Chiral hyperbranched dendron analogues
Chiral hyperbranched dendron analogues
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DOI：
10.1021/ma9915881
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发表时间：
2000-01-25
期刊：
影响因子：
5.5
通讯作者：
Frey, H
中科院分区：
文献类型：
--
作者：
Sunder, A;Mülhaupt, R;Frey, H
树枝状大分子是一种以ABm型结构单元为基础的完全级联支化的大分子，具有大量的端基。1树枝状体是树枝状聚合物“楔形物”，其特征在于在核心处恰好存在一个官能团，其不同于结构外围中的B端基。最近，树枝状结构已被广泛用作制备“树枝化”聚合物的通用模块。[2]在大多数用作超分子结构单元的树枝状基元的例子中，都使用了Hawker和Fréchet基于收敛反应开发的树枝状聚苄基醚。3通常，由于它们的锥形或圆锥形，树枝状分子可用于创建形状控制的纳米结构和纳米物体。4树枝状大分子化学中的一个重要问题是将手性单元引入级联支化结构中。这可以通过合适的端基官能化或通过使用手性结构单元来实现。6，7然而，迄今为止，只有几个例子的手性树突已被报道。8，9与冗长的树枝状聚合物相比，超支化聚合物是由ABm型或潜在ABm型单体一锅合成的级联支化结构。因此，它们的结构不太完美地分支;即，线性、树枝状和末端单元随机并入。与树枝状聚合物相比，超支化聚合物不具有结构密度梯度。到目前为止，超支化聚合物一直被认为是定义不明确的，因为它们通常具有广泛的多分散性和缺乏对核掺入的控制。最近，我们报道了基于缩水甘油的开环多支化聚合（ROMBP）制备高度限定的超支化聚甘油。11由于该方法的链增长性质，这些大分子具有用作核心单元的引发剂，并且可以在1000和10 000之间的分子量范围内制备，具有窄的多分散性Mw/Mn< 1.5（大部分< 1.3）。分子量由单体/引发剂比率控制。在这篇通讯中，我们报告了手性超支化聚合物和手性超支化树枝化类似物1的首次合成，基于两种市售缩水甘油对映体的聚合（方案1）。通过带有官能团（即末端双键）的引发剂在核心处精确地引入一个官能团。手性聚甘油通常可适用于对映异构体的分离、手性催化或生物化学应用。连接到树枝状结构中的焦点单元的单个双键可用于通过普通烯烃反应的各种进一步官能化方法，
Dendrimers are perfectly cascade-branched macromolecules based on ABm type structural units, possessing a large number of end groups. 1 Dendrons are dendrimer “wedges”, which are characterized by the presence of precisely one functional group at the core, which is different from the B end groups in the periphery of the structure. Recently, dendron structures have been used widely as versatile modules for the preparation of “dendronized” polymers. 2 In most examples of dendrons used as supramolecular building blocks, dendritic polybenzyl ethers based on convergent reactions developed by Hawker and Fréchet have been employed. 3 Generally, due to their tapered or conical shape, dendrons are useful to create shape-controlled nanostructures and nanoobjects. 4 An important issue in dendrimer chemistry is the incorporation of chiral units into cascade-branched structures. This may be realized either by suitable end group functionalization5 or by the use of chiral building blocks. 6, 7 However, hitherto only a few examples of chiral dendrons have been reported. 8, 9In contrast to the tediously constructed dendrimers, hyperbranched polymers are cascade-branched structures prepared by a one-pot synthesis of ABm-or latent ABm-type monomers. 10 Thus, their architecture is less perfectly branched; ie, linear, dendritic, and terminal units are incorporated randomly. In contrast to dendrimers, hyperbranched polymers do not possess a gradient of structural density. So far, hyperbranched polymers have been regarded as poorly defined because of their commonly broad polydispersities and the lack of control over the core incorporation. 10 Recently, we reported the preparation of highly defined hyperbranched polyglycerols, based on the ring-opening multibranching polymerization of glycidol (ROMBP). 11 Due to the chain-growth nature of this process, these macromolecules possess the initiator employed as core unit and can be prepared in a molecular weight range between 1000 and 10 000, with narrow polydispersities Mw/Mn< 1.5 (mostly< 1.3). Molecular weights are controlled by the monomer/initiator ratio. In this Communication we report the first synthesis of chiral hyperbranched polymers and chiral hyperbranched dendron analogues 1, based on the polymerization of both commercially available enantiomers of glycidol (Scheme 1). Incorporation of precisely one functional group at the core was achieved via an initiator bearing a functional group, ie, a terminal double bond. Chiral polyglycerols in general may be suitable in the separation of enantiomers, in chiral catalysis, or for biochemical applications. The single double bond attached to the focal unit in the dendronlike structure is accessible for a variety of further functionalization methods by common olefin reactions,