Key Laboratory of Polymeric Materials and Application Technology of Hunan Province, College of Chemistry, Xiangtan University, Xiangtan 411105, Hunan Province, China.
J Am Chem Soc. 2010 Jun 16;132(23):8071-80. doi: 10.1021/ja101184u.
The liquid-crystalline (LC) phase structures and transitions of a combined main-chain/side-chain LC polymer (MCSCLCP) 1 obtained from radical polymerization of a 2-vinylterephthalate, poly(2,5-bis{[6-(4-butoxy-4'-oxybiphenyl) hexyl]oxycarbonyl}styrene), were studied using differential scanning calorimetry, one- and two-dimensional wide-angle X-ray diffraction (1D and 2D WAXD), and polarized light microscopy. We have found that 1 with sufficiently high molecular weight can self-assemble into a hierarchical structure with double orderings on the nanometer and subnanometer scales at low temperatures. The main chains of 1, which are rodlike as a result of the "jacketing" effect generated by the central rigid portion of the side chains laterally attached to every second carbon atom along the polyethylene backbone, form a 2D centered rectangular scaffold. The biphenyl-containing side chains fill the space between the main chains, forming a smectic E (SmE)-like structure with the side-chain axis perpendicular to that of the main chain. This biaxial orientation of 1 was confirmed by our 2D WAXD experiments through three orthogonal directions. The main-chain scaffold remains when the SmE-like packing is melted at elevated temperatures. Further heating leads to a normal smectic A (SmA) structure followed by the isotropic state. We found that when an external electric field was applied, the main-chain scaffold greatly inhibited the motion of the biphenyls. While the main chains gain a sufficiently high mobility in the SmA phase, macroscopic orientation of 1 can be achieved using a rather weak electric field, implying that the main and side chains with orthogonal directions can move cooperatively. Our work demonstrates that when two separate components, one offering the "jacketing" effect to the normally flexible backbone and the other with mesogens that form surrounding LC phases, are introduced simultaneously into the side chains, the polymer obtained can be described as an MCSCLCP with a fascinating hierarchically ordered structure.
一种通过自由基聚合得到的主链/侧链液晶聚合物（MCSCLCP）1 的液晶（LC）相结构和转变，使用差示扫描量热法、一维和二维广角 X 射线衍射（1D 和 2D WAXD）以及偏光显微镜进行了研究。我们发现，具有足够高分子量的 1 可以在低温下自组装成具有纳米和亚纳米尺度上双重有序的分级结构。由于侧链中每个第二个碳原子上的中心刚性部分横向连接的“套壳”效应，1 的主链呈棒状，形成二维中心矩形支架。含联苯的侧链填充在主链之间的空间中，形成侧链轴垂直于主链轴的类似向列相 E（SmE）结构。我们的 2D WAXD 实验通过三个正交方向证实了 1 的这种双轴取向。在升高的温度下，类似 SmE 的堆积物熔融时，主链支架仍然存在。进一步加热导致正常的向列 A（SmA）结构，然后是各向同性状态。我们发现，当施加外部电场时，主链支架极大地抑制了联苯的运动。虽然主链在 SmA 相中获得了足够高的流动性，但可以使用较弱的电场实现 1 的宏观取向，这意味着具有正交方向的主链和侧链可以协同运动。我们的工作表明，当同时将两个单独的组件引入侧链中，一个提供通常灵活的骨架的“套壳”效应，另一个具有形成周围 LC 相的介晶时，所得到的聚合物可以被描述为具有迷人的分级有序结构的 MCSCLCP。
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