侧基含羟基的主链偶氮苯液晶共聚酯的合成及其光响应行为

以4,4’-双(6-羟基己氧基)联苯(BHHBP)、4,4’-双(6-羟基己氧基)偶氮苯(BHHAB)为液晶基元,利用苹果酸二乙酯(DM)和苯基丁二酸(PSA)采用无规共聚,合成了侧基含羟基的偶氮苯液晶共聚酯(Az-LCP).先在液晶态下拉伸取向,然后用六亚甲基二异氰酸酯(HDI)交联制备单畴取向偶氮苯液晶交联网络.通过核磁共振氢谱(1H-NMR)、凝胶渗透色谱(GPC)测试,对合成的Az-LCP进行结构表征,通过示差扫描量热分析(DSC)、X射线衍射(XRD)、偏光光学显微镜(POM)等对其液晶相变行为进行表征,研究了偶氮苯含量、交联密度、薄膜厚度对其光致弯曲行为的影响.结果表明,偶氮苯含量10%,交联12 h的Az-LCP1具有最佳的光致弯曲回复行为.

Synthesis of Main-chain Azobenzene Liquid Crystalline Copolyester with Cide Hydroxyl Group and Its Photoresponsive Behavior

A series of main-chain azobenzene liquid crystalline copolyesters containing side hydroxyl group(Az-LCP)were synthesized with 4,4’-bis(6-hydroxyhexyloxy)biphenyl(BHHBP),4,4’-bis(6-hydroxyhexyloxy)azobenzene(BHHAB),diethyl malate(DM)and phenyl succinic acid(PSA)by random copolymerization.Chemical structure of the Az-LCPs was characterized by proton nuclear magnetic resonance(1 H-NMR)and gel permeation chromatography(GPC).And the phase transition behavior of the Az-LCPs was characterized by differential scanning calorimeter(DSC),and X-ray diffraction(XRD).Az-LCPs showed a nematic phase with a glass transition temperature(T_g)around room temperature.With increasing BHHAB monomer,the T_g and nematic-isotropic transition temperature of Az-LCPs decreased from 25.6℃and 96.4℃to 19℃and 88.2℃,respectively,showing a trans-cis photoisomerization effect of Az-LCPs.Then monodomain azobenzene liquid crystalline networks(Az-LCNs)were prepared by uniaxial stretching at nematic phase first,postcrosslinking in the hexamethylene diisocyanate solution for 12 h.Moreover,the orientation degree decreased with increasing BHHAB monomer into Az-LCP due to the decreasing T_g andπ-πstacking interaction.While being crosslinked with HDI,the T_g of Az-LCNs increased up to 40℃,meanwhile,the nematic-isotropic phase transition became broad and almost disappeared as the BHHAB monomer increased.All the Az-LCNs showed a UV-light induced bending and vis-light induced unbending behavior at room temperature except Az-LCN4 which contains 50%BHHAB monomer.Crosslinking duration of Az-LCNs also exhibited an influence on the photoresponsive bending/unbending behavior.With increasing crosslinking duration,the bending angle increased first and then decreased.In addition,the maximum bending angle and photoresponsive speed of Az-LCNs decreased with increasing thickness of the Az-LCNs films.Az-LCP1 with 10%azobenzene content and cross-linking for 12 h exhibits excellent photoresponsive behavior with a high bending angle of 88°and the fastest photoresponsive speed.