含聚3-烷基噻吩之硬桿-柔曲和硬桿-硬桿團聯共聚高分子的合成與自組裝行為的研究

Synthesis and Self-Assembly of Poly(3-alkylthiophene)-containing Rod-Coil and Rod-Rod Block Copolymers

林詩翔(Shih-Hsiang Lin)

指導教授 ： 林唯芳

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.11105

摘要

摘要
近年來，因為有機光電元件(organic optoelectronics)的輕、薄、可撓曲、低成本且可大面積製備等優點，已引起研究人員的廣泛注意。控制有機光電元件材料的形態具有規整的結構，並將其予體(donor)和受體(acceptor)材料所形成的區域尺寸控制在10奈米左右，將是達到高效率有機光電元件的關鍵因素之一。利用團聯共聚高分子(block copolymer)獨特的自組裝行為來達到這個目的，是非常有潛力的一種方法。對於典型柔曲-柔曲(coil-coil)團聯共聚高分子而言，藉由改變某一鏈段高分子的體積分率，而得到非層狀且具有連續相的結構，已是很成熟的技術，但這方法對於硬桿-柔曲(rod-coil)團聯共聚高分子而言，卻不總是有效。此外，若使用柔曲-柔曲團聯共聚高分子來當作元件中光反應層的材料，受限於其絕緣的性質，將無法有效地提升元件的表現。所以，在本研究中，已成功地利用速配接合化學(click chemistry)來製備poly(3-alkylthiophene)-b-poly(methyl methacrylate) (P3AT-b- PMMA) 之硬桿-柔曲團聯共聚高分子，並藉由分子的設計，探討聚噻吩的不同側鏈結構對其自組裝行為的影響。此外，我們同時也利用速配接合化學反應，合成出poly(3-(2-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO)雙性硬桿-柔曲團聯共聚高分子，具有n-type性質的ID4雙性小分子，以及製備P3EHT-b-PEO和ID4混合形成的錯合物，探討其自組裝行為與其光電性質。最後，為了更進一步有效地提升有機光電元件的表現，本研究也合成出新穎且不同組成的予體-受體硬桿-硬桿團聯共聚高分子poly(3-alkylthiophene)-b-poly(thiophene-alt-isoindigo) (P3AT-b-PTID)，並探討其自組裝行為與其光電性質。
一系列含不同PMMA的體積分率之P3AT-b-PMMA硬桿-柔曲團聯共聚高分子已被合成出來，其合成路徑為先分別利用Grignard metathesis (GRIM)和陰離子聚合方法聚合出P3AT和PMMA，再利用速配接合化學反應將兩段高分子P3AT和PMMA接在一起，其中P3AT為含有三種不同側鏈結構的聚噻吩，分別是含有6個碳且直鏈的poly(3-hexythiophene) (P3HT)、含有12個碳且直鏈的poly(3-dodecylthiophene) (P3DDT)、以及含有8個碳具支鏈的poly(3-(2-ethylhexyl)thiophene) (P3EHT)。將此P3AT-b-PMMA當作是一模型硬桿-柔曲團聯共聚高分子，本研究可藉由同時調控硬桿-硬桿分子間的交互作用力(rod-rod interaction)、硬桿-柔曲分子間的交互作用力(rod-coil interaction)、及兩鏈段高分子之構型的不對稱性(conformational asymmetry)，得到多樣化的結構。當聚噻吩的側鏈結構由6個碳直鏈變成12個碳直鏈，再變成8個碳支鏈，硬桿-硬桿和硬桿-柔曲彼此分子間的交互作用力隨著側鏈所佔據的空間增大而減小。因改變側鏈的結構，可調控的構型的不對稱性、硬桿-硬桿和硬桿-柔曲兩交互作用力的競爭、以及結晶的驅動力，將導致當PMMA體積分率在0.5左右時，會有多樣化的結構出現，如層狀結構(lamellae)、六方最密堆積結構(hexagonal phase)、六方堆積到gyroid結構的相變化(cylinder-to-gyroid phase transition)、以及不規則結構的相(disordered phase)。
我們同時也利用速配接合反應合成出雙性硬桿-柔曲團聯共聚高分子poly(3-(2-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO)。為了將來在光電元件的應用，降低柔曲鏈段在導電-絕緣(硬桿-柔曲)團聯共聚高分子中的含量，我們聚焦在PEO體積分率(fPEO)較小時，其自組裝的行為。當fPEO為0.18與0.30時，共聚高分子會自我組裝形成六方最密堆積及層狀結構。隨著溫度的上升，兩者都可以觀察到規則結構到另一個規則結構的相變化，分別是六方最密堆積到gyroid和層狀到gyroid等相變化。此外，我們也成功合成出具有n-type性質的ID4雙性小分子。接著，我們利用ID4小分子中的羧基和PEO中的醚基之間的氫鍵的作用力，成功地製備了P3EHT-b-PEO(ID4)x的錯合物，其中x為ID4對PEO單體的莫爾分率。隨著ID4莫爾分率的增加，這些錯合物不僅逐漸改變其形態，從層狀到gyroid，也比起原本團聯共聚高分子降低了錯合物的segregation strength。
我們成功利用Stille偶合反應(Stille coupling reaction)，合成出新穎且不同組成的予體-受體硬桿-硬桿團聯共聚高分子poly(3-alkylthiophene)-b-poly(thiophene-alt- isoindigo) (P3AT-b-PTID)，其中P3HT和P3EHT是予體鏈段，而PTID為受體鏈段。這全共軛團聯共聚高分子會自我組裝形成獨特的予體-受體結構，且具有不同的結晶結構。當P3AT-b-PTID被用在光反應層並製備成全高分子太陽能電池，則此兩團聯共聚高分子皆具有高的開路電壓(Voc)，其值皆高於0.9伏特。在效率方面，以P3HT-b-PTID製備成的元件具有最佳的表現，其PCE為0.79%，不僅高於以P3EHT-b-PTID製備成的元件，也高於以P3HT/PTID混摻所製備成的元件。
綜合上述的結果，我們可以透過改變聚噻吩的側鏈結構，增加硬桿-柔曲團聯共聚高分子之構型的不對稱性，降低聚噻吩的硬桿-硬桿分子間的交互作用力，可以得到gyroid結構。對於有機光電元件來說，此gyroid結構是理想的形態之一。此外，我們更進一步可以添加具有n-type性質的小分子於硬桿-柔曲團聯共聚高分子中，在此情形下也能得到gyroid結構，如此更有潛力應用在有機太陽能電池上。在這個研究基礎上，我們合成出新穎的予體-受體硬桿-硬桿團聯共聚高分子，透過聚噻吩側鏈結構的改變，將有機會得到gyroid結構，能更加提升有機太陽能電池的效率。

關鍵字

團聯共聚高分子 ； 硬桿-硬桿分子間的交互作用力 ； 硬桿-柔曲分子間的交互作用力 ； 構型的不對稱性 ； 予體-受體 ； 自組裝

並列摘要

Abstract
Optoelectronic devices fabricated from organic or polymeric materials have received a great deal of attention due to their significant potential as low cost, flexible and lightweight large-area devices. Controlling ordered morphology of material in 10-nm length scale is expected as one of important issues for optimizing the performance of organic devices. Using intriguing self-assembled behaviors of block copolymers (BCPs) is an emerging and promising strategy for achieving such nanomorphology. Manipulating the non-lamellar and bicontinuous nanostructures through changing volume fraction is well-developed technique for conventional coil-coil block copolymers, but it is not always effective for π-conjugated polymer-based rod-coil block copolymers. In addition, using coil-coil BCPs as photoactive layer cannot improve the performance of devices efficiently due to their insulating properties. In this dissertation, the synthesis of poly(3-alkylthiophene)-b-poly(methyl methacrylate) (P3AT-b-PMMA) rod-coil block copolymers via click chemistry are explored. The fundamental self-assembly of P3AT-b-PMMA is studied and their versatile nanostructures are observed under rational molecular design. Besides, we also synthesize amphiphilic rod-coil block copolymer via click reaction, poly(3-(2-ethyl- hexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), n-type ID4 amphiphile, and prepared the P3EHT-b-PEO(ID4)x complexes. The self-assembly and optoelectronic properties of complexes are explored. Finally, in order to further enhance the performance of devices, the novel all-conjugated donor-acceptor rod-rod block copolymers, poly(3-alkylthiophene)-b-poly(thiophene-alt-isoindigo) (P3AT-b-PTID), are designed, synthesized and characterized.
A series of well-defined P3AT-b-PMMA rod-coil block copolymers with different PMMA volume fractions (fPMMA) have been successfully synthesized via Grignard metathesis (GRIM) polymerization of P3AT and anionic polymerization of PMMA followed by click chemistry, where poly(3-hexythiophene) (P3HT), poly(3-dodecylthiophene) (P3DDT), and poly(3-(2-ethylhexyl)thiophene) (P3EHT) are used as P3AT blocks. While using P3AT-b-PMMA as a model, versatile self-assembly morphology of rod-coil copolymer can be achieved by simultaneously adjusting the rod-rod interaction, rod-coil interaction and conformational asymmetry. By altering the alkyl side chain of polythiophene from linear hexyl to longer dodecyl and to branch 2-ethyl hexyl, both rod-coil and rod-rod interaction are decreased with increasing spatial occupation of alkyl side chain which have been quantitatively determined for this type of rod-coil copolymer. With tunable conformational asymmetry, competition between rod-rod and rod-coil interactions, and crystallization-driven force, the presence of versatile morphology, i.e. lamellar, hexagonal structures, cylinder-to-gyroid phase transition and disordered phase, can be observed for long sought composition at approximately fPMMA = 0.5.
We also successfully use click chemistry to synthesize amphiphilic rod-coil block copolymer, P3EHT-b-PEO. For optoelectronics applications, lowering insulating coil segments in rod-coil block copolymers is crucial. We thus focus on the self-assembled behaviors at low PEO volume (fPEO) fractions. After thermal annealing, P3EHT-b-PEO block copolymers would self-assemble into hexagonal and lamellar structures at room temperature at fPEO = 0.18 and 0.30, respectively, and they both show gyroid morphology through order-order transition at elevated temperature. Besides, a new amphiphilic n-type acceptor, ID4, is successfully synthesized. After ID4 is blended with P3EHT-b-PEO with fPEO = 0.30, a series of P3EHT-b-PEO(ID4)x complexes have been successfully prepared through hydrogen bonding, where x is ID4 per repeating unit of PEO in molar ratio. As increasing binding fractions, the complexes not only change their morphology from lamelle to gyroid, but also shows reduced segregation strength compared to neat P3EHT-b-PEO block copolymer.
A series of fully conjugated donor-acceptor rod-rod block copolymers, P3AT-b-PTID, have been synthesized using Stille coupling reaction under microwave irradiation. While P3HT and P3EHT are used as donor block, PTID is used as acceptor block. These novel block copolymers can self-assemble into unique donor-acceptor morphology with different crystalline structures in bulk state. When P3AT-b-PTID block copolymers are used as photoactive layer to fabricate all-polymer solar cells, their Voc values are both higher than 0.9 volt. The P3HT-b-PTID device has the highest efficiency with a value of 0.79, which is better than devices fabricated with P3EHT-b-PTID and P3HT/PTID blend.
In summary, we can increase the conformational asymmetry of rod-coil block copolymer, and reduce its rod-rod interaction through introducing bulky side chain on the thiophene ring. Thus we can obtain the bicontinuous and interpenetrating gyroidal structure, which is one of ideal morphology for organic devices. We can also obtain gyroid morphology, as we further add n-type amphiphilic acceptor into rod-coil block copolymer. Based on the study of self-assembly of rod-coil block copolymer, we can synthesize novel all conjugated donor-acceptor P3AT-containing block copolymer with different side chain structure on the thiophene ring. Using this strategy, gyroid of donor-acceptor block copolymer might be achieved in the future, which could enhance the performance of organic photovoltaics more efficiency.

並列關鍵字

block copolymer ； rod-rod interaction ； rod-coil interaction ； conformational asymmetry ； donor-acceptor ； self-assembly

參考文獻

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