Precise polyethylene derivatives bearing mesogenic side-chains: delicate self-assembly depending on graft density

• Published in: Polymer chemistry Vol. 11; no. 8; pp. 1454 - 1461
• Main Authors: Chang, Wen-Ying, Shi, Dong, Jiang, Xu-Qiang, Jiang, Jia-Di, Zhao, Yang, Ren, Xiang-Kui, Yang, Shuang, Chen, Er-Qiang
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 28.02.2020
• Subjects: Aliphatic compounds; Backbone; Chains (polymeric); Columnar structure; Coupling (molecular); Crystal structure; Derivatives; Electron density; Grafting; Liquid crystal polymers; Liquid crystals; Molecular conformation; NMR; Nuclear magnetic resonance; Phase transitions; Polyethylene; Polyethylenes; Polymer chemistry; Self-assembly
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/c9py01856e

To achieve desirable properties of side-chain polymers, elaborately manipulating the interplay between the polymer backbone and side-chains is vital, which can be done by adjusting the graft density of side-chains. Here, we report a series of polyethylene derivatives with the aromatic biphenyl side-chains precisely grafted on every 2 nd , 7 th and 15 th carbon ( P n s, n = 2, 7, and 15) along the aliphatic backbone, the graft densities of which are nearly 4, 1, and 0.5 side-chains per nanometer, respectively. The self-assembly structures and phase transitions of P n s were investigated using various techniques. We demonstrate that precisely adjusting the distance between two adjacent side-chains, i.e. , the side-chain spacing, can drastically alter the local coupling of the backbone and rod-like mesogenic side-chains, leading to different backbone conformations and anisotropic interactions. Compared to P2 that is an ordinary side-chain liquid crystalline polymer (SCLCP) forming a crystal E phase, P7 and P15 exhibit a three-dimensionally (3D) ordered structure K X and a two-dimensional (2D) rectangular columnar phase Col R , respectively, which are unprecedented in SCLCPs. Moreover, the phase transition pathway can also be modified remarkably when the graft density is varied. Precise polyethylene derivatives bearing mesogenic side-chains demonstrate a sophisticated side-chain spacing effect on the local coupling and spatial arrangement of the backbone and side-chains.