Controlling the self-assembly of block copolymers with variable chain shape and stiffness is important for driving the self-assembly of functional materials containing nonideal chains as well as for developing materials with new mesostructures and unique thermodynamic interactions. The polymer helix is a particularly important functional motif. In the helical chain, the traditional scaling relationships between local chain stiffness and space-filling properties are not applicable; this in turn impacts the scaling relationships critical for governing self-assembly. Polypeptoids, a class of sequence-defined peptidomimetic polymers with controlled helical secondary structure, were used to systematically investigate the impact of helical chain shape on block copolymer self-assembly in a series of poly(n-butyl acrylate)-b-polypeptoid block copolymers. Small-angle X-ray scattering (SAXS) of the bulk materials shows that block copolymers form hexagonally packed cylinder domains. By leveraging sequence control, the polypeptoid block was controlled to form a helix only at the part either adjacent to or distant from the block junction. Differences in domain size from SAXS reveal that chain stretching of the helix near the block junction is disfavored, while helical segments at the center of cylindrical domains contribute to unfavorable packing interactions, increasing domain size. Finally, temperature-dependent SAXS shows that helix-containing diblock copolymers disorder at lower temperatures than the equivalent unstructured diblock copolymers; we attribute this to the smaller effective N of the helical structure resulting in a larger entropic gain upon disordering. These results emphasize how current descriptions of rod/coil interactions and conformational asymmetry for coil polymers do not adequately address the behavior of chain secondary structures, where the scalings of space-filling and stiff–elastic properties relative to chain stiffness deviate from those of typical coil, semiflexible, and rodlike polymers.

中文翻译：

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序列确定的聚合物中螺旋链形状对类肽嵌段共聚物自组装的影响

控制具有可变链形状和刚度的嵌段共聚物的自组装对于驱动包含非理想链的功能材料的自组装以及开发具有新的介孔结构和独特的热力学相互作用的材料非常重要。聚合物螺旋是特别重要的功能性基序。在螺旋链中，局部链刚度和空间填充特性之间的传统缩放关系不适用；这反过来影响了对于控制自组装至关重要的缩放关系。多肽类是一类具有受控的螺旋二级结构的序列定义的拟肽聚合物，用于系统研究一系列聚（n-丙烯酸丁酯）-b-类肽嵌段共聚物。散装材料的小角X射线散射（SAXS）表明，嵌段共聚物形成了六方堆积的圆柱域。通过利用序列控制，控制多肽肽嵌段以仅在与嵌段连接相邻或远离的部分形成螺旋。与SAXS的域大小不同表明，嵌段连接附近的螺旋链的拉伸受到不利影响，而圆柱域中心的螺旋段则不利于堆积相互作用，从而增加了域的大小。最后，与温度有关的SAXS表明，在较低的温度下，含螺旋的二嵌段共聚物比同等的非结构化二嵌段共聚物无序。我们将其归因于较小的有效N螺旋结构的“α”导致无序时更大的熵增益。这些结果强调了当前关于线圈聚合物的杆/线圈相互作用和构象不对称的描述如何不能充分解决链二级结构的行为，在该结构中，相对于链刚度的空间填充和刚弹特性的缩放比例与典型线圈的比例不同，半柔性和棒状聚合物。