|Abstract: ||在自然界中，螺旋形態可能是最迷人的自組裝結構之一。本實驗擬利用掌性分子的非共價鍵自組裝行為來探討在不同層級之螺旋形態間的相依關係。先前的研究證實具有立體規則的乙烯基聚合物，聚(2-乙烯基?啶) (poly(2-vinyl pyridine),P2VP)可利用掌性摻雜物之錯化呈現誘導圓二色特性(Induced Circular Dichroism, ICD)。此外ICD的強弱變化將取決於P2VP的同排立體規則度。本研究目的為探討聚（2-乙烯基?啶）(iP2VP)與L-和D-扁桃酸(Mandelic Acids)混摻後之自組裝行為。首先在薄膜狀態下將iP2VP與掌性酸混合，由對應之ICD訊號顯示螺旋構型的形成可利用扁桃酸與?啶環之結合來實現。同時發現具有扁桃酸之iP2VP於薄膜狀態結晶後，於偏振光顯微鏡(Polarized Light Microscopy, PLM)下呈現帶狀球晶型態推論其旋轉具有特定的左右旋性，其成因乃是結晶層板上下表面應力不平衡所致，進而導致結晶層板的扭轉最重要的是將促使其旋轉具有特定的左右旋性。換言之，可利用加入的掌性扁桃酸來控制iP2VP結晶層板成長之旋性。結果顯示此種誘導掌性之效應可由分子層級開始，傳遞到相層級。|
同時本研究亦進行此類具有ICD之嵌段共聚物的自組裝行為。探討，以期瞭解同掌性傳遞於微相分離的實際效應。首先合成出柱狀聚苯乙烯-聚（2-乙烯基?啶）(PS-b-iP2VP)嵌段共聚物，以進行類似前述ICD效應之探討。由穿透式電子顯微鏡(Transmission Electron Microscopy ,TEM)與小角度X射線散射(Small-Angle X-ray Scattering ,SAXS)實驗結果證實PS-iP2VP與扁桃酸結合後可自組裝形成有序螺旋結構相。
Among self-assembled architectures, helical morphology is probably the most fascinating texture in nature. By introducing the chirality into synthetic molecules, helical textures on different length scales can be obtained by self-assembling through interplay of secondary interactions (i.e., non-covalent bonding forces). Our previous studies demonstrated that induced circular dichroism (ICD) of stereoregular vinyl polymers, poly(2-vinyl pyridine)s (P2VPs) can be driven by association of chiral dopant, suggesting the formation of helical polymer chain with exclusive handedness. The ICD via the association with chiral acids strongly depends upon the isotacticity of the P2VPs. In this study, we aim to examine the self-assembled behaviors of isotactic poly(2-vinyl pyridine) (iP2VP) with L- and D-mandelic acids (MA) as chiral dopants. For the iP2VP complexing with the chiral acids in the film state, mirror image of the corresponding ICD indicates that the formation of preferential helical conformation can be achieved by complexation of chiral dopants with pyridine. Most interestingly, bands spherulites (the presence of concentric rings or extinction bands under polarizes light microscope (PLM) observations) can be formed in the film state by crystallization of the iP2VPs with chiral dopants, providing a model system for the examination of the chirality transfer from conformational chirality to hierarchical chirality. Controlled handedness of crystalline lamellae in the banded spherulites can be found in crystallized iP2VP with chiral MA. Owing to the crystalline lamellar twisting, resulting from imbalanced stresses at the opposite folding surfaces, the preferential sense of the lamellar twisting can be determined using polarized light microscopy (PLM). As a result, homochiral evolution from molecular chirality to hierarchical chirality can be found in the crystallized iP2VP with ICD.
In contrast to the homochiral evolution in crystallized iP2VP, we are also interested in the chirality transfer of self-assembled block copolymers (BCPs). A series of polystyrene-b-poly(isotactic 2-vinyl pyridine) (PS-iP2VP) with cylinder-forming phase are synthesized for the examination of the homochiral evolution on BCP self-assembly through the ICD. Helix-like transmission electron microscopy (TEM) projections can be observed in the PS-iP2VP complexing with the chiral dopants (i.e., MA). On the basis of small-angle X-ray scattering experiments, those helices can be found to appear as hexagonally packed lattice. As a result, helical phase is identified for the self-assembled PS-iP2VP/R- or S-MA, suggesting the chirality effect on the self-assembly of the PS-iP2VP/R- or S-MA. To further examine the homochiral evolution, the ICD behaviors of the PS-iP2VP driven by the introduced enantiomeric MA are examined by CD, and similar mirror-imaged results can be found. With the examination of the handedness of forming helical phase, a methodology for the examination of the homochiral evolution in the BCPs with ICD is suggested.