Degree of chain branching-dependent assemblies and conducting behavior in ionic liquid crystalline Janus dendrimers
作者:Jin-Woo Choi、Byoung-Ki Cho
DOI:10.1039/c0sm01435d
日期:——
We prepared two Janus dendrimers 1 and 2 bearing a hydrophobic Percec-type minidendron (i.e., 3,4,5-tridodecyloxybenzyl group) and hydrophilic aliphatic ether dendrons with different degrees of branching via stepwise click reactions. The obtained Janus dendrimers have the same hydrophilic volume fraction (f = 0.34), but a different number of hydrophilic chains, i.e., tetrabranched and dibranched oligo(ethylene oxide) coils for 1 and 2, respectively. Upon doping with lithium salt, liquid crystalline (LC) ionic samples 1-Li+++ and 2-Li++ were obtained. As characterized by polarized optical microscopy (POM) and X-ray scattering techniques, 1-Li+++ showed an optically isotropic cubic LC phase, while 2-Li++ displayed a birefringent hexagonal columnar LC structure with a bilayered cross-section. Interestingly, the conductivity values of the cubic phase were considerably higher than those of the columnar phase, with which the cubic phase could be assigned as a bicontinuous cubic structure rather than a micellar one. On the basis of the experimental observations, the morphological contrast between two ionic Janus dendrimers is strongly attributed to the degree of chain branching, which is one of the major parameters governing the morphological features in the Janus dendrimer assemblies.
我们合成了两种Janus树枝状高分子1和2,分别具有疏水性的Percec型小树枝(即3,4,5-三十二烷氧基苯基基团)和带有不同分支程度的亲水性脂肪醚树枝,采用逐步的点击反应制备而成。获得的Janus树枝状高分子具有相同的亲水体积分数(f = 0.34),但亲水链的数量不同,即1为四分支,2为二分支的聚(氧化乙烯)卷曲。通过掺杂锂盐,获得了液晶(LC)离子样品1-Li+++和2-Li++。经过偏光显微镜(POM)和X射线散射技术的表征,1-Li+++展现出光学各向同性的立方液晶相,而2-Li++则显示出双折射的六角柱状液晶结构,具有双层交叉截面。有趣的是,立方相的电导率值明显高于柱状相,因此立方相可以被归类为双连续立方结构,而非胶束结构。根据实验观察,两种离子Janus树枝状高分子之间的形态对比主要归因于链的分支程度,这是影响Janus树枝状高分子组装中形态特征的主要参数之一。