硬桿-柔曲與硬桿-硬桿共軛雙區段共聚高分子自組裝行為之探討及在奈米混成系統之應用

近年來, 含有共軛鏈段之團聯共聚高分子由於本身具備的自組裝特性可進而有效藉由結構上的改變來調控其機械與光電特性，因而逐漸受到各界廣泛的注意。因此，瞭解此類含有共軛鏈段之團聯共聚高分子其自組裝特性以利後續的應用發展乃是相當重要的一環。然而目前在此研究課題上仍有許多未知的現象有待探索。本研究利用數種不同的具共軛鏈段之團聯共聚高分子來探討其自組裝行為，我們相信由本研究中所的到的實驗結果將有利於此類特殊高分子做更進一步之應發展。在本論文的第二節中提到一系列的P3HT-P2VP共軛團聯共聚高分子已被成功的合成出來並且其完整的自組裝行為包含有序-有序相轉換 (order-order transition)，有序-無序相轉換 (order-disorder transition) 和液晶 (liquid crystalline) 行為也隨即利用不同的實驗包含穿透式電子顯微鏡 (TEM)，小角X光散射 (SAXS)，廣角X光散射 (WAXS) 與吸收光譜 (UV-Vis) 等進行觀測。我們觀察到隨著P3HT在此共軛團聯共聚高分子之體積分率的不同則會產生不同的自組裝奈米結構。同時，在不同的奈米結構下，P3HT分子鏈的構形可為一硬桿直鏈 (rigid rod)，或是較為柔曲之捲曲型態 (flexible chain)，或是介於兩者之間之半硬桿型態 (semirigid chain)。由本實驗結果發現了P3HT鏈段其兼具柔曲與剛硬的特質，其分子鏈的硬度與構形會隨者共軛團聯共聚高分子自組裝過程中不同之熱力學因素影響而有所不同。在本論文的第三節中，我們提到了體積分率對稱的P3HT-P2VP共軛團聯共聚高分子具有特殊的結晶結構與相轉換特性。不同於P3HT均聚合物經溶劑揮發後之塊材中同時含有form I 及 form II 兩種 P3HT晶形，經溶劑揮發過之體積分率對稱P3HT-P2VP共軛團聯共聚高分子其塊材中僅具有單一form II 之晶形。再由TEM觀察可發現此種form II晶形是被侷限在纖維狀之自組裝奈米結構之中。我們認為此種單一form II晶形之產生是由於溶劑揮發過程中，纖維狀自組裝結構之生成對P3HT鏈段結晶之空間侷限影響。當此具form II晶形之團聯共聚高分子被加熱到~110°C ，在奈米纖維結構中之form II晶形會轉換成form I晶形。再把此一樣品進一步加熱至120°C 以上，則P3HT結晶逐漸融化而此團聯共聚高分子之自組裝結構也會由纖維狀轉變為層狀結構。在此一系列之晶形轉換與奈米結構之相變化過程可讓我們進一步的瞭解熱力學與動力學因素對P3HT-P2VP共軛團聯共聚高分子自組裝行為之影響。在本論文的第四節中提到利用格林納聚合法一系列的PPP-P3HT雙共軛團聯共聚高分子已被成功的合成出來。我們利用這一系列固定PPP鏈段分子量改變P3HT鏈段長度之具有不同體積分率的PPP-P3HT雙共軛團聯共聚高分子進行此一系統之自組裝行為探討。經由穿透式電子顯微鏡和X光散射等實驗的觀測，我們觀察到此一雙共軛團聯共聚高分子所產生的自組裝行為有別於一般的柔曲-柔曲 (coil-coil) 或是硬桿-柔曲 (rod-coil) 團聯共聚高分子。總結來說，在本論文中我們完整的觀察了含有共軛鏈段P3HT之團聯共聚高分子其自組裝行為與相轉換的特性，相較於其他剛硬之共軛高分子，如PPV，聚噻吩之衍生聚合物(poly (thiophene) derivatives) 其主鏈間C-C鍵具有足夠能力可以旋轉，因此此類團聯共聚高分子其相圖所顯示的特性有別於傳統的硬桿-柔曲團聯共聚高分子系統。隨即我們更進一步的觀察了具有P3HT鏈段之雙共軛PPP-P3HT團聯共聚高分子其自組裝特性。由於P3HT與PPP鏈段皆具有較為剛硬之分子鏈構形，因此最後此系統產生的自組裝結構為不具曲度之層狀奈米結構。此外我們亦利用PPH-PVP雙親性共軛團聯共聚高分子進行硫化鎘(CdS)半導體奈米微粒製備。一開始我們以陰離子聚合方法合成PPH-PVP之前驅物PCHD-PVP，然後經由脫氫反應得到PPH-PVP。再來分別將PCHD-PVP與PPH-PVP兩種團聯共聚高分子用來製備CdS半導體奈米微粒。經由實驗結果的觀察我們發現CdS奈米微粒被包覆在PPH-PVP微胞結構的外層，與脫氫前之前驅物PCHD-PVP與CdS所形成之微胞結構有極大的不同，此區別是由於PCHD與PPH各別在溶劑中溶解度之差異所造成。而我們亦注意到PPH-PVP團聯共聚合物吸附CdS奈米微粒之後對於發光有一quench效果，主因是由於PPH分子受到光激發後電子與電洞經由PPH-PVP/ CdS混成系統的能階傳導造成之電荷分離效應所致。

關鍵字

團聯共聚高分子； P3HT-P2VP ； P3HT晶形； PPP-P3HT ；硫化鎘(CdS)奈米微粒； PPH-PVP ； quench 效應

並列摘要

Recently, there has been a growing interest in the synthesis of block copolymers containing conjugated polymers since it may offer a new strategy for the organization of the π-conjugated polymers and the synergistic improvements of their mechanical, optoelectronic and other properties. However, understanding the self-assembly behavior of these conjugated block copolymers and controlling their molecular and structural parameters that dictate the formation of ordered microstructures for further applications is still largely unknown. In this thesis, new experimental efforts were performed to investigate the self-assembly behavior of the π-conjugated block copolymers. The outcome of this study show promises for practical uses of π-conjugated block copolymers since the resulting phase diagram offers a level of structural control that is important for future applications. In chapter 2 of this thesis, a series of π-conjugated block copolymers of regioregular poly (3-hexyl thiophene)-b-poly (2-vinyl pyridine) (P3HT-P2VP) was synthesized and their self-assembly behavior and detailed thermodynamic phase diagram including the order-order, order-disorder and the liquid crystalline transformations were investigated. It was found that the conjugated P3HT in their various self-assembled nanodomains could be of a rigid rod, or a semirigid chain, or even a fully flexible chain depending on their volume fraction of the copolymers. The observed microstructures and phase transformations reveal the importance of the semirigid nature of conjugated P3HT chains with rigidity which can be varied by the balance between various energies including the rod-rod interaction, the stretching and twisting of rod and coil blocks, and the energy associated with the interfacial curvature of the microstructure. In chapter 3 of this thesis, a unique crystallographic phase transformation of P3HT chains in the nanostructure of self-assembled P3HT-P2VP block copolymers was reported. We demonstrated that while a solvent-cast P3HT homopolymer shows a polymorphic behavior with the formation of both form I and form II crystal structures in the nanowire nanodomain, for a solvent-cast symmetrical P3HT-P2VP sample only a form II crystal structure was observed in its block copolymer nanowire nanodomain. The formation of only form II crystals of P3HT in the nanowires is believed to the related the nanoscale spatial confinement effect on the crystal growth as well as the effect of microphase separation of P3HT-P2VP system. Upon heating to temperature of ~110°C a crystallographic phase transformation from Form II crystals to Form I crystals was observed while maintaining the self-assembled nanowire structure. Notably, when heated above 120°C, the solvent-cast P3HT-P2VP nanowire undergoes a phase transition to form a lamellar nanostructure. As a result, the morphological and structural transformations of P3HT-P2VP block copolymer allow a detailed understanding of the dependence of self-assembly of P3HT based block copolymers on both kinetic and thermodynamic effects. In chapter 4 of this thesis, the self-assembly behavior of all-conjugated poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene) (PPP-P3HT) block copolymers synthesized via a sequential Grignard metathesis method (GRIM) was investigated. Subsequently, the self-assembly behavior of PPP-P3HT block copolymer system was studied to produce an experimental phase diagram showing features that differ from the phase diagram of either conventional coil-coil or fully rigid rod-coil block copolymers. To conclude, in this thesis I have investigated the self-assembly behavior and phase transformation of rod-coil block copolymers with the π-conjugated P3HT segments. In contrast to the assumed rigid-rod polymers such as PPV, poly (thiophene) derivatives (PT) have sufficient high degrees of freedom that allow for a twist motion of the carbon-carbon single bond between the adjacent thiophene rings. Therefore, the resulting phase diagram derived from the P3HT based rod-coil block copolymer system shows different features in contrast to those of the conventional rod-coil block copolymers. Subsequently, an all conjugated rod-rod block copolymer system with the π-conjugated P3HT and PPP segments were studied in this thesis. Based on the rigid-rod structure of such rod-like building blocks with their dramatically reduced coiling ability and the high persistence length, generally a low curvature of the aggregates formed during their self-assembly will result. Additionally, I synthesized organic/inorganic hybrid containing cadmium sulfide (CdS) nanoparticles using novel amphiphilic polyphenylene-b-poly (2-vinyl pyridine) (PPH-PVP) conducting block copolymer as a structure directing template in order to study the applications of π-conjugated rod-coil block copolymers on nanohybrid synthesis. PPH-PVP/ CdS in THF exhibits a new concentric ring-like structure of uniform size (~50nm) with PPH in the inner rim and PVP complexed with cadmium sulfide as the outer one due to the effects of strong intermolecular forces between PPH segments and solvophobic interactions. In particular, we found that there is an efficient energy transfer between the conducting PPH domain and CdS nanoparticle in the hybrid, resulting in an enhanced PL quenching effect.

並列關鍵字

block copolymers ； P3HT-P2VP ； P3HT crystal ； PPP-P3HT ； CdS nanoparticles ； PPH-PVP ； photoluminescence quench effect

參考文獻

72. Zhao, H.; Douglas, E. P.; Harrison, B. S.; Schanze, K. S. Langmuir 2001, 17, 8428-

52. Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. Nat.

39. Cho, G.; Jung, M.; Yang, H.; Song, J. H.; Sung, M. M. Langmuir 2006, 22, 4896-4898.

1. Bates, F. S. Science 1991, 251, 898.

2. Bates, F. S.; Fredrickson, G. H. Ann. Rev. Phys. Chem. 1990, 41, 525.

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硬桿-柔曲與硬桿-硬桿共軛雙區段共聚高分子自組裝行為之探討及在奈米混成系統之應用

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