利用不同構形之嵌段式共聚物PS-b-P2VP 製備奈米材料之形態研究

Abstract

嵌段性共聚高分子本身為具有可調控型態與特殊性質的奈米材料，因而具有很高的研究興趣。在本論文中，依照文獻裡的活性陰離子聚合結合連續單體添加法可成功製備線性嵌段型、異相條型星狀以及嵌段型星狀三種不同構形之嵌段性共聚物poly(styrene-2-vinylpyridine) (PSP2VP)。兩種不同自組裝奈米結構在本論文中被探討：(1)嵌段性共聚物-雙親性(PS-b-P2VP/DBSA)小分子複合物(2)利用嵌段性共聚物為孔洞雛形的模版製備奈米級甲基倍半矽氧烷(MSSQ)孔洞材料。 在第一個研究系統中，藉由啶環上的氮可與DBSA 裡的HSO3基團形成分子間鍵結，因此可得到具有等級制的自組裝超分子結構。FTIR實驗中證實了鍵結作用力的存在。所有實驗裡不同構形之嵌段性共聚高分子都居有類似的組成與相對應的分子量，且在未與DBSA形成複合物之前皆具有相同的層狀形態。小角X光散射的結果顯示這些不同等級制的自組裝超分子結構在高溫時除了梳狀結構存在於母體之外，尚具有六方堆積排列的PS柱狀結構。再者，在線性嵌段型PS-P2VP(DBSA)複合物、異相條型星狀H-PS-b-P2VP(DBSA)複合物中，從層狀到柱狀的形態改變時，規則區域間的距離並沒有很大的改變，但是在嵌段型星狀B-PS-b-P2VP(DBSA)複合物系統裡則是看到明顯大量的減少。而在不同系統中，規則-不規則過渡區亦有明顯的不同。嵌段性星狀B-PS-b-P2VP(DBSA)複合物具有最低的過渡溫度，而異相條型星狀H-PS-b-P2VP(DBSA)複合物則是最高，這些現象可解釋為因為星狀高分子裡核的位置不同所造成，嵌段性星狀的核位於PS區域間，而異相條型星狀的核在介面上，核的位置不同將造成高分子鏈段具有類似非高斯伸展的運動過程。 在第二個研究中，由於氫鍵、離子鍵存在於MSSQ與PS-b-P2VP裡，因此可避免在熱處理前的大規模相分離，而只存在微觀的小區域。可行成自組裝微相結構的PS-b-P2VP將會藉由高溫處裡的過程移除，而留下奈米級的孔洞。本研究提出兩種製備孔洞材料的方式: 蒸發引導自組裝之熱乾燥與沈浸式塗布製程。前者可製備塊狀材料，後者可製備薄膜。孔洞塊狀材料的形態藉由SAXS與TEM作分析；得到結果是：藉由此製程所得的孔洞材料排列規則。另一方面，以FE-SEM、TEM、AFM分析鑑定孔洞薄膜材料的特性；在以異相條型星狀與線性嵌段型做為模版得到的孔洞大小，依照高分子的含量約在17-22nm：另一方面，以嵌段型星狀做為模版得到所得到的結果中，在高分子含量50%時會出現互相連接的孔洞群，此原因可能來自於在製備嵌段型星狀高分子的過程中，不易控制的特性而得到較大的分子量分布。 上述研究顯示，嵌段型共聚物的構形在控制奈米級衍生物扮演極為重要的角色。

Block copolymers have stimulated significant scientific interest since they offer the possibilities to nanoscale materials with tunable morphology and properties. In this thesis, linear diblock copolymer polystyrene-block-poly(2-vinyl pyridine) (L-PS-b-P2VP), heteroarm star copolymer H-PS-b-P2VP, and blockarm star copolymer B-PS-b-P2VP, were successfully synthesized by living anionic polymerization. Then, the different architectures of the PS-b-P2VP were used to prepare two different types of self-assembled nanostructures: (1) block copolymer-amphiphile complexes (PS-b-P2VP/DBSA); (2) mesoporous methylsilsesquioxane (MSSQ) materials using PS-b-P2VP as templates. The experimental results showed that intermolecular bonding existed between the nitrogen of the 2-VP ring and the HSO3 or DBSA. Thus, the hierarchical self-organized supramolecules were obtained from the PS-b-P2VP/DBSA complexes. All the PSP2VP copolymers with a similar composition and molecular weight have lamellar morphology in the neat state. On complexation with the DBSA, the SAXS profiles suggests the formation of the hierarchical structures consisted of hexagonally packed PS cylinders in the P2VP(DBSA) lamellar morphology at a high temperature. The interdomain distance in the H-PS-b-P2VP(DBSA) and L-PS-b-P2VP(DBSA) complexes does not change significantly as the morphology change from lamellae to cylinder by complexation, but that in the B-PS-b-P2VP(DBSA) complexes shows a significant decrease. Besides, the order-disorder transition also varies significantly in the complexes of different architectures. The B-PS-b-P2VP/DBSA complex has the lowest TODT whereas the H-PS-b-P2VP/DBSA complex has the highest TODT, which is probably due to the difference on the polymer architecture. The central cores in blockarm and heteroarm block copolymers are located inside the microdomain and at the interface, respectively, which results in different degree of non-gaussian chain stretching in these copolymers. In the second topic of the thesis, nanoporous MSSQ films were prepared through the templating of PS-b-P2VP using the processes of evaporation-induced self-assembly dry-casting (for bulk materials) and dip-coating(for thin film). Hydrogen-bonding and ionic bonding interaction between the MSSQ precursors and PSP2VP prevents large-scale phase-separation before thermal treatment. Upon thermal curing, the self-condensation between the MSSQ end group results in the microphase separation between the MSSQ and PSP2VP. The self-organized PSP2VP was removed by thermal curing and left nano-pores in the MSSQ matrix. Morphologies of bulk materials were characterized preferentially using SAXS and TEM. Ordered porous thin films were observed from the images of the FE-SEM, TEM, and AFM. The pore size prepared from the cases of the MSSQ/L-PS-b-P2VP or H-PS-P2VP are in the range of 17 to 22 nm, depending on the PS-b-P2VP loading (30% ~ 50%). However, the MSSQ/B-PS-b-P2VP results in small discrete pores to connected metamorphic pores at polymer loading of 50 wt%, which could be due to the large polydispersity of the B-PS-b-P2VP. The experimental result in this thesis suggests that the architecture of the block copolymers plays a very important role on controlling the morphologies of the resulted nanostructured derivatives.