The effects of para-, meta- and ortho-monosubstituted azobenzene moiety in the side chain on phase behavior of mesogen-jacketed liquid crystalline polymers
smecitc C (SmC)-like structure. Furthermore, the glass transition temperature (Tg), isotropic temperature (Ti) and liquid crystalline range (ΔT, from Tg to Ti) of the polymers decrease in the order, para > meta > ortho. It is very interesting phenomenon that the associated enthalpy changes of these polymers are also the same order, para > meta > ortho, which is different from those of MCLCPs and SCLCPs
研究了在侧链具有单取代的偶氮苯部分的三种不同的介晶夹层液晶聚合物。这些是聚(2,5-双[对-(4'-甲氧基-4-氧基己氧基偶氮苯)苄基]氧羰基}苯乙烯)(表示为PPABCS),聚(2,5-双[间位-(4' -甲氧基-4-氧基己氧基氧基偶氮苯)苄基]氧羰基}苯乙烯)(表示为PMABCS)和聚(2,5-双[邻-(4'-甲氧基-4-氧基己氧基氧基偶氮苯)苄基]氧羰基}苯乙烯)(表示为作为POABCS)。单体的化学结构通过1 H NMR,13 C NMR光谱和元素分析确认。聚合物的结构表征通过1进行使用差示扫描量热法(DSC),偏振光显微镜(PLM)以及一维和二维(1D,2D)宽的1H NMR光谱学和凝胶渗透色谱法(GPC)以及聚合物的相结构和转变进行了研究角X射线衍射。还研究了不同位置的单取代偶氮苯部分对聚合物液晶行为的影响。结果表明,含有单取代的偶氮苯部分的介晶夹层液晶聚合物的相变行为强
Tailoring the liquid crystalline property via controlling the generation of dendronized polymers containing azobenzene mesogen
the first‐generationdendronizedpolymer exhibited liquidcrystalline behavior of the conventional side‐chain liquidcrystallinepolymer with azobenzenemesogen, that is, the polymer exhibited smectic phase structure at lower temperature and nematic phase structure at higher temperature. However, the second‐generationdendronizedpolymers exhibited more versatile intriguing liquidcrystalline structures
包含偶氮苯液晶元的第一代和第二代树枝状聚合物均已设计并通过自由基聚合成功合成。单体的化学结构通过元素分析,1 H NMR和13 C NMR确认。用1对聚合物进行分子表征1 H NMR和凝胶渗透色谱。使用差示扫描量热法,偏光显微镜和小角度X射线散射实验研究了相结构和跃迁行为。实验结果表明,第一代树枝状聚合物具有传统的带有偶氮苯介晶的侧链液晶聚合物的液晶行为,即该聚合物在较低温度下具有近晶相结构,在较高温度下具有向列相结构。然而,第二代树状化聚合物表现出更丰富的,有趣的液晶结构,即较低温度下的近晶相结构和较高温度下的柱状向列相结构,而且,该相结构仍保留在分解温度之前。
Synthesis and Phase Structures of Dendronized Polymers with Dendritic Azobenzene Side Groups Based on Mesogen-Jacketed Liquid Crystalline Polymers
The results show that the liquidcrystalline (LC) phase structures of the dendronized polymers containing dendritic azobenzene side groups depend strongly on the molecular weights (MWs) and the generation of dendritic azobenzene side groups. Compared the low MWs PG2 with the low MWs PG1, the degree of order in LC phase increased with increasing the generation of dendritic azobenzene side groups.
A series of azobenzene-tethered polyhedral oligomeric silsesquioxane (POSS) derivatives, i.e.monoazobenzene-substituted POSS (MonoAzo-POSS), bisazobenzene-substituted POSS (BisAzo-POSS) and triazobenzene-substituted POSS (TriAzo-POSS), were synthesized through the amidation acidylation of aminopropylisobutyl POSS and benzoic acid derivatives (AzoMs) with one, two and three azobenzene groups (AzoM1, AzoM2 and AzoM3). Their structures were characterized by FT-IR, 1H NMR, 13C NMR and mass spectra, and their thermal stability and photoresponsive behaviors in DMF solutions were evaluated with TGA, XRD and UV-vis spectra, respectively. The results indicated that the thermal stability and photoisomerization of azobenzenes could be effectively controlled by their molecular structure. In MonoAzo-POSS, the large steric hindrance of POSS destroys the molecular ordering and limits the molecular packing, contributing to its poor thermal stability. And the low molecular ordering of MonoAzo-POSS offers an azo group with large free space, and its trans–cisphotoisomerization rate increases accordingly. But, in BisAzo-POSS and TriAzo-POSS, the incorporation of POSS units does not impact on the regularity of azobenzenes obviously, and the hindrance effect of nanosize POSS on the molecular motion plays a primary role in increasing their high thermal stability. Their photoisomerization rates decrease due to the steric hindrance of POSS and the unfolding structure of the azo moieties in BisAzo-POSS and TriAzo-POSS.