Network phases in ABC triblock copolymers
Network phases in ABC triblock copolymers
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DOI：
10.1021/ma0493426
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发表时间：
2004-09-21
期刊：
影响因子：
5.5
通讯作者：
Bates, FS
中科院分区：
文献类型：
--
作者：
Epps, TH;Cochran, EW;Bates, FS
许多天然产物和工程产物都受到网络结构的影响。胶原蛋白网络为活组织提供支架，而物理交联的多肽的溶胀阵列构成明胶，熟悉的甜点和电泳介质。尽管相关的网格尺寸相差几个数量级，但这些示例具有共同的功能：赋予机械刚性的三维连接性。嵌入额外的互连组件可以产生更广泛的功能，例如离子或导电性、光学带隙以及定制的传热和传质。1-3在介观长度尺度（大约在1纳米和1微米之间），界面曲率和堆积几何形状通常反映了具有规定结构和定向相互作用的分子的自组装。4在适当的条件下，水合皂、脂质和表面活性剂形成柔软的、可渗透的、双连续的固体，5-7一些能够模板化硬的中孔陶瓷网络。嵌段共聚物在操纵工程材料在过多的纳米级配置中的精确放置方面提供了更大的灵活性。10，11然而，除了两种块类型（AB，阿坝，ABAB等）的线性排列之外，目前还没有可靠的方法从理论上预测嵌段共聚物的形态。本通讯总结了一个全面的调查，一组同源的线性聚（异戊二烯-b-苯乙烯-b-环氧乙烷）（ISO）三嵌段共聚物。在过去的4年里，我们已经合成并表征了80多种ISO三嵌段共聚物，涵盖了广泛的组成。在这里，我们集中在总共43个模型化合物（Mw/Mn< 1.08），分子量为15< Mw< 25 kg/mol，组成以0.20 e fI e 0.58、0.25 e fS e 0.58和0 e fO e 0.37为界，其中fi是嵌段i的体积分数，由实验测定的重量分数和公开的在140 ℃下的均聚物密度计算：FI）0.830，FS）0.969，和FO）1.064 g/mol。12图1所示的三角形相图中确定了相关的相位。这里描述的实验在高于100 ℃进行，这超过了熔融（Tm，O= 65 ℃）和玻璃化转变（Tg，S= 90 ℃）温度。大多数嵌段共聚物表现出高于100 ℃，通常低于250 ℃的有序-无序转变温度（TODT）。有序相已被确定使用四种技术的补充：小角度X射线散射（SAXS）在先进的光子源（APS，阿贡国家实验室）或明尼苏达大学，透射电子显微镜（TEM），光去偏振（双折射），和动态力学光谱（DMS）。先前对位于由fI）fS定义的等值线上的ISO聚合物子集的实验表明，三重连续网络相（暂时与Fddd空间群对称性相关）将两域（I和S）和三域（I，S和O）层状状态分开。图13从位于标记为O 70的组成窗口（见图1）中的样品获得的代表性SAXS粉末图案是：
Many naturally occurring and engineered products are influenced by network structures. Collagen networks provide a scaffold for living tissue, while swollen arrays of physically cross-linked polypeptides constitute gelatin, the familiar dessert and electrophoresis medium. Although the associated mesh sizes differ by several orders of magnitude, these examples share a common feature: three-dimensional connectivity that imparts mechanical rigidity. Intercalating additional interconnected components can yield broader functions, eg, ionic or electrical conductivity, optical band gaps, and tailored heat and mass transfer. 1-3 At mesoscopic length scales (between roughly one nanometer and one micron) interfacial curvature and packing geometry often reflect self-assembly of molecules endowed with prescribed architectures and directed interactions. 4 Under the appropriate conditions, hydrated soaps, lipids, and surfactants form soft, permeable, bicontinuous solids, 5-7 some capable of templating hard mesoporous ceramic networks. 8, 9 Block copolymers provide even greater flexibility in manipulating the precise placement of engineering materials in a plethora of nanoscale configurations. 10, 11 However, aside from linear permutations of two block types (AB, ABA, ABAB, etc.) there is currently no reliable way to anticipate block copolymer morphologies from theory. This communication summarizes a comprehensive investigation of a homologous set of linear poly (isoprene-b-styrene-b-ethylene oxide)(ISO) triblock copolymers. We have synthesized and characterized more than eighty ISO triblock copolymers over the past 4 years, covering a wide range of compositions. Here we focus on a total of 43 model compounds (Mw/Mn< 1.08) with molecular weights 15< Mw< 25 kg/mol and compositions bounded by 0.20 e fI e 0.58, 0.25 e fS e 0.58, and 0 e fO e 0.37, where fi is the volume fraction of block i, calculated from the experimentally determined weight fractions and published homopolymer densities at 140 C: FI) 0.830, FS) 0.969, and FO) 1.064 g/mol. 12 The associated phases are identified in the triangular phase portrait illustrated in Figure 1. The experiments described here were conducted above 100 C, which exceeds the melting (Tm, O= 65 C) and glass transition (Tg, S= 90 C) temperatures. Most of the block copolymers exhibited an order-disorder transition temperature (TODT) above 100 C, and generally below 250 C. Ordered phases have been identified using a complement of four techniques: small-angle X-ray scattering (SAXS) performed at the Advanced Photon Source (APS, Argonne National Laboratory) or the University of Minnesota, transmission electron microscopy (TEM), light depolarization (birefringence), and dynamic mechanical spectroscopy (DMS). Previous experiments with a subset of the ISO polymers, located on the isopleth defined by fI) fS, indicated that a triply continuous network phase (tentatively associated with Fddd space group symmetry) separated the two-domain (I and S) and three-domain (I, S, and O) lamellar states. 13 A representative SAXS powder pattern, obtained from a specimen located in the composition window labeled O70 (see Figure 1), is