Divergent synthesis of dendronized poly(p-hydroxystyrene)
Divergent synthesis of dendronized poly(p-hydroxystyrene)
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DOI：
10.1021/ma010698g
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发表时间：
2001-09-11
期刊：
影响因子：
5.5
通讯作者：
Fréchet, JMJ
中科院分区：
文献类型：
--
作者：
Grayson, SM;Fréchet, JMJ
导论.根据Schlüter的定义，树枝化聚合物1、2是沿着主链沿着具有悬垂树枝状分子的线性聚合物。由于空间上的考虑，具有可观聚合度（DP）的高代树枝化聚合物的合成已被证明具有挑战性。大多数试图获得这种结构的尝试都利用了大分子单体方法3，在聚合之前将所需的树枝化基元连接到单体单元上。已经研究了各种各样的聚合技术，2包括自由基聚合、开环易位聚合、Heck或Stille偶联和Suzuki缩聚。虽然这种大分子单体方法确保每个单体单元携带结构上纯的树枝化基元，但高代树枝化基元的空间拥挤可能会掩盖反应位点，导致材料具有低聚合度和高多分散性。2，4另一种方法需要在聚合后将预形成的会聚树枝化基元附着到线性聚合物上。这种方法能够更好地控制线性主链的长度和分散性，但存在空间复杂性，因为在更高的世代，树枝化基元连接到重复单元的悬垂官能团上可能阻碍相邻的偶联位点，从而阻止完全树枝化。可以证明对于通过引发从预形成的聚合物的每个重复单元上的悬垂位点的生长来制备树枝化聚合物是有价值的。通过在更容易接近的外周上进行树枝状偶联反应，空间复杂性应最小化。然而，很明显，该方法只能在非常清洁的化学过程中使用，没有环化或其他副反应，才能充分受益。Tomalia及其同事在十多年前首次声称树枝化聚合物的发散性生长; 6然而，由于缺乏已发表的数据和表征产品结构的明显困难，该过程并未引起太多关注。虽然这些材料的隧道电子显微镜研究7发表于1998年，这些材料的详细表征还没有被报道，使得分散制备的材料的结构完整性难以评估。在这里，我们报告的分歧接枝脂肪族聚酯树枝状分子从聚（对羟基苯乙烯）的核心。用基质辅助激光解吸电离飞行时间质谱（TOF MS）对聚合物进行了表征
Introduction. As defined by Schlüter, dendronized polymers1, 2 are linear polymers that bear pendant dendrons along the backbone. The synthesis of high generation dendronized polymers with an appreciable degree of polymerization (DP) has proven challenging because of steric considerations. The majority of the attempts to access this architecture have utilized the macromonomer approach3 attaching the desired dendron to the monomer unit before polymerization. A wide variety of polymerization techniques have been investigated, 2 including radical polymerization, ring-opening metathesis polymerization, Heck or Stille coupling, and Suzuki polycondensation. Although this macromonomer approach ensures that each monomer unit carries a structurally pure dendron, the steric crowding of high generation dendrons can obscure the reactive site, leading to materials with low degrees of polymerization and high polydispersities. 2, 4 An alternative approach entails the attachment of preformed convergent dendrons to a linear polymer after polymerization. This approach enables greater control over the length and dispersity of the linear backbone but suffers from steric complications because, at higher generations, the attachment of dendrons onto the pendant functionalities of the repeat units can hinder neighboring coupling sites, preventing complete dendronization.The divergent growth approach, 5 though also subject to steric limitations, may prove valuable to prepare dendronized polymers by initiating growth from pendant sites on each repeat unit of a preformed polymer. By carrying out the dendritic coupling reactions on the more accessible periphery, steric complications should be minimized. It is clear however that the method can only be used to full benefit if exceptionally clean chemistry, free of cyclization or other side reactions, is available. Tomalia and co-workers first claimed the divergent growth of dendronized polymers over a decade ago; 6 however, this procedure has not attracted much attention because of the lack of published data and apparent difficulties in characterizing the structure of the product. Although tunneling electron microscopy studies7 of these materials were published in 1998, the detailed characterization of these materials has yet to be reported, making the structural integrity of divergently prepared materials difficult to evaluate. Herein, we report the divergent grafting of aliphatic polyester dendrons from a poly (p-hydroxystyrene) core. The resulting polymers were characterized by matrixassisted laser desorption ionization time-of-flight mass