Studies on Helicity Induction of Polymers and its Memory

近年来，具有可控螺旋方向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而引起了高分子化学的极大兴趣。最近，我们发现，具有主要是单手螺旋的大分子螺旋性可以在光学惰性的聚（苯乙炔），例如，聚（（4-羧基苯基）乙炔）（PCPA）与手性胺在DMSO中络合后诱导，从而在聚合物主链中表现出诱导的圆二色性（ICD）。此外，在用非手性胺取代手性胺后，发现诱导的螺旋结构被记忆。本研究通过红外光谱、紫外光谱和圆二色光谱研究了PCPA的螺旋性诱导和螺旋手性记忆的机理，发现PCPA的羧基与手性胺形成离子对后，PCPA的单手螺旋被协同诱导。另一方面，自由吨的形成是必不可少的大分子螺旋记忆的手性胺取代后，与非手性胺，因为分子内的静电排斥相邻的羧酸根离子之间有助于减少阻转异构过程的PCPA。在解决的机制的基础上，我们发现，过量的庞大的，非手性胺与少量的手性胺的共存引起的ICD的急剧增加是由过量的手性胺诱导的完全ICD相媲美。通过对非手性胺的记忆，发现非旋光多异氰酸酯也能对大分子的螺旋性产生类似的诱导和记忆作用，这一概念具有普遍性，可作为一种新的单手螺旋结构的功能化螺旋聚合物的制备方法。

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.