不同分子結構芴系硬桿-柔軟嵌段共聚物:合成、型態與光物理性質之研究

Abstract

共軛硬桿-柔軟嵌段共聚物因其自組裝的特性可運用於奈米電子元件或多功能元件上而廣受注目。目前為止硬桿-柔軟雙嵌段共聚物的自組裝行為多著重於線性雙嵌段及三嵌段共聚物。先前本實驗室已經發表多種硬桿-柔軟嵌段共聚物的合成，型態與性質之研究，其中包含聚芴-聚乙烯吡啶硬桿-柔軟嵌段共聚物。然而諸如星狀嵌段或是側鏈硬桿等不同分子結構對於此類嵌段共聚物的影響之相關研究至今仍未趨完善。故本論文之研究目標著眼於合成二種不同結構芴系硬桿-柔軟嵌段共聚物，包括星狀嵌段共聚物及側鏈芴系雙嵌段共聚物，並探討不同高分子結構與其微結構型態對於光電性質之影響。 在第一部份(第二章)，首先結合鈴木偶合反應及活性陰離子聚合法製備硬桿-柔軟聚芴-聚乙烯吡啶雙嵌段活性鏈；接著加入二甲基丙烯酸乙二醇酯使其交相聯接成硬桿-柔軟聚芴-聚乙烯吡啶星狀嵌段共聚物。我們利用動態光散射儀及原子力顯微鏡分析此二種不同結構共聚物於不同體積比的四氫呋喃/甲醇混合溶液下之聚集型態，佐以紫外可見光光譜儀及光激發螢光光譜探討其微結構對於光電性質的影響。由實驗結果得知，於不同體積比的四氫呋喃/甲醇混合溶液下雙嵌段共聚物在甲醇漸增時其微結構由球形微胞轉變成膜泡，然而具對稱結構的星狀嵌段共聚物在甲醇漸增時卻維持微胞結構。此外，對於雙嵌段共聚物而言，隨著甲醇於四氫呋喃/甲醇混合液中的含量增加促使聚芴鍊段產生H形態聚集，導致其在吸收及光激發螢光光譜產生藍移；然而星狀嵌段共聚物在增加甲醇含量時其吸收光譜並無位移但光激發螢光光譜卻紅移，意指星狀嵌段共聚物具有不同於雙嵌段共聚物的聚集。而星狀嵌段共聚物的光量子效率相對於雙嵌段共聚物而言更是嚴重地被抑制。此外，雙嵌段及星狀嵌段共聚物的薄膜因聚芴鏈段的分子間交互作用力導致光激發螢光光譜紅移。 在第二部份(第三章)，我們結合原子轉移自由基聚合法及鈴木偶合反應製備具不同鏈段長的側鏈芴系聚乙烯吡啶-聚芴苯乙烯雙嵌段共聚物。此法的優點在於可製備具高分子量的聚芴苯乙烯嵌段，並有多樣的柔軟鏈段可選擇做為第二嵌段。經由改變嵌段長度可使聚乙烯吡啶-聚芴苯乙烯共聚物具有不同的光物理性質。當聚乙烯吡啶的莫耳分率增加時，吸收光譜會藍移，這可能是長鏈段的聚乙烯吡啶會抑制芴官能基的次序使得有效共軛長度減短所致。而且具有長聚芴苯乙烯嵌段的共聚物因其具有高含量的芴官能基與不同共軛長度分佈從而使光激發螢光光譜較為寬廣。 綜觀上述研究，不同的高分子結構會導致芴系硬桿-柔軟嵌段共聚物具有不同的微相分離型態並明顯轉換其光物理性質。

Conjugated rod-coil block copolymers have attracted extensive research activity because of their self-assemblied characteristics for nanoelectronic or multifunctional device applications. Up to now, most studies of the self-assembly of rod-coil block copolymers are focused on linear diblock and triblock copolymers. Previously, our laboratories have explored the synthesis, morphologies, and properties of several conjugated rod-coil block copolymers, including polyfluorene/poly(vinylpyridine) rod-coil block copolymers. However, the effects of molecular architecture on such block copolymers have not been fully explored yet, such as star block structures or side-chain rod grafting. In this study, we explore the synthesis, morphologies and properties of two fluorine based rod-coil block copolymers, including star-shaped polyfluorene-b-poly(2-vinylpyridine) (PF-b-P2VP)n and poly(2-vinyl pyridine) -b-poly(styrene-fluorene) (PStFl-b-P2VP). In 1st part (Chapter 2), rod-coil PF-b-P2VP diblock copolymers containing conjugated poly[2,7-(9,9-dihexylfluorene)] (PF) and coil-like poly(2-vinylpyridine) (P2VP) were first synthesized by combining Suzuki coupling reaction and living anionic polymerization. Then, (PF-b-P2VP)n star-block copolymers were prepared by adding coupling reagent EGDMA to cross-link living anionic PF-b-P2VP arms together. The main architectural difference between diblock and star-block copolymers resulted in a significant variation on their morphologies and photophysical properties. The experimental results showed that PF-b-P2VP diblock copolymers varied from spherical micelles to vesicles with increasing methanol content in THF/methanol mixtures. However, (PF-b-P2VP)n star-block copolymers with a symmetric architecture maintained spherical micelles as the methanol content increased. The effects of micellar morphologies on photophysical properties were investigated by optical absorption and photoluminescence (PL). For PF-b-P2VP diblock copolymers, the increase of the methanol content induced a blue shift in both absorption and emission spectra, suggesting an “H-type” aggregation. However, (PF-b-P2VP)n star-block exhibited no shift in absorption but a red shift in emission spectra by increasing the methanol content, reflecting a different type aggregation against diblock analogue. The quantum efficiencies of (PF-b-P2VP)n star-block copolymers quenched more seriously than diblock ones as increasing the methanol content in THF/methanol mixtures. Besides, the existence of interchain interactions for PF blocks inducing a red shift of emission spectra in thin films for both diblock and star-block copolymers. In 2nd part (Chapter 3), the combination of atom transfer radical polymerization (ATRP) and Suzuki coupling reaction was used to synthesize P2VP-b-P(St-Fl) diblock copolymers. The advantage of this method is that we can prepare block copolymers with higher molecular weight of P(St-Fl) and choose a variety of coil segment as second block. Side chain fluorene-based P2VP-b-P(St-Fl) diblock copolymers showed a significant variation on photophysical properties through adjusting the block length. As the molar ratio of P2VP (coil) block increased, the optical absorption peak had a blue shift. It indicated that the incorporation of long P2VP block inhibited the aggregation of the fluorene moieties and reduced the effective conjugated length of P(St-Fl). Both P2VP79-b-P(St-Fl)347 and P2VP140-b-P(St-Fl)138 had high fluorene moieties content and different conjugated length distribution, which led to broader photoluminescence spectra than P2VP140-b-P(St-Fl)15. The aforementioned results suggest that various morphologies can be efficiently manipulated by polymer architecture and lead to significantly tuning on the phtophysical properties.