Studies on Helicity Induction of Polymers and its Memory

具有可控螺旋感的螺旋聚合物的合成由于其有趣的结构和在材料科学中的潜在应用，近年来引起了聚合物化学领域的广泛关注。最近，我们发现在非旋光性聚苯基乙炔中，如聚（4-羧基苯基）乙炔（PCPA）在DMSO中与手性胺络合后，可以诱导以单手螺旋为主的大分子螺旋度，从而在聚合物主链上表现出诱导的圆二色性（ICD）。此外，发现非手性胺取代手性胺后，诱导的螺旋结构被记忆。本文通过红外光谱、紫外光谱和CD光谱研究了螺旋性诱导和螺旋手性记忆的机理。我们发现，当PCPA的羧基与手性胺形成离子对时，PCPA上的单手螺旋被协同诱导。另一方面，当手性胺被非手性胺取代后，自由吨的形成对于PCPA的大分子螺旋记忆是必不可少的，因为邻近羧酸离子之间的分子内静电斥力有助于减少PCPA的反异构化过程。在解决机理的基础上，我们发现过量的非手性胺与少量手性胺共存导致ICD的急剧增加，与过量手性胺诱导的完全ICD相当。诱导的单手螺旋型PCPA进一步被非手性胺成功记忆。类似的大分子螺旋诱导和对螺旋手性的记忆对于非旋光性多异氰化物是可能的，因此这一概念可能是普遍的，并且可以作为一种有希望的方法来构建具有所需垂链的单手螺旋阵列的新型功能螺旋聚合物。

The synthesis of helical polymers with controlled helix-sense has aroused considerable interest in polymer chemistry in recent years because of their interesting structures and their possible applications in materials science. Recently, we found that macromolecular helicity with a predominantly one-handed helix can be induced in optically inactive poly(phenylacetylenes), for instance, poly((4-carboxyphenyl)acetylene) (PCPA) upon complexation with chiral amines in DMSO, thus exhibiting an induced circular dichroism (ICD) in the polymer main chain. Moreover, the induced helical structure was found to be memorized after replacement of the chiral amines by achiral amines. In this study, we investigated the mechanism of the helicity induction and the memory of helical chirality by means of IR, UV, and CD spectroscopies.We found that a one-handed helix is cooperatively induced on PCPA upon ion pair formation of the carboxy groups of PCPA with chiral amines. On the other hand, the free tons formation is essential for the macromolecular helicity memory of PCPA after the replacement of the chiral amines with achiral amines, since the intramolecular electrostatic repulsion between the neighboring carboxylate ions contributes to reduce the atropisomerization process of PCPA. On the basis of the solved mechanism, we found that the coexistence of the excess bulky, achiral amine with a small amount of chiral amine caused a dramatic increase in the ICD being comparable to the full ICD induced by excess chiral amine. The induced one-handed helical PCPA was further successfully memorized by achiral amines.A similar macromolecular helicity induction and the memory of the helical chirality was possible for an optically inactive polyisocyanide, so that this concept may be general and can be used as a promising method to construct novel, functional helical polymers with the desired pendant in a one-handed helical array.