Well-Ordered Lamellar Microphase- Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle . Macromolecules
Well-Ordered Lamellar Microphase- Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle . Macromolecules
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含有主链液晶聚酯作为中间的 ABA 三嵌段共聚物的有序层状微相分离形态。
DOI：
10.1021/ma200409f
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发表时间：
2011
期刊：
影响因子：
5.5
通讯作者：
& Watanabe J.
中科院分区：
文献类型：
--
作者：
Ishige R.;Ishii T.;Tokita M.;Koga M.;Kang S.;& Watanabe J.
由液晶和各向同性嵌段组成的液晶嵌段共聚物由于以下两个方面而令人感兴趣。首先，由外场诱导的LC取向可以诱导微畴的宏观取向。微区遵循介晶取向以使指向矢畸变最小化。通过施加磁场，实现了液晶嵌段共聚物的大面积无定形圆柱体排列。1.3液晶相对于衬底的锚定诱导了薄膜中层状或非晶圆柱体的取向。4在剪切流动下，近晶液晶使层法线平行于速度梯度方向，因此浸入近晶液晶基质中的微柱虽然不能避免变形而倾斜，但必须在其取向上妥协，以便位于速度梯度方向。第二，LC可以影响微区形态。在液晶聚合物链段从各向同性相向非晶相转变时，非晶链段的形状由球形变为圆柱形，从而避免了液晶指向矢畸变。6近晶液晶嵌段共聚物在异常低的液晶组成下形成层状形态。7在某些近晶液晶嵌段共聚物中，在液晶温度范围内，随着温度的降低，片层间距增加，这对应于液晶链段构型从无规卷曲到在片层法线方向上更多延伸的变化。在这些共聚物中，LC链段是侧链型的，其中介晶部分通过柔性间隔基连接到聚合物主链。还制备了具有主链型LC链段的LC嵌段共聚物，其中介晶部分通过亚烷基间隔基连接以嵌入链骨架中;然而，它们面临着聚合产生均聚物和非预期嵌段排列以及嵌段共聚物的显著问题。11.13形态尚未报道，尽管它们的热转变很好地归因于每个链段的热转变，并表明LC和无定形链段彼此强烈分离。在这项研究中，我们报告的阿坝三嵌段共聚物组成的聚（甲基丙烯酸甲酯）（PMMA）作为无定形端嵌段（A）和主链液晶聚合物BB-5（3-Me）作为液晶中心嵌段（B）。这两种类型的节段彼此分离形成薄片，其显示出清晰的小角X射线散射（SAXS）轮廓。结合广角X射线衍射图和SAXS曲线的分析表明，轮廓长度为52 nm的BB-5（3-Me）片段形成了平行于厚度为11.6 nm的薄片的近晶层。该嵌段共聚物是通过甲基丙烯酸甲酯与Br封端的BB-5（3-Me）作为大分子引发剂的原子转移自由基聚合（ATRP）制备的（详细描述在支持信息中）。通过1H NMR谱估计BB-5（3-Me）链段（x）和两个PMMA链段之和（2 y）的聚合度（DP）分别为32和73。因此，BB-5（3-Me）和PMMA链段的数均分子量Mn分别计算为10 500和7300。通过凝胶渗透色谱法估计BB-5（3-Me）链段和嵌段共聚物的多分散性（Mw/Mn）分别为1.7和1.5。PMMA和BB-5（3-Me）片段的体积分数估计为1.5%。
Liquid crystal (LC) block copolymers composed of LC and isotropic blocks are interesting because of the following two aspects. First, the LC orientation induced by an external field can induce macroscopic orientation of the microdomains. The microdomains are following the mesogens orientation to minimize the director distortion. Large area amorphous cylinder alignments in LC block copolymers have been accomplished by application of a magnetic field. 1À3 The anchoring of the LC relative to the substrate induced orientations of lamellae or amorphous cylinders in the ultrathin films. 4 Under shear flow, a smectic LC aligns the layer normal parallel to the velocity gradient direction, so the microcylinders immersing in the smectic LC matrix have to compromise on their orientation so as to lie in the velocity gradient direction though they cannot avoid being tilted by the deformation. 5 Second, the LC can affect the microdomain morphology. On the transition from isotropic to nematic phases in the LC polymer segments, the amorphous segments changed their shape from sphere into cylinder so as to avoid LC director distortion. 6 Smectic LC block copolymers formed lamellar morphology at unusually low LC compositions. 7 In some smectic LC block copolymers, the lamellar spacing increased with decreasing temperature in the LC temperature region corresponding to the change of LC segment configuration from random coil to more extended in the lamellar normal direction. 8À10 In these copolymers, the LC segments are sidechain type in which the mesogenic moieties are connected to the polymer backbone by flexible spacers. LC block copolymers having main-chain type LC segments in which the mesogenic moieties are connected by alkylene spacers to be embedded in the chain backbone were also prepared; however, they were confronted with significant problems that the polymerization yielded the homopolymers and unintended block arrangements as well as the block copolymers. 11À13 The morphology has not been reported although their thermal transitions were well attributed to that of each segment and suggested that the LC and amorphous segments segregated strongly from each other. In this study, we report on an ABA triblock copolymer consisting of poly (methyl methacrylate)(PMMA) as amorphous end blocks (A) and main-chain LC polymer of BB-5 (3-Me) as the LC central block (B). These two types of segment were segregated each other to form lamellae which showed a clear small-angle X-ray scattering (SAXS) profile. Combining of the wide-angle X-ray diffraction pattern and an analysis of the SAXS profile demonstrates that the BB-5 (3-Me) segment with 52 nm in contour length formed smectic layers lying parallel to the lamella having a thickness of 11.6 nm. It clearly shows that the LC polymer chains in the smectic phase are folded at every seven repeat units.The block copolymer was prepared by atom transfer radical polymerization (ATRP) of methyl methacrylate with the Brterminated BB-5 (3-Me) as the macroinitiator (the details are described in Supporting Information). The degrees of polymerization (DP) of the BB-5 (3-Me) segment (x) and the sum of the two PMMA segments (2y) were estimated to be 32 and 73, respectively, by 1H NMR spectra. The number-average molecular weights Mn of the BB-5 (3-Me) and PMMA segments are thus calculated to be 10 500 and 7300, respectively. The polydispersities (Mw/Mn) of the BB-5 (3-Me) segment and the block copolymer were estimated to be 1.7 and 1.5, respectively, by gel permeation chromatography. The volume fractions of PMMA and BB-5 (3-Me) segments were estimated to be …