Well-Defined Star-Shaped Poly(p-benzamide) via Chain-Growth Condensation Polymerization: Use of Tetra-Functional Porphyrin Initiator to Optimize Star Polymer Formation
Well-Defined Star-Shaped Poly(p-benzamide) via Chain-Growth Condensation Polymerization: Use of Tetra-Functional Porphyrin Initiator to Optimize Star Polymer Formation
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通过链增长缩合聚合形成明确的星形聚对苯甲酰胺：使用四官能卟啉引发剂优化星形聚合物的形成
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发表时间：
2009
期刊：
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通讯作者：
T. Yokozawa
中科院分区：
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作者：
Kazuo Yoshino;A. Yokoyama;T. Yokozawa
大多数星形聚合物的分子量可控，多分散性低，是通过活聚合合成的，其中只有引发和传播反应，没有链转移反应。因此，所得到的星形聚合物一般不受线性聚合物的污染。近年来，我们发展了链式缩聚，这是一种分子量可控、分子量分布窄的缩聚聚合物。然而，采用该方法合成星形聚（对苯酰胺）s时，使用多功能引发剂，不仅可以通过链式聚合得到所需的星形聚（对苯酰胺），而且当引发剂用量减少时，还可以通过单体自缩聚得到线状聚（苯酰胺）。在相同条件下，与单功能引发剂的链生长缩聚反应相比，线性聚合物的这种污染更容易发生。此外，还需要用高效液相色谱（HPLC）对产物进行分离，以确定哪些产物是星形聚合物，哪些是线状聚合物。然而，利用含卟啉的引发剂，其最大吸收峰在430 nm左右，与聚对苯酰胺的吸收峰有很大的不同，利用变波长紫外探测器的GPC，我们可以很容易地区分出含卟啉引发单元的星形聚合物和不含卟啉引发单元的线型聚合物，从而优化聚合条件，选择性合成星形芳香族聚酰胺。此外，与具有柔性线圈聚合物臂的星形聚合物相比，具有刚性臂的卟啉核星形聚合物的合成报道相当少。例如，在含有四个碘芴基团的卟啉存在下，由溴芴硼酯铃木偶联缩聚合成卟啉核星型聚芴。在这种聚合中，聚臂长度不受控制，分子量分布较宽。因此，具有明确刚性臂或半刚性臂的卟啉核星形聚合物的合成和性质仍有待充分确定。本文研究了以卟啉为核心的四功能引发剂3在不同条件下的4-（辛胺）苯甲酸酯1的链生长缩聚反应，并优化了选择性合成星形聚（对苯酰胺）s的条件，抑制了线性自缩聚聚酰胺的形成（方案1）。
Most star polymers with controlled molecular weight and low polydispersity are synthesized by living polymerization, in which only initiation and propagation reactions, but not chain transfer reaction, take place. Accordingly, the obtained star polymers are generally not contaminated with linear polymers. Recently, we have developed chain-growth condensation polymerization, a kind of living polymerization yielding condensation polymers with controlled molecular weight and narrow molecular weight distribution. However, synthesis of star-shaped poly(p-benzamide)s through this method, using multifunctional initiators, afforded not only the desired star-shaped poly(p-benzamide) via chain-growth polymerization, but also a linear poly(pbenzamide) via self-polycondensation of the monomer when the amount of the initiator was decreased. This contamination with linear polymer was more liable to occur as compared to the case of chain-growth condensation polymerization with a monofunctional initiator under the same conditions. In addition, separation of the products by means of high-performance liquid chromatography (HPLC) was necessary to confirm which product was the star polymer and which the linear polymer. However, by using an initiator containing porphyrin, the absorption maximum of which is around 430 nm and quite different from that of poly(p-benzamide), we could easily differentiate the star polymer bearing the porphyrin initiator unit from the linear polymer without this initiator unit by means of GPC with a variable-wavelength UV detector, and thus we could optimize the polymerization conditions for selective synthesis of star aromatic polyamides. Furthermore, there are rather few reports on the synthesis of porphyrin-cored star polymers with rigid arms, as compared with star polymers with flexible-coil polymer arms. For example, porphyrin-cored star polyfluorene was synthesized by Suzuki coupling polycondensation of bromofluorene boronic ester in the presence of a porphyrin having four iodofluorene moieties. In this polymerization, the length of the arms was not controlled and the molecular weight distribution was broad. Therefore, not only the synthesis, but also the properties of porphyrin-cored star polymers with well-defined rigid or semirigid arms remain to be fully established. In this article, we investigated the chain-growth condensation polymerization of 4-(octylamino)benzoic acid esters 1 with porphyrin-cored tetra-functional initiator 3 under various conditions and optimized the conditions for selective synthesis of star-shaped poly(p-benzamide)s with suppression of the formation of linear selfcondensed polyamides (Scheme 1).