含聚3-己基噻吩的嵌段共聚高分子的合成與自組裝之研究 含聚3-己基噻吩的嵌段共聚高分子的合成與自組裝之研究

Abstract

Poly(3-hexylthiophene) (P3HT)之剛-柔嵌段共聚高分子(P3HT BCPs) 經過自組裝可形成規則的奈米結構，使其在有機電子元件的應用上有極大的潛力而受到多方的研究。P3HT BCPs的自組裝行為受到多種因素的影響，包含：剛-剛作用力(rod-rod interaction)、剛-柔作用力(rod-coil interaction)及聚3-己基噻吩之結晶。因此了解P3HT BCPs的自組裝行為對於操控其所形成的微結構與結晶性以提升在元件中的光電性質是極為重要的。在本論文中，我們對於P3HT BCPs 之合成及影響自組裝行為的因素做了系統性的研究。 在第二章中，我們建立一個有效率且可精準控制P3HT BCPs的分子量及組成的合成方法學。本方法學是利用末端改質為醛基之P3HT與軟段的活性陰離子進行高效率的耦合反應(coupling reaction)。我們證明此方法學可以用於多種不同的軟鍊段，如：polystyrene (PS)、polyisoprene (PI) 及 poly(methylmethacrylate) (PMMA) ；並合成出一系列不同組成及分子量的高純度三嵌段共聚高分子。針對這些三嵌段共聚高分子的旋轉塗佈薄膜的研究中，我們發現軟段的化學結構與塗佈所使用的溶劑對於其微結構及吸收光譜有大的影響。 為了使P3HT的結晶性及微結構的連續性同時提升來增加電荷傳輸效率，在第三章中，我們以1,4-addition的polyisoprene (PI(1,4)) 做為P3HT BCP的軟鍊段製備出單邊耦合的poly(3-hexylthiophene-block-isoprene) 雙嵌段共聚高分子(P3HT-b-PI(1,4) DBCP) 與雙邊耦合的poly(isoprene-block-3-hexylthiophene-block-isoprene) 三嵌段共聚高分子 (PI-b-P3HT-b-PI TBCP)。我們針對DBCP 及TBCP的微結構與結晶特性做了系統性的研究。藉由小角度X光散射(SAXS) 及穿透式電子顯微鏡 (TEM) 的觀察，發現PI(1,4) 含量小於40 wt% 的P3HT-b-PI(1,4) DBCP 與PI-b-P3HT-b-PI TBCP 顯出層狀的微結構並有長且直的區域界面。與P3HT homopolymer相比， PI(1,4) 含量小於40 wt%之P3HT-b-PI(1,4) DBCP的P3HT晶粒較大且結晶度更高。我們認為PI(1,4)的高柔軟度及P3HT與PI(1,4)的中度相分離的適度平衡是使其展現出大範圍的規則結構及良好的結晶性的主要因素。此外，高柔軟度的PI(1,4)能夠讓我們藉由對P3HT-b-PI(1,4) DBCP進行簡單的機械摩擦(mechanical rubbing)來產生具有順向性的奈米結構以及良好結晶性的膜材。 在第四章我們研究一系列的雙親性嵌段共聚高分子poly(3-hexylthiophene-block-hydroxylated isoprene) P3HT-b-PIOH DBCPs 與 Poly(hydroxylated isoprene-block-3-hexylthiophene-block-hydroxylated isoprene) PIOH-b-P3HT-b-PIOH TBCPs 的自組裝行為。 合成的方法是藉由將P3HT-b-PI(1,2/3,4) BCPs 的PI鍊段之側鍊雙鍵進行氫硼化-烴基化反應而轉化成為側鍊氫氧基(-OH)。具有高含量PIOH的P3HT-b-PIOH BCPs 在醇類中可形成micelle且被均勻分散。藉由調控混合溶劑的比例可以改變P3HT-b-PIOH BCP 溶液的顏色。在固態中，具有短鍊段PIOH的P3HT-b-PIOH BCPs會形成層狀的微結構，而長鍊段的PIOH的BCPs則形成短柱狀的微結構。由於PIOH鍊段所構成的區域內有分子間氫鍵的存在，因此展現了強相分離的自組裝特性；而微結構的TODT甚至高於250oC ，遠高過P3HT的熔點。當對DBCPs在P3HT的熔融態下進行退火並進行緩慢降溫時，可觀察到P3HT在微相分離的區域內進行受限結晶(confined crystallization)而產生新的相變化。 在第五章中，oxadiazole (OXD)透過酯化反應進行側鍊接枝於P3HT –b-PIOH的PIOH鍊段而得到P3HT-b-POXD p-n半導體嵌段共聚高分子。由 1H NMR 與 GPC 分析可證明此高分子被成功製備。

Poly(3-hexylthiophene) rod-coil block copolymers (P3HT BCP) have drawn significant interests for their potentials in organic electronic applications due to the ability to form order nanostructures through self-assembly, which is complicatedly governed by rod-rod interaction, rod-coil interaction and crystallization of P3HT. Understanding the self-assembly behaviors is critical to manipulate the morphologies of the BCPs and the crystallinity of P3HT domains therein, and thus to improve the optical and electrical properties of the BCPs in the corresponding devices. In this dissertation, systematic studies on syntheses of well-defined P3HT BCPs and factors affecting the self-assembly of selected P3HT BCPs are presented. In chapter 2, an effective methodology was developed to synthesize P3HT BCPs with accurate control on molecular weights and compositions. In this method, P3HT was bi-end-functionalized with aldehyde and which could be coupled with coil segments in living polymeric anions. The coupling reactions were found to be efficient toward various coil segments, including polystyrene (PS), polyisoprene (PI) and poly(methylmethacrylate) (PMMA) to afford P3HT triblock copolymers with a good variation of chemical structures and compositions in high yield and high purity. The further studies on the spin-coated thin films of the resulting P3HT BCPs showed that the coil segments and the solvents noticeablely affect the morphologies and the UV–Vis absorptions. In chapter 3, polyisoprene (PI) was employed as the coil segment in order to achieve simultaneous enhancement in both the domain continuity and P3HT crystallinity for the potential improvement in the device performance by promoting charge transportations. Mono- and bi-end-functionalized P3HT with aldehyde as the terminal group were successfully synthesized in high purity to produce the corresponding Poly(3-hexylthiophene-block-isoprene) diblock copolymers (HT/I(1,4) DBCPs) and Poly(isoprene-block-3-hexylthiophene-block-isoprene) triblock copolymers (HT/I(1,4) TBCPs) through coupling reaction between P3HT and PI anions in 1,4-addition (PI 1,4). Systematic studies on the morphology and the crystallinity of the DBCPs and TBCPs were performed. SAXS and TEM results suggested both DBCPs and TBCPs possessing PI(1,4) < 40 wt% to exhibit lamellae morphology with extended straight inter-domain boundaries. The crystallite size and the degree of crystallization of DBCP with PI(1,4) < 40 wt% were even enlarged as comparing with the corresponding P3HT homopolymers. Thus, the high flexibility and the moderate phase separation between PI(1,4) and P3HT were thought to be responsible to mediate the self-assembly of these BCPs. By incorporating suitable amount of PI(1,4) in DBCPs, the long range order in morphology and the good P3HT crystallinity could be simultaneously achieved. The highly flexible PI enhance the chain mobility significantly at room temperature, allowing the achievement of a highly ordered, uniformly aligned nanostructure with good crystallinity on the P3HT-b-PI possessing a low weight fraction (19.4 wt%) of PI(1,4) via simple mechanical rubbing without the uses of solution based fabrication and thermal treatment. In chapter 4, investigations on self-assembly of amphiphilic P3HT BCPs were carried out for a series of Poly(3-hexylthiophene-block-hydroxylated isoprene) (HT/OH DBCPs) and Poly(hydroxylated isoprene-block-3-hexylthiophene-block-hydroxylated isoprene) (HT/OH TBCPs). Syntheses of HT/OH BCPs were performed via subsequent hydroboration-hydroxylation on the PI segment in 1,2/3,4-addition of P3HT and PI(1,2/3,4) BCPs. HT/OH BCPs with high PIOH content formed micelles and which could homogeneously disperse in alcohols, allowing tuning the color of the HT/OH BCP solution by adjusting the solvent combination. Lamellar morphologies in bulk were observed for both DBCPs and TBCPs with shorter PIOH, while distorted short cylinders were observed for BCPs with higher content of PIOH. The system could be classified as strong segregation as the order disorder transition temperatures were much higher than the melting temperatures of P3HT (TODT > 250oC), which might be attributed to the hydrogen bonding in PIOH domains. Confined crystallization of P3HT within the microdomains of P3HT was observed for the slowly cooled DBCPs, and which was found to generate a new phase transition for P3HT. In chapter 5, we report a single molecule p-n semiconductor was synthesized with the n-type semiconducting oxadiazole (OXD) side chains attached to HT/OH BCPs to afford 3-hexylthiophene and sidechain-oxadiazole HT/OXD BCPs by esterification between acid chloride of oxadiazole moieties and –OH group of PIOH. The 1H NMR and GPC results indicated the success of the synthesis of the polymer.