不同構形嵌段共聚物系統-合成、形態及其特性應用:PS-b-P4VP及PF-b-P2VP

Synthesis, Morphology, and Applications of Block Copolymers with Different Architectures:PS-b-P4VP and PF-b-P2VP

林佳宏(Chia-Hung Lin)

指導教授 ： 陳文章

國立臺灣大學/工學院/化學工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.01081

摘要

在當代巨分子科學領域中，嵌段共聚物是眾多研究工作中的焦點，這歸因於其一系列吸引人的基礎問題，這些問題伴隨著暸解其在溶液及固態的自組裝過程；嵌段共聚物呈現出一個具有廣泛研究重點的主題，這些主題跨越了巨分子化學與物理：包括新合成方法的開發、製備不同構型的共聚物、電腦的理論模擬、自組裝行為與形態的研究及共聚物的應用......等；本研究論文的目標為對於高分子科學中嵌段共聚物的物理與化學性質提供有益的瞭解，本論文研究的重點可以簡述如下，包括對於具有線性及非線性(星狀)之雙親性柔軟-柔軟及共軛性硬桿-柔軟嵌段共聚物的合成、自組裝結構及物理性質探討，及共軛性硬桿-柔軟嵌段共聚物於電紡技術的應用。這些研究主題將於下段開始再進一步描述。
在第一部份(第二章)，新型雜臂星狀雙親性共聚物:polystyrene-b-poly(4- vinylpyridine) (PS-b-P4VP)以陰離子活性聚合法製備出四種不同共聚莫耳比例的樣品；這些共聚物於溶液中在不同構形、選擇性溶劑含量、共同溶劑的極性及不同共聚比例的微胞結構被探討。我們使用動態/靜態光散射儀(DLS/SLS)、穿透式電子顯微鏡(TEM)及原子力顯微鏡(AFM)分析微胞的結構；從實驗結果得知，在DMF/H2O的混合溶劑環境中，星狀共聚物的聚集尺寸及微胞中分子鏈數目均小於其相似比例的線性共聚物，而星狀共聚物的聚集結構也被觀察到當選擇溶劑含量的增加其有了從球狀到柱狀、空心球狀及聚集的空心球狀的轉變。除此之外，當共聚物於DMF/H2O或1,4-dioxane/H2O呈現球狀時，其卻於THF/H2O中呈現大的聚集微胞結構，這是因為PS鏈段在不同溶液環境中有不同的伸展程度。當P4VP鏈段於共聚物中的莫耳比例由0.37降到0.24、0.12及0.07時，其微胞結構呈現了球狀與柱狀混合、空心球狀、巨大空心球狀及大的聚集微胞等不同結構，這些不同結構的原因乃歸因於核心鏈段不同的伸展程度所致。因此，此研究證明了聚合物構形對於聚集行為的影響及星狀共聚物於溶液下可以藉由改變調整溶劑極性及共聚鏈段比例而得到多元的微胞聚集結構。
在第二部份(第三章)，新型硬桿-柔軟雙嵌段式及三嵌段式包含硬桿鏈段為poly(2,7-(9,9-dihexylfluorene))(PF)及柔軟鏈段為poly(2-vinylpyridine) (P2VP)的共聚物以結合耦合反應及陰離子聚合法製備；我們使用原子力顯微鏡(AFM)、穿透式電子顯微鏡(TEM)、動態光散射儀(DLS)及冷凍穿透式電子顯微鏡(cryo-TEM)分析共聚物於不同比例的MeOH/THF混合溶液下之聚集結構，微胞結構對於光電性質的影響將以UV-vis 光吸收及PL光放射光譜圖探討。由實驗結果得知，雙嵌段式共聚物PF-b-P2VP於MeOH比例增加時維持其球狀形狀，然而，三嵌段式共聚物P2VP-b-PF-b-P2VP卻在MeOH增加時聚集成柱狀結構，這是歸因於其對稱性構形；因此，P2VP-b-PF-b-P2VP的共軛部份相較於PF-b-P2VP有較高程度的π-π排列，這導致P2VP-b-PF-b-P2VP有較高的吸收峰位置，而光量子效率會隨著MeOH的增加而逐漸被抑制；除此之外，對於PF-b-P2VP而言，MeOH的增加會導致其在吸收及放射光譜圖有藍位移的現象發生，這被稱為“H-型”的聚集，然而，P2VP-b-PF-b-P2VP卻同樣在增加MeOH的含量時呈現出吸收光譜藍位移及放射光譜紅位移的現象，這反映出其具有不同形式的聚集。本篇研究發現了共軛型硬桿-柔軟嵌段共聚物的不同高分子構形及聚集結構對於及光物理性質的影響。
在第三部份(第四章)，我們發展出一個發法製備新型的星狀硬桿-柔軟共聚物poly(2,7-(9,9-dihexylfluorene))-b-poly(2-vinylpyridine) (star-PF-b-P2VP)，這個方法藉由參考前一章陰離子法製備線性雙嵌段式PF-b-P2VP而近一步交相聯接具有活性陰離子末端的PF-b-P2VP。星狀共聚物於旋轉塗佈薄膜的結構將藉由原子力顯微鏡(AFM)分析，熱處理、載台性質、高分子初始濃度及混合溶液的比例等變因被應用於研究可調控的聚集結構，為了更近一步瞭解共聚物的聚集行為，微結構的型態結果將結合PL光放射光譜一同討論，星狀共聚物薄膜在當PF π-π排列程度上升時呈現出放射光譜紅位移的現象；比較線性雙嵌段式及星形共聚物於溶液下的聚集結果，星狀共聚物呈現出不同的聚集行為，這兩者的差異也被歸因於對稱/非對稱構形的影響結果。
在第四部份(第五章)，靜電紡絲纖維藉由使用共軛型硬桿-柔軟雙嵌段式及三嵌段式共聚物PF-b-P2VP 及 P2VP-b-PF-b-P2VP混掺合的混合物被研究其形態及光電性質，良好成形的電紡絲藉由場發射掃描式電子顯微鏡(FE-SEM)及穿透式電子顯微鏡(TEM)確認，所有樣品在螢光顯微鏡(Confocal)呈現出均勻的藍光纖維結構。纖維在由MeOH/H2O製備的管徑約為600-1000奈米, 而由CHCl3 製備的粗細則在幾微米左右, 此製備粗細不同是因為兩個溶劑介電常數不同所致。PF 聚集的區塊隨者共聚物含量的增加而加大。在低分子量PEO(Mn~100,000)的混掺系統中(雙嵌段及三嵌段系統)， 纖維在PL放射光譜中相對於薄膜時有紅位移的現象,但在高分子量PEO(Mn~2000,000)的混掺系統中，纖維與薄膜則有差異不大的放射光譜位置。另外，PF的聚集區塊尺度被發現在雙嵌段混掺系統中比三嵌段混掺系統中來的大，此表示了共聚物構形的重要性。

關鍵字

嵌段式共聚物 ； 形態 ； 共軛高分子 ； 硬桿-柔軟 ； 構形 ； 陰離子聚合

並列摘要

Block copolymers have attracted extensive research activity in contemporary macromolecular science. This is attributable to a range of fascinating fundamental issues associated with understanding self-assembly processes in both solution and in bulk. One of the main issues on block copolymers requires further exploration is the polymer architecture effect, especially on the conjugated rod-coil systems. The research objectives of this thesis are to explore the synthesis, morphology (solution, film, or fiber), and properties of block copolymers with different polymer architecture, including coil-coil, rod-coil, coil-rod-coil, and star block structures. The following summarize the important discovery of this thesis.
In 1st part (Chapter 2), new hetero-arm star amphiphilic block copolymers of polystyrene-block-poly(4-vinylpyridine) (PS4-P4VP4) with four different mole ratios of 4VP moiety (f4VP) were synthesized by sequential living anionic polymerization. Micellar morphologies of the synthesized copolymers in dilute solution were explored through the variation of polymer architecture, selective solvent content, common solvent polarity, and block ratio. Dynamic/static light scattering (DLS and SLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to characterize the micellar morphologies. The experimental results suggested that the aggregation size and number of PS4-P4VP4 solution micelles were smaller than those of the linear analog. Morphological transformation of hetero-arm PS4-P4VP4 from spheres to cylinders, vesicles, and large compound vesicles was observed as the water content increased. The morphology of PS4-P4VP4 in the solvent mixture of DMF/water or 1,4-dioxane/water was shown sphere but changed into large compound micelles in the THF/water due to the different degree of swelling on the PS block. As the P4VP molar ratio decreased from 0.37 to 0.24, 0.12 and 0.07, the morphology changed from spherical mixed with cylindrical, to vesicles, giant vesicles, and then to large compound micelles due to the core chain stretching.
In 2nd part (Chapter 3), new rod-coil diblock and coil-rod-coil triblock copolymers containing conjugated poly[2,7-(9,9-dihexylfluorene)] (PF) and coil-like poly(2-vinylpyridine) (P2VP) were synthesized by combining coupling reaction and living anionic polymerization. The experimental results showed that the diblock PF-b-P2VP maintained spherical micellar aggregates as the methanol content increased. However, the triblock P2VP-b-PF-b-P2VP were found to readily aggregate in elongated cylinders due to its symmetric structure. Consequently, P2VP-b-PF-b-P2VP polymer chains could stack together favorably and have stronger π-πinterchain compared with diblock PF-b-P2VP, leading to the higher absorption maximum. The quantum efficiencies were gradually quenched with increasing the MeOH content for both copolymers. Moreover, for diblock PF-b-P2VP, the increase of the MeOH content induced a blue shift in both absorption and PL spectra, suggesting an “H-type” aggregation. However, triblock P2VP-b-PF-b-P2VP exhibited a blue shift in absorption but a red shift in PL by increasing the MeOH content, which reflected a different type of aggregation.
In 3rd part (Chapter 4), we developed the synthetic routine for preparing new rod-coil star-like poly[2,7-(9,9-dihexylfluorene)]-block-Poly(2-vinylpyridine) block copolymer (star-PF-b-P2VP) by cross linking of living anionic PF-b-P2VP chain ends, according to synthetic concepts of preparation of diblock PF-b-P2VP. The morphologies of the copolymers in spin-coated thin films were analyzed via atomic force microscopy (AFM). The annealing treatment, substrate, initial polymer concentration and mixed solvent effects are applied to research to obtain tunable aggregated structures. In order to gain further insight of aggregation behavior, the morphological results are then combined with photoluminescence spectra (PL). By comparing the experimental results with diblock PF-b-P2VP copolymers in solution, star copolymers exhibit different aggregation behavior due to symmetric/asymmetric architectures for two kinds of architectures.
In 4th part (Chapter 5), morphology and photophysical properties of electrospun (ES) nanofibers prepared from the blends of conjugated rod-coil diblock PF-b-P2VP and triblock P2VP-b-PF-b-P2VP copolymers with PEO were studied. Well-produced ES fibers are confirmed by field-emission scanning microscopy (FE-SEM) and transmission electron microscopy (TEM), and uniform blue emission is appeared in confocal images for all samples. The prepared ES fiber diameters were around 600-1000 nm using the processing solvent of MeOH/H2O while those from CHCl3 were a few thousands of nm, due to the difference on the dielectric constant. The PF aggregation domain increased with enhancing the block copolymer composition in the ES fibers. In copolymer/low Mw of PEO (Mn~100,000) blending system, it has red-shifting of emission peak from fibers to films, which is different from high Mw of PEO (Mn~2,000,000) blending system, displaying no obvious shifts of emission peaks between films and fibers in both diblock and triblock systems. Furthermore, the PF aggregated domain was larger in the PF-b-P2VP/PEO ES fibers than that of P2VP-b-PF-b-P2VP and led to much reduced aggregation emission, which suggested the importance of polymer architecture.

並列關鍵字

block copolymer ； morphology ； conjugated polymer ； rod-coil ； architecture ； anionic polymerization

參考文獻

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