含侧链盘状苯并菲和棒状偶氮苯的二嵌段液晶共聚物的可控合成及其光物理性质

Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side-Chain Discotic Triphylene and Calamitic Azobenzene Mesogens

分别通过可逆加成-断裂链转移(RAFT)聚合和原子转移自由基聚合(ATRP)结合叠氮-端炔基大分子点击反应,制备了一系列不同聚合度和不同嵌段比例的基于侧链苯并菲TP盘状液晶基元和偶氮苯Azo棒状液晶基元的盘棒杂化二嵌段共聚物。采用核磁共振氢谱(1H NMR)、凝胶渗透色谱(GPC)、差示扫描量热分析(DSC)和正交偏光分析(POM)对盘棒杂化二嵌段共聚物的组成结构、相对分子质量和液晶相行为进行了表征。偶氮苯嵌段较短的共聚物P(TP_(6))_(40)-b-P(Azo)_(10),主要表现出占优势嵌段TP盘状液晶聚合物的热转变温度与相行为。而偶氮苯嵌段较长的共聚物P(TP_(6))_(10)-b-P(Azo)_(40)和P(TP_(6))_(40)-b-P(Azo)_(40)则更多体现出类似Azo棒状侧链液晶聚合物的相行为和光响应特性。小角/广角X射线散射(SAXS/WAXS)分析证实了Azo嵌段较长的嵌段共聚物薄膜尤其经退火处理后呈现层状结构,倾向于平行基底取向排布的苯并菲诱导偶氮苯平躺沿着平行基底方向排列而显著减少了光吸收,经紫外及可见光的辐照后光吸收显著增大,其中盘状嵌段较长的P(TP_(6))_(40)-b-P(Azo)_(40)对比响应增幅尤其明显。这种盘棒杂化二嵌段共聚物薄膜所表现出的特殊光物理性质及其快速光响应-回复特性,加深了对其相互作用的理解,可望为设计合成新的光响应材料提供参考依据。

A series of disk-rod hybrid diblock copolymers based on side-chain discotic triphenylene(TP)and calamitic azobenzene(Azo)mesogens with different length and ratio of the two block segments were well prepared via copper(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition(CuAAC)click reaction.The reactive precursor blocks were synthesized through atom transfer radical polymerization(ATRP)or reversible addition-fragmentation chain transfer(RAFT)polymerization of Azo methacrylate and TP acrylate monomers using specially designed chain transfer agent and initiator with different functional groups.The structure,molecular mass and liquid crystalline phase behaviors of the thus obtained disk-rod diblock copolymers were characterized by ^(1)H nuclear magnetic resonance(NMR)spectroscopy,gel permeation chromatography(GPC),differential scanning calorimetry(DSC)and polarization optical microscopy(POM).The hybrid diblock copolymer of P(TP_(6))_(40)-b-P(Azo)_(10);with a shorter azobenzene block segment,mainly exhibits the thermal transition temperature and phase behavior of the dominant TP-based discotic liquid crystalline polymer(LCP).While the copolymers of P(TP_(6))_(10)-b-P(Azo)_(40);and P(TP_(6))_(40)-b-P(Azo)_(40) with a longer azobenzene block segment,reflect more of the phase behavior and photoresponse properties of the Azo-based side-chain LCP.Small-angle/wide-angle X-ray scattering(SAXS/WAXS)analysis confirms that the diblock copolymer films with a longer Azo-based segment are in a layered structure especially after annealing,the Azo mesogens are arranged in a flat lying orientation in parallel with the quartz substrate induced by the planar oriented TP mesogens,which significantly reduce the light absorbance of the UV-Vis spectra,then the light absorbance increases obviously after irradiation with 365 nm ultraviolet and then visible light,where P(TP_(6))_(40)-b-P(Azo)_(40) with the longer TP-based block shows a particularly prominent increment.The study on the unique photophysical properties and specific photoresponse behaviors of such disk-rod hybrid diblock copolymer films can help to deepen the understanding of their interactions and are expected to provide guidance for the design and synthesis of novel photoresponsive materials.