Molecular Foundry, ‡Materials Sciences Division, ∥Environmental Energy Technologies Division, and #National Center for Electron Microscopy, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
J Am Chem Soc. 2013 Sep 25;135(38):14119-24. doi: 10.1021/ja404233d. Epub 2013 Sep 16.
Microphase-separated block copolymer materials have a wide array of potential applications ranging from nanoscale lithography to energy storage. Our understanding of the factors that govern the morphology of these systems is based on comparisons between theory and experiment. The theories generally assume that the chains are perfectly monodisperse; however, typical experimental copolymer preparations have polydispersity indices (PDIs) ranging from 1.01 to 1.10. In contrast, we present a systematic study of the relationship between chemical structure and morphology in the solid state using peptoid diblock copolymers with PDIs of ≤1.00013. A series of comb-like peptoid block copolymers, poly(N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine)-block-poly(N-(2-ethylhexyl)glycine) (pNte-b-pNeh), were obtained by solid-phase synthesis. The number of monomers per chain was held fixed at 36, while the volume fraction of the Nte block (ϕNte) was varied from 0.11 to 0.65. The experimentally determined order-disorder transition temperature exhibited a maximum at ϕNte = 0.24, not ϕNte = 0.5 as expected from theory. All of the ordered phases had a lamellar morphology, even in the case of ϕNte = 0.11. Our results are in qualitative disagreement with all known theories of microphase separation in block copolymers. This raises new questions about the intertwined roles of monomer architecture and polydispersity in the phase behavior of diblock copolymers.
微相分离嵌段共聚物材料具有广泛的潜在应用，从纳米光刻到储能。我们对这些体系形态控制因素的理解是基于理论和实验之间的比较。这些理论通常假设链是完美的单分散的；然而，典型的实验共聚物制备具有多分散指数（PDI）在 1.01 到 1.10 之间。相比之下，我们使用 PDI 小于等于 1.00013 的聚肽二嵌段共聚物对化学结构和固态形态之间的关系进行了系统研究。一系列梳状聚肽嵌段共聚物，聚（N-2-（2-（2-甲氧基乙氧基）乙氧基）乙基甘氨酸）-嵌段-聚（N-（2-乙基己基）甘氨酸）（pNte-b-pNeh），通过固相合成获得。每条链的单体数固定在 36 个，而 Nte 块的体积分数（ϕNte）从 0.11 变化到 0.65。实验确定的无序-有序转变温度在 ϕNte = 0.24 时出现最大值，而不是理论预期的 ϕNte = 0.5。所有有序相都具有层状形态，即使在 ϕNte = 0.11 的情况下也是如此。我们的结果与所有已知的嵌段共聚物微相分离理论在定性上不一致。这引发了关于单体结构和多分散性在嵌段共聚物相行为中相互交织作用的新问题。
