末端修飾電活性苯胺五聚體的兩性聚醯胺規則型樹枝狀高分子之合成及性質研究

Synthesis and Properties of Amphiphilic Poly(amidoamine) Dendrimers with an Aniline Pentamer Shell

洪偉毅(Wei-I Hung)

指導教授 ： 葉瑞銘

中原大學/理學院/化學研究所/博士(2011年)

https://doi.org/10.6840/cycu201100390

摘要

本研究合成第二代到第五代末端修飾苯胺五聚體的聚醯胺樹枝狀高分子，實驗發現電活性樹枝狀高分子的氧化、還原與摻雜、去摻雜等行為與樹枝狀分子PAMAM的代數在不同酸、鹼環境下有著密切的關係。以PAMAM G2為例，研究中可以發現苯胺五聚體中苯環π–π*的吸收峰從中性環境到鹼性環境下會有明顯的紅位移，此有可能是因為PAMAM G2的尺寸變小而末端苯胺五聚體相互靠近所導致。而電活性樹枝狀分子的化學氧化過程與顏色改變可以藉由循環伏安與電致變色所觀察得到，所有的樹狀分子皆出現三對的氧化還原峰，且電流密度會隨著代數上升後表面苯胺五聚體變多而逐漸升高，在電致變色部份則會因為調整電位而得到不同顏色的改變。在熱性質方面，因為末端修飾上結構較剛硬的苯胺五聚體，所以會提升整體樹枝狀分子的熱穩定性。
苯胺五聚體同樣可視為一疏水性的分子，因此末端修飾苯胺五聚體的樹枝狀高分子具有兩性結構，此結構無論在低代數或高代數下，在水溶液中皆可形雙層膜的囊泡聚集體。在中性環境下，囊泡的大小會隨著代數的上升而逐漸下降，而臨界聚集濃度同樣會因為代數上升後更能穩定存在。經穿透式電子顯微鏡觀察可得到，以樹枝狀分子為主的囊泡會因為親水性的枝狀層分布在囊泡外層，並藉由氫鍵作用而相互粘連。此外，研究中更進一步探討不同代數的雙層膜聚集體在不同酸、鹼環境下的型態及大小關係，研究發現，在鹼性環境下，苯胺五聚體間的π–π作用力增加，導致囊泡聚集更明顯，而在酸性環境下則會因為聚醯胺樹狀分子產生四級胺鹽而造成結構鬆散。最後由廣角X-ray繞射儀得知，末端修飾苯胺五聚體的高代數樹枝狀高分子，因苯胺五聚體間存在強大的π–π作用力，可使兩性樹狀分子產生具有組裝的驅動力。

關鍵字

聚醯胺樹枝狀高分子 ； 苯胺五聚體 ； 自組裝 ； 電活性性質 ； 兩性結構

並列摘要

Poly(amidoamine) (PAMAM) dendrimers with different generations (G = 2, 3, 4 and 5) have been peripherally modified with aniline pentamers (AP). Their redox and dopable behavior are strongly affected by the dendritic architectures at different generations under different pH conditions. It was found that the electron transition of the πB–πQ band red-shifted and the size of PAMAM G2 decreased in an alkaline medium. The chemical oxidation process and the color change of these modified dendritic macromolecules were measured by cyclic voltammetry (CV) and electrochromism. All of the dendrimers showed three redox peaks in the CV. The current density of the voltammograms increased with increasing the number of aniline pentamer segments at the periphery. A drastic color change was observed when a linear potential sweep was applied. From thermal properties of the electroactive dendrimers, it reveals the introduction of electroactive AP on PAMAM dendrimers can improve the thermal stability of the dendrimers.
These amphiphilic PAMAM dendrimers peripherally modified with hydrophobic AP shell can self-assemble into vesicular bilayer aggregates at lower (G2 & G3) and higher (G4 & G5) generations in water. The size of these vesicles are decrease with increasing generation under neutral pH. Critical aggregation concentration reveals that these aggregates can be favorably formed in the order of G5 ＞G4 ＞ G3 ＞ G2. These dendrimer-based vesicles are very adhesive due to the H-bonding interaction and entanglement of dendritic branches located in the outer layer. In addition, the different morphology and size of the bilayer assemblies have great influence on pH values of ~ 3, 7, and 9. The high pH form has a strongly π–π interaction between APs, whereas ion pairing at low pH leads to a loose structure of dendritic branches located in the outer layer, which can identifiable with transmission electron microscopy (TEM) images with negative staining. WAXRD experiments indicated that the higher generations of amphiphilic dendrimers are more order owing to APs exhibit a powerful driving force for the self-assembly.

並列關鍵字

poly(amidoamine) dendrimers ； aniline pentamer ； electroactive properties ； amphiphilic structure ； self-assembly

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