螺旋链形状对薄片形成嵌段共聚物自组装的影响,Macromolecules

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螺旋链形状对薄片形成嵌段共聚物自组装的影响
Macromolecules ( IF 5.1 ) Pub Date : 2019-03-14 00:00:00 , DOI: 10.1021/acs.macromol.9b00211
Beihang Yu , Scott P. O. Danielsen , Anastasia L. Patterson , Emily C. Davidson , Rachel A. Segalman

理解非理想聚合物链形状对嵌段共聚物自组装的影响对于设计功能性材料（例如生物聚合物或共轭聚合物）具有可控的自组装行为非常重要。虽然已经显示出嵌段共聚物中的螺旋链形状会产生独特的形态，但是关于链螺旋度如何影响自组装热力学的细节仍然不清楚。在这里，我们利用基于类肽的线圈-螺旋和线圈-螺旋嵌段共聚物模型，通过单体手性和化学性质不变，可以将链的形状从螺旋调整为螺旋。该模型嵌段共聚物体系用于探究链螺旋度对嵌段共聚物自组装热力学的影响。散装材料的小角度X射线散射表明，嵌段共聚物形成了有序的层状结构。线圈-螺旋嵌段共聚物具有相同的畴间距，但显示出较低的有序-无序转变温度（T _ODT）比其线圈线圈类似物。发现线圈-螺旋嵌段共聚物对焓的混合作用较小，这是由在无序状态下测定的较小有效弗洛里-哈金斯相互作用参数（_χeff）所支持的。此外，线圈-螺旋嵌段共聚物的螺旋嵌段在层状形态中经历较大的链拉伸损失，这导致无序化时更大的熵增。焓和熵贡献的共同作用可能降低了螺旋-螺旋嵌段共聚物的T _ODT，使人们对嵌段共聚物自组装中具有非理想形状的聚合物链产生的不同热力学贡献的重要性有了深刻的认识。

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Effects of Helical Chain Shape on Lamellae-Forming Block Copolymer Self-Assembly

Understanding the effects of nonideal polymer chain shapes on block copolymer self-assembly is important for designing functional materials, such as biopolymers or conjugated polymers, with controlled self-assembly behavior. While helical chain shapes in block copolymers have been shown to produce unique morphologies, the details of how chain helicity influences the thermodynamics of self-assembly are still unclear. Here, we utilize model coil–coil and coil–helix block copolymers based on polypeptoids, for which the chain shape can be tuned from helix to coil via monomer chirality with otherwise constant chemistry. This model block copolymer system is used to probe the effects of chain helicity on the thermodynamics of block copolymer self-assembly. Small-angle X-ray scattering of the bulk materials shows that the block copolymers form well-ordered lamellar structures. While having identical domain spacing, the coil–helix block copolymer displays a lower order–disorder transition temperature (T_ODT) than its coil–coil analogue. The coil–helix block copolymer is found to have a smaller enthalpic contribution to mixing, supported by a smaller effective Flory–Huggins interaction parameter (χ_eff) determined in the disordered state. Furthermore, the helical block of the coil–helix block copolymer experiences larger chain stretching penalties in the lamellar morphology, which leads to a larger entropic gain upon disordering. The combined effects of the enthalpic and entropic contributions are likely to have lowered the T_ODT of the coil–helix block copolymer, yielding insight into the importance of different thermodynamic contributions that arise from polymer chains with nonideal shapes in block copolymer self-assembly.

更新日期：2019-03-14

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