Long range chirality transfer in free radical polymerization of vinylterphenyl monomers bearing chiral alkoxy groups
Long range chirality transfer in free radical polymerization of vinylterphenyl monomers bearing chiral alkoxy groups
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DOI：
10.1002/pola.26769
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发表时间：
2013-09
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影响因子：
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通讯作者：
Anhua Liu;Zhiyuan Zhao;Rong Wang;Jie Zhang;X. Wan
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文献类型：
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作者：
Anhua Liu;Zhiyuan Zhao;Rong Wang;Jie Zhang;X. Wan
合成了2-（4 ′-烷氧基苯基）-5-（4 ′-己氧基苯基）苯乙烯（S-Am（m= 0，1，2，3）/R-A0）和2-（4 ′-己氧基苯基）-5-（4 ′-烷氧基苯基）苯乙烯（S-Bm（m= 0，1，2，3）/R-B 0）两个系列的手性大体积乙烯基芳香化合物，并进行了自由基聚合。结合1H-NMR、13 C-NMR、旋光、圆二色谱、液晶诱导圆二色谱和计算机模拟研究了聚合过程中螺旋结构的产生和立体突变以及侧基立体中心向聚合物主链的手性转移。除S-B3外，所有聚合物在三联苯侧基的紫外-维斯吸收区均表现出旋光和Cotton效应，这与相应的模型化合物和单体有很大的不同，表明聚合物形成了手性二级结构，即侧基的歪斜堆积和主链的扭曲，具有明显的螺旋方向.当m从1增加到3时，旋光强度变小，旋光符号交替变化。然而，尽管S-A0和S-B 0中的立体中心比S-A1和S-B1中的立体中心更靠近乙烯基，但观察到较弱的手性诱导能力。此外，衍生自S-A0/R-A0和S-B 0/R-B 0的聚合物的旋光度符号相反，并随着在四氢呋喃中退火时间的增加而增加。这些结果与我们之前在类似的乙烯基三联苯化合物中的发现形成鲜明对比，其中-COO-而不是-O-将手性烷基尾部连接到三联苯基团，表现出侧基的小结构变化对聚合物手性光学性质和螺旋-有义-选择性聚合中手性转移的复杂性的显着影响。© 2013 Wiley Periodicals，Inc. J.波利姆科学，A部分：聚合物2013，51，3674-3687
Two series of chiral bulky vinyl aromatics, 2‐(4'‐alkoxyphenyl)‐5‐(4'‐hexyloxyphenyl)styrene (S‐Am(m= 0, 1, 2, 3)/R‐A0) and 2‐(4'‐hexyloxyphenyl)‐5‐(4'‐alkoxyphenyl)styrene (S‐Bm(m= 0, 1, 2, 3)/R‐B0), were synthesized and radically polymerized (wheremdenotes the carbon number between stereogenic center and ether oxygen atom). The generation and stereomutation of helical structures as well as chirality transfer from the stereogenic center of the side‐group to the polymer backbone during polymerization were investigated by a combination of1H‐ and13C‐NMR, polarimetry, circular dichroism spectroscopy, liquid crystal induced circular dichroism, and computer simulation. All the polymers, exceptS‐B3,display optical rotations and Cotton effects in the UV‐Vis absorption region of terphenyl pendant, which are quite different from the corresponding model compounds and monomers, suggesting the formation of chiral secondary structures, that is, skewed packing of side‐groups and twisting of polymer backbones with a dominant screw sense. The sign of optical rotation changes alternatively and the strength diminishes when m increases from 1 to 3. However, although the stereogenic centers inS‐A0andS‐B0are closer to the vinyl group than those inS‐A1andS‐B1,separately, a weaker chiral induction power is observed. Moreover, optical rotations of polymers derived fromS‐A0/R‐A0andS‐B0/R‐B0are opposite in sign and increase with annealing time in tetrahydrofuran. These results are in a sharp contrast with our previous findings in similar vinylterphenyl compounds, where ‐COO‐ rather than ‐O‐ links the chiral alkyl tail to the terphenyl group, manifesting a remarkable effect of small structural variation of side‐group on polymer chiroptical properties and complexity of chirality transfer in helix‐sense‐selective polymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3674–3687