基于柔性液晶基元调控侧链液晶高分子的构象和相结构

In this project, we intend to realize the contronl of molecular shape and hence phase structure of side-chain liquid crystalline polymers (SCLCPs) via use of molecular aspects. We will synthesize three series of SCLCPs, with the flexible rod-like and biforked mesogenic side-chain directly attached to the linear polyethylene backbone without flexible spacer. The flexible mesogen is based on the "phenyl-methyleneoxy-phenyl" moiety and terminated with alkyl tail of varied length. The flexible methyleneoxy unit has two most stable conformational isomers, anti and gauche, which are in dynamic equilibrium. The anti conformer has an extended conformation and display liquid crystallinity. The gauche conformer is similar to a "kinked" unit and, therefore, is expected to maximize "jacketing effect" of side-chain by bringing the side-chain much closer to the backbone. We intend to use the conformation isomerization of flexible mesogen to trigger lamellar-to-columnar phase transition . The influences of the flexibility of mesogen, the length of the alkyl tail, and the position of side-chain on the molecular shape and phase structure of the new SCLCPs will be studied by means of a combination of X-ray diffraction (XRD) , relative electron density reconstruction, molecular dynamic stimulation, temperature-depedent IR and NMR, and other methods. Ultimately, we aim to combine chemical structure with detailed structural characterization in an effort to expand fundamental understanding of the interaction between the main-chain and the side-chain and develop shape-persistent SCLCPs with flexible main-chain.

本项目拟通过合理的分子设计实现对侧链液晶高分子（SCLCP）的分子形状和相结构调控。在聚乙烯主链上侧接柔性液晶基元，通过改变液晶基元的刚柔性和形状、侧链的长度和位置，拟合成三个系列无间隔基的SCLCP。柔性液晶基元有两种最稳定的构象，反式和旁式，二者处于热力学动态的平衡。在主链与侧链强烈偶合的SCLCP中，反式构象异构体能赋予侧链液晶性；旁式构象异构体能最大化侧链的甲壳效应。本研究拟利用柔性液晶基元的构象反转在同一聚合物中实现层状相?柱状相调控。通过对聚合物X射线衍射分析、电子密度重构、分子动力学模拟，以及变温红外和核磁分析，我们拟总结化学结构与凝聚态结构之间的关系，探索合成含柔性主链和柔性侧链、具有持久分子形状的SCLCP新思路。

构象熵驱动聚合物链通常采取无规线团构象。因而，设计、合成持久形状的高分子并实现其分子尺寸、分子形状、分子排列、自组装结构的控制是高分子科学和高分子工程的一个中心问题。该项目主要研究侧链形状、尺寸、刚柔性以及主链刚柔性对液晶高分子（LCP）分子形状、分子尺寸、分子排列、相结构的影响。本项目合成了几类新的持久分子形状的LCP，并实现其分子尺寸从～1 nm到～6 nm、分子形状从片状到柱状、相结构从层状到柱状、超分子柱从“单链柱”到“多链柱”的调控。