Springlike nanohelical structures in chiral block copolymers
Springlike nanohelical structures in chiral block copolymers
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DOI：
10.1002/anie.200502236
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Lin, CC
中科院分区：
文献类型：
--
作者：
Chiang, YW;Ho, RM;Lin, CC
螺旋结构可能是自然界中最迷人的形态，由于其在生物结构形成中的特殊功能而受到广泛的研究。螺旋链构象，如单链α螺旋多肽和双链DNADNA，被认为是蛋白质分级组织的基本基序。螺旋结构的形成有多种原因，如氢键、[1]疏溶剂相互作用、[2]π-π相互作用、[3]胆甾相液晶的形成、[4]相对不相容、[5]和手性[6]。在仿生的性质下，通过非共价键相互作用(即二次作用力)，在不同的长度尺度上得到了螺旋形态。由两个化学上不同的组分组成的嵌段共聚物能够自组装成各种有序的纳米结构，如球体、圆柱体、回旋体和片层，这是组成嵌段的不相容的结果。[7]因此，嵌段共聚物中的自组装纳米结构在采用自下而上方法的应用中显得很有前途。[8]与手性分子分级组织中的螺旋超结构不同，螺旋纳米结构是通过由非手性和手性嵌段组成的嵌段共聚物在缓冲液中的自组装获得的，例如聚苯乙烯-b-聚异氰酸酯。在自组装的手性两嵌段共聚物聚苯乙烯-聚(L-丙交酯)(PS-PLLA)中发现了一个三维堆积的纳米螺旋结构相。[9]与两嵌段共聚物的传统相形态相反，纳米螺旋结构相的形成归因于组成PLLA嵌段的手性。[9]此外，热处理后，纳米螺旋相发生了从长螺距到短螺距的显著变化。[10]因此，施加刺激可能会强烈地影响纳米螺旋的结构几何形状。在这里，我们报告了内部和外部的刺激，如结晶和剪切，分别作用于纳米螺旋的形态，使微相分离的PLLA纳米螺旋在PS基质中表现出弹簧行为，以响应所施加的刺激。因此，通过玻璃化、晶化、微相分离和剪切的相互作用，可以获得可切换的纳米结构。通过溶液浇铸PS 280-PLLA 127(FV)制备了嵌段共聚物的块体样品
Helical structures are probably the most fascinating morphologies in nature, and they have been intensively studied as a result of their specific functions in the formation of biological architectures. Helical-chain conformations, such as single-strand α-helical peptides and double-stranded DNA, are regarded as the fundamental motifs for the hierarchical organization of proteins. A variety of origins for the formation of helical structures, such as hydrogen bonds,[1] solvophobic interactions,[2] π–π interactions,[3] cholesteric liquid crystal formation,[4] relative incompatibility,[5] and chirality,[6] have all been demonstrated. Biomimicking nature, helical morphologies have been obtained on different length scales by the interplay of noncovalent bonding interactions (that is, secondary forces). Block copolymers that consist of two chemically different components are able to self-assemble into various ordered nanostructures, such as spheres, cylinders, gyroids, and lamellae, as a consequence of the incompatibility of the constituent blocks.[7] Therefore, the self-assembled nanostructures in block copolymers appear promising in applications that employ the bottom-up approach.[8] In contrast to the helical superstructures in the hierarchical organization of chiral molecules, helical nanostructures have been obtained from the self-assembly of block copolymers that consist of achiral and chiral blocks, for example, polystyrene-b-poly-(isocyanopeptide), in buffer solutions.[6a] However, a threedimensionally packed nanohelical structure phase was found in the self-assembled chiral diblock copolymer, polystyreneb-poly (l-lactide)(PS-PLLA), in the bulk.[9] Contrary to the conventional phase morphology of diblock copolymers, the formation of a nanohelical structure phase is attributed to the chirality of the constituent PLLA block.[9] Furthermore, a significant change, from long-pitch to short-pitch nanohelices, was found in the nanohelical phase upon annealing.[10] Thus, the structural geometries of the nanohelices might be strongly affected by applying stimulation. Herein, we report the internal and external stimuli, such as crystallization and shearing, respectively, which act on the nanohelical morphology so that the microphase-separated PLLA nanohelices exhibit springlike behavior in a PS matrix in response to the applied stimulus. Consequently, switchable nanostructures can be obtained by interplay of vitrification, crystallization, and microphase separation as well as shearing. Bulk samples of block copolymers were prepared by solution casting of PS 280-PLLA 127 (fv