Impact of Helical Chain Shape in Sequence-Defined Polymers on Polypeptoid Block Copolymer Self-Assembly
Impact of Helical Chain Shape in Sequence-Defined Polymers on Polypeptoid Block Copolymer Self-Assembly
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DOI：
10.1021/acs.macromol.8b00055
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发表时间：
2018-03-13
期刊：
影响因子：
5.5
通讯作者：
Segalman, Rachel A.
中科院分区：
文献类型：
--
作者：
Davidson, Emily C.;Rosales, Adrianne M.;Segalman, Rachel A.
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含有非理想链的功能材料的自组装以及开发具有新的介观结构和独特的热力学相互作用的材料是重要的。聚合物螺旋是一个特别重要的功能基序。在螺旋链中，传统的局部链刚度和空间填充特性之间的比例关系是不适用的;这反过来又影响了控制自组装的关键比例关系。以一类具有可控螺旋二级结构的序列确定的拟肽聚合物--类多肽为研究对象，系统研究了一系列聚（丙烯酸正丁酯）-b-类多肽嵌段共聚物中螺旋链形状对嵌段共聚物自组装的影响.小角X-射线散射（SAXS）的散装材料表明，嵌段共聚物形成六边形填充的圆柱域。通过利用序列控制，控制类多肽块仅在邻近或远离块连接的部分形成螺旋。从SAXS域大小的差异表明，链拉伸的螺旋附近的块结是不利的，而在圆柱形域的中心的螺旋段有助于不利的包装相互作用，增加域的大小。最后，温度依赖性SAXS表明，含螺旋的二嵌段共聚物在较低的温度下比同等的非结构化的二嵌段共聚物的无序，我们将此归因于较小的有效N的螺旋结构，导致在一个较大的熵增益后无序。这些结果强调了如何目前的描述杆/线圈的相互作用和构象不对称的线圈聚合物没有充分解决链二级结构的行为，其中的缩放的空间填充和刚性弹性性能相对于链刚度偏离那些典型的线圈，半柔性，棒状聚合物。
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.