变化。这些“刺激响应”材料1包含多个附着在星形聚合物末端的树突块，这些树突块可以根据周围介质的变化以不同的方式形成胶束。在这种方法中，中心亲水性聚乙二醇星形臂足够长且柔韧，可以用作间隔物或作为附着在其末端的疏水性树突块的封装“包装物”。应该提到的是，尽管对胶束星2的理论预测和可用合成技术的进步，但之前基本上没有对两亲星和末端功能化星聚合物作为刺激响应大分子的研究。这是因为选择放置在外围的组要么太小，要么太大，无法形成响应外部刺激所需的环路。 2, 3 然而，由于树枝状和 PEG 组分的极性和溶解度存在巨大差异，并且由于位于星体外围的树枝状基团的致密和紧凑结构，因此随着溶剂极性的变化，本研究中描述的系统预计在溶液中采用截然不同的构象。因此，这些不寻常的树状星形聚合物将成为能够响应周围介质变化而形成完全不同类型的单分子胶束的聚合物的第一个例子。几个研究小组现已报道了含有树状聚合物的杂化星状大分子的合成。 4-6 在所有情况下，树突部分都用作星形的核心，以形成具有可预测臂数的结构。尽管有其优点，但这种方法最终产生的传统恒星具有致密、致密的原子核，且具有固定的化学成分和性质。会聚树枝状聚合物7、8的独特反应性在其焦点处具有单个反应基团，使得能够形成具有完全不同结构的混合星，即在外围具有致密和半刚性的树枝状基团。在这项研究中，我们使用著名的 Williamson 醚合成法来形成树枝状嵌段和 PEG 星形之间的连接。 9, 10 偶联反应在室温下顺利进行
In this study we explore the possibility of building an amphiphilic hybrid macromolecule that responds to changes in its environment through changes in the types of micelles it forms. These “stimuli-responsive” materials1 contain multiple dendritic blocks attached to the ends of a star polymer which can micellize differently in response to changes in the surrounding medium. In this approach the central hydrophilic poly-(ethylene glycol) star has arms that are long and flexible enough to serve either as spacers or as encapsulating “wrappers” for the hydrophobic dendritic blocks that are attached to their extremities. It should be mentioned that, in spite of theoretical predictions for micellar stars2 and advances in the synthetic techniques that are available, there are essentially no prior studies of amphiphilic stars and end-functionalized star polymers as stimuli-responsive macromolecules. This is because the groups that had been selected for placement at the periphery were either too small or too large to enable the loop formation that is required as a response to the external stimulus. 2, 3 However, because of the large disparity in the polarity and solubility of the dendritic and PEG components and because of the dense and compact structure of the dendritic groups placed at the periphery of the stars, the systems described in the present study can be expected to adopt vastly different conformations in solution as the solvent polarity is varied. Therefore, these unusual dendritic stars would constitute the first instance of polymers capable of forming totally different types of monomolecular micelles in response to changes in the surrounding medium.The synthesis of hybrid starlike macromolecules containing dendrimers has now been reported by several research groups. 4-6 In all cases the dendritic moiety is used as the core for the star to form structures with a predictable number of arms. In spite of its advantages, this approach ultimately produces traditional stars with dense, compact nuclei that have fixed chemical composition and properties. The unique reactivity of convergent dendrimers7, 8 that possess a single reactive group at their focal points enables the formation of hybrid stars with an entirely different architecture, namely, with the dense and semirigid dendritic groups at the periphery. In this study we use the well-known Williamson ether synthesis to form the link between the dendritic block and the PEG star. 9, 10 The coupling reaction proceeds smoothly at room