含側鏈共軛基團高分子之合成、形態及元件應用

Syntheses, Morphology, and Device Applications of Polymers with Pendent Conjugated Moieties

徐榮慶(Jung-Ching Hsu)

指導教授 ： 陳文章

共同指導教授 ： 平尾明(Akira Hirao)

國立臺灣大學/工學院/化學工程學研究所/博士(2011年)

https://doi.org/10.6342/NTU.2011.03379

摘要

擁有側鏈共軛基團之非主鏈共軛高分子，具有精確光電性質及絕佳的溶解度適合於元件上的應用。此類的高分子可以精確調控光電特性的且建立結構和性質的關係，此外，此類高分子的形態和主鏈共軛高分子極為不同。本論文設計並製備出新穎高分子帶有側鏈芴(fluorene)及三苯胺(triphenylamine)共軛基團，並對其合成、形態、光電特性與元件應用進行深入的研究。探討其高分子構形及奈米複合材料於記憶體元件上的應用。這些研究主題將於下段開始再進一步描述。

本文的第一個部分(第二章)-由陰離子聚合苯乙烯末端取代不同重複單元芴共軛基團-合成在苯乙稀末端位置，接上不同重複單元(n=1, n=2及n=3)芴(fluorene)共軛基團之單體(St-Fl, St-Fl2, St-Fl3)，藉由活性陰離子聚合成高分子。其中St-Fl, St-Fl2單體可以精準得到預期的分子量，高分子分子量分佈 (PDI) 為1.08以下，且陰離子聚合行為和苯乙烯類似，St-Fl3單體的陰離子聚合行為則需要再進一步分析。同時本研究也會探討單聚物在不同溶劑下的溶解性、黏度、熱性質以及光電性質。此種側鏈型高分子其光物理特性與芴寡聚物類似，隨著芴的數目增加吸收及放光光譜的尖峰位置隨著紅移。此研究結果顯示陰離子聚合可用於聚合帶有側鏈芴共軛高分子的單體，且得到精確的物理特性。

本文的第二個部分(第三章)-以超分子方式使用在具有側鏈芴共軛基團嵌段共聚高分子(P(St-Fl)-b-P2VP)及PCBM複合膜於非揮發性記憶體元件應用-具有側鏈芴共軛基團之嵌段共聚高分子(Poly(fluorenylstyrene)-block-poly(2-vinylpyridine) (P(St-Fl)-b-P2VP))為利用陰離子聚合得到。由吸收及發光光譜圖譜結果顯示此兩高分子鏈段P(St-Fl)和P2VP，分別會和PCBM產生電荷轉移複合物(charge transfer complex)，且P2VP可以藉由此作用力分散PCBM的大小，進而影響記憶體元件的表現。P(St-Fl)-b-P2VP和PCBM混摻後，成功應用在一次寫入與多次讀取(WORM)記憶體元件，且PCBM混摻的量會影響到臨限電壓 (threshold voltage)及電流開關比(ON/OFF ratio)。在低導電態，電子注入的機制為熱離子發射(thermionic emission)，從低導電態轉變為高導電態轉變的機制可以用電場引導電荷轉移解釋。此研究結果提供一嶄新的方向，以超分子方式調控記憶體元件表現。

本文的第三個部分(第四章)-合成並探討具有側鏈芴(fluorene)共軛基團之非對稱星狀高分子(P(St-Fl)-b-P2VP)其形態及元件應用。非對稱星狀高分子為一含側鏈芴(fluorene)共軛基團(P(St-Fl))的支臂分別含有2及4支臂數的P2VP (AB2及AB4)，利用陰離子聚合得到且高分子分子量分佈 (PDI) 為1.11以下。藉由SAXS， WAXS 及 TEM觀察，層狀堆疊排列(lamellar)及六角穿孔層板( hexagonally perforated lamellae)形態隨P2VP支臂數目不同而有改變。添加 [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) 會提昇P(St-Fl)的排列。由吸收及發光光譜圖譜結果顯示側鏈芴共軛基團和2-pinylpyridine，分別會和PCBM產生電荷轉移複合物(charge transfer complex)。AB2和PCBM混摻後，成功應用在一次寫入與多次讀取(WORM)記憶體元件，且PCBM混摻的量會影響到臨限電壓 (threshold voltage)及電流開關比(ON/OFF ratio)。在低導電態，電子注入的機制為熱離子發射(thermionic emission)，從低導電態轉變為高導電態轉變的機制可以用電場引導電荷轉移解釋。此研究結果提供一嶄新的方向，製備具有donor-acceptor的非對稱星狀高分子應用在記憶體元件表現。

本文的第四個部分(第五章)-合成新穎具有側鏈芴共軛基團星狀高分子及製備多光色規則孔洞薄膜-藉由陰離子聚合得到不同支臂數目3,4,及8個具有側鏈芴(fluorene)共軛基團星狀高分子，對其合成、光物理性質及形態進行探討。其中，僅有8個支臂數目的星狀高分子因擁有較高分子量，能夠藉由滴鍍(drop-casting)方式形成規則孔洞薄膜，孔洞的大小受到溶液的濃度及外界濕度影響。形成的孔洞薄膜其吸收及放光光譜皆比原本吸收及放光光譜紅移，且由於芴共軛基團具有發藍光的性質，可以得到均勻發藍光的孔洞薄膜。更進一步的，藉由適當的選擇材料poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-(2,1′,3)-thiadiazole) 或 bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2(acac))，混摻1%的量即可產生能量轉移得到發綠光或紅光的孔洞薄膜。此研究結果提供一嶄新的方向，可藉由合成帶有側鏈芴共軛基團支臂的星狀高分子，得到不同光色的規則孔洞薄膜。

本文的第五個部分(第六章)-藉由基團轉移聚合法合成線性及星狀具有側鏈三苯胺共軛基團高分子於記憶體元件應用-三苯胺結構(TPA)具有好的電洞傳導性質。藉由基團轉移聚合法(Group transfer polymerization)合成線性(PTPMA)及星狀 (N(PTPMA)3)具有側鏈三苯胺共軛基團高分子，星狀高分子為利用新穎擁有3個起始官能基的核心當作起始劑。PTPMA 及N(PTPMA)3成功應用在動態隨機存取(DRAM)揮發性記憶體元件，加入PCBM混摻後，元件轉換為一次寫入與多次讀取(WORM)非揮發性記憶體性質或導體(conductor)性質。一次寫入與多次讀取非揮發性記憶體，在高導電態或是低導電態皆可以維持104秒，顯示有好的穩定性。吸收及放光光譜顯示三苯胺結構和PCBM之間會產生電荷轉移複合物，進而影響PCBM大小。電荷捕捉/散逸效應（trapping-detraping）及電場引導電荷轉移(field-induced charge transfer)分別為動態隨機存取記憶體元件及一次寫入與多次讀取記憶體的機制。星狀高分子的立體障礙影響電子傳遞到PCBM的LUMO效率，進而影響到臨限電壓 (threshold voltage)及電子傳導機制。此研究結果顯示添加不同比例的PCBM或高分子構形會影響記憶體元件的性質。

關鍵字

陰離子聚合 ； 形態 ； 高分子記憶體

並列摘要

Non-conjugated backbone polymers with pendant π-conjugated moieties could have precisely optoelectronic properties and excellent solubility for device applications. Such polymers have precisely defined electronic/optoelectronic properties and can be used to establish the structure-property relationship. Besides, the morphology of such polymers may lead to significant difference on the electronic/optoelectronic properties from the main chain conjugated polymers. In this thesis, we explore the synthesis, morphology, and optoelectronic device applications of new polymers with pendent conjugated moieties, including oligofluorene and triphenylamine. The effects of polymer architectures and nanocomposites on memory devices are reported. The following summarize the important discovery of this thesis.

1. Living Anionic Polymerization of Styrene Derivatives para-Substituted with π-Conjugated Oligo(fluorene) Moieties (chapter 2): the anionic polymerization of styrene monomers para-substituted with π-conjugated mono-, di-, and tri(9,9-dihexylfluorene) moieties, St-Fl, St-Fl2, and St-Fl3, was examined. The anionic polymerization of St-Fl3 was also indicative to proceed in a living manner but with an unpredictable molecular weight. Both AB and BA diblock copolymers with the well-defined and expected structures could be successfully prepared by the sequential addition of St-Fl or St-Fl2 followed by styrene and vice-versa. The optical absorption and luminescence spectra of the studied polymer films showed well-resolved vibronic structures and the peak maxima was progressively increased as the fluorene chain length increased. The luminescence spectra also showed reduced aggregation/excimer emission in comparison with that of parent polyfluorene.

2. A Supramolecular Approach on using Poly(fluorenylstyrene)-block -poly(2-vinylpyridine):PCBM Composite Thin Films for Non-Volatile Memory Device Applications (chapter 3): supramolecular composite thin films of poly[4-(9,9-dihexylfloren-2-yl)styrene]-block-poly(2-vinylpyridine) (P(St-Fl)-b-P2VP):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were prepared for write-once-read-many times (WORM) non-volatile memory devices. The optical absorption and photoluminescence results indicated the formation of charge transfer complexation between the P2VP block and PCBM, which led to the varied PCBM aggregated size and memory characteristics. The ITO/PCBM:(P(St-Fl)-b-P2VP)/Al device exhibited the WORM characteristic with low threshold voltage (-1.6 to -3.2 V) and high ON/OFF ratio (103 to 105) by tuning the PCBM content. The switching behavior can be explained by the charge injection dominated thermionic emission in the OFF state and field-induced charge transfer in the ON state.

3. Synthesis and Morphology of New Asymmetric Star Polymers of Poly[4-(9,9-dihexylfloren-2-yl)styrene]-block-Poly(2-vinylpyridine) and Their Non-Volatile Memory Device Applications (chapter 4): New 3-arm AB2 and 5-arm AB4 asymmetric amphiphilic star polymers of poly[4-(9,9-dihexylfloren-2-yl)styrene] (P(St-Fl))-block-poly(2-vinylpyridine) (P2VP) with narrow molecular weight distributions (Mw/Mn < 1.11) were synthesized. The synthesis methodology was based on living anionic polymerization using 1,1-diphenylethylene (DPE)-functionalized P(St-Fl) with two or four benzyl bromide moieties followed by linking reaction with a living anionic P2VP. Depending on the arm numbers of P2VP, lamellar and hexagonally perforated lamellae morphologies were observed from the results of SAXS, WAXS, and TEM. The PCBM incorporated in the polymer matrix increased the order degree of the liquid-crystal-like morphology in the P(St-Fl) block. The new asymmetric star polymers could be blended with PCBM for electrical WORM memory devices application. The optical absorption and photoluminescence results indicated the formation of charge transfer complexation between PCBM and the 2-vinylpyridine or pendent fluorene chromophores. The switching behavior can be further explained by the charge injection dominated thermionic emission in the OFF state and field-induced charge transfer in the ON state.

4. Synthesis of New Star-Shaped Polymers with Styrene−Fluorene Conjugated Moieties and Their Multicolor Luminescent Ordered Microporous Films (chapter 5): Three polymers with different number of arms (P(St-Fl)n, n = 3, 4, and 8) were obtained by living anionic polymerization, and they exhibited a narrow molecular weight distribution (Mn/Mw <1.06). The effects of arm numbers, humidity, and solution concentration on the formation of the microporous structures were studied. It was found that the high molecular weight P(St-Fl)8 could form a highly ordered microporous film via drop-casting, but not on the polymers with the other two arm numbers. In addition, the pore diameter was reduced while enhancing solution concentration or decreasing humidity. Relatively uniform blue-emitting characteristics were obtained on the P(St-Fl)8 microporous films. Such highly ordered structure led to a red shift in photophysical properties, such as absorption and photoluminescence. Furthermore, green- and red-emission microporous films were obtained via blending a relatively small amount (~1%) of poly((9,9-dioctylfluorenyl-2,7-diyl) -co-(1,4-benzo-(2,1′,3)-thiadiazole) or bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2(acac)) through efficient energy transfer.

5. Synthesis of Linear and Star-shaped Poly[4-(diphenylamino)benzyl methacrylate] by Organocatalyzed Group transfer polymerization and Their Electrical Memory Device Applications (chapter 6): Hole-transporting triphenylamine (TPA) based polymers, the linear poly[4-(diphenylamino)benzyl methacrylate] (PTPMA) and the three-armed star-shaped poly[4-(diphenylamino)benzyl methacrylate] (N(PTPMA)3) have been synthesized by organocatalyzed group transfer polymerization (GTP). For the synthesis of N(PTPMA)3, the core-first approach coupled with the GTP was adopted using a newly-designed silyl ketene acetal initiator with three initiating points. The new hole-transporting TPA based polymers could be blended with electron-accepting PCBM for electrical memory device applications. The experimental results showed that pristine PTPMA and N(PTPMA)3 exhibited DRAM volatile electrical behavior but their PCBM composite based devices changed to the WORM non-volatile memory characteristic or conductor behavior. The optical absorption and photoluminescence results indicated that the charge transfer complexation between the TPA and PCBM led to the varied PCBM aggregated size and memory characteristics. The trapping-detraping and field-induced charge transfer effect was used to explain the different memory characteristics. The steric hindrance of the star-shaped N(PTPMA)3 compared to PTPMA probably reduced the electron transport efficiency from Al to the LUMO of PCBM in the polymer/PCBM composite based devices, such as turn-on voltage and conduction mechanism.

The thesis reveals the strategy on the synthesis of non-conjugated polymers containing pendent conjugated moieties and the importance of polymer architecture or donor/acceptor composition on tuning the device characteristics.

並列關鍵字

anionic polymerization ； morphology ； polymeric memory

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