Combined Main-Chain/Side-Chain Liquid Crystalline Polymer with Main-Chain On the basis of 鈥淛acketing鈥?Effect and Side-Chain Containing Azobenzene Groups

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• 作者：He-Lou Xie ; Shao-Jie Wang ; Guan-Qun Zhong ; Yi-Xin Liu ; Hai-Liang Zhang ; Er-Qiang Chen
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：October 11, 2011
• 年：2011
• 卷：44
• 期：19
• 页码：7600-7609
• 全文大小：1093K
• 年卷期：v.44,no.19(October 11, 2011)
• ISSN：1520-5835

文摘

Combining the concept of 鈥渇lexible spacer鈥?which can bring liquid crystalline (LC) properties to the side-chains and the side-group 鈥渏acketing鈥?effect which can result in main-chain with rod-like conformation, we have synthesized a new combined main-chain/side-chain LC polymer based on radical polymerization, poly(2,5-bis{[6-(4-methoxy-4鈥?oxy-azobenzene)hexyl]oxycarbonyl}styrene) (denoted as P₁) with two azobenzene groups per repeating unit. The chemical structures of P₁ and the corresponding monomer were characterized using various techniques with satisfactory analysis data. The phase structures and transitions of P₁ were investigated using differential scanning calorimetry, polarized optical microscope, and one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction. We identify that P₁ can form a hierarchically ordered structure with double orderings on both the nanometer and subnanometer length scales. Most likely, the thick main-chains of P₁ obtained by 鈥渏acketing鈥?the central rigid portion of terephthalate side-chain to the polyethylene backbone construct a 2D centered rectangular scaffold, which is stable until the sample becomes completely isotropic. The packing of side-chains inside the main-chain scaffold undergoes the transitions of smectic B- (SmB-) like 鈫?smecitc A (SmA)-like 鈫?isotropic. The confinement arising from the scaffold induces the SmB-like packing and enhances the stability of SmA-like structure. The hierarchically ordered structure of P₁ renders a biaxial orientation with the side-chains perpendicular to the main-chains. We compared P₁ with an end-on side-chain LC polymer of poly(4-{[6-(4-methoxy-4鈥?oxy-azobenzene)hexyl]oxycarbonyl}styrene) (denoted as P₂). P₂ bearing one mesogenic group per repeating unit forms a monolayer SmA phase, with the transition temperature much lower than that of P₁. Upon UV irradiation, in contrast to that P₂ will become isotropic, P₁ can still exhibit LC behavior after the azobenzene groups adopt cis conformation.