聚3-己基噻吩與聚異戊二烯的雙嵌段共聚高分子薄膜拉伸效應之研究：微結構和電性質

Stretching Effect on Poly(3-hexylthiophene)-block-Polyisoprene Thin Films: Microstructures and Electronic Properties

羅傑文(Jie-Wen Luo)

指導教授 ： 趙基揚

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202004058

摘要

我們利用GRIM的方法聚合出側鏈具有高度立體規則性(regioregular)的Poly(3-hexylthiophene) (rr-P3HT)，再將P3HT之末端基Br置換為醛基(P3HT-CHO)後與Polyisoprene (PI)陰離子進行耦合，合成出一系列具有不同數量之PI重複單元的雙嵌段共聚高分子(P3HT-block-PI)。我們將陰離子聚合溫度設定為-78℃，合成出主要為1,2/3,4加成的PI。1,2/3,4-PI具有略低於室溫的Tg，約為5~20℃，在室溫下為可撓式電子元件提供了可撓性，而相對於Tg遠低於室溫的高分子，如1,4-PI，具有較硬的分子鏈，因此也提升了微結構的穩定性。同時其側鏈的雙鍵具備了交聯的可能性，可以進一步提升可撓式電子元件的耐用程度，使元件具有承受反覆形變的能力。
　　在這篇研究中，我們固定P3HT的分子量並改變PI的長度，合成了三種具有不同重複單元比例的P3HT-b-PI，分別為P1、P2和P3，其中P3HT和PI重複單元的比例分別為2:1、1:1和1:2。利用小角度X光散射和差熱分析儀，我們研究了三種P3HT-b-PI的自組裝特性，由差熱分析曲線可以觀察到，P1的結晶溫度和結晶放熱量都有明顯的減少，說明P1的結晶行為可能受到了抑制，然而具有更長PI鏈段的P2和P3卻沒有在相對應的物理量上有顯著的變化。另外從P3HT-b-PI的紫外光/可見光吸收光譜中發現P1位於600nm的吸收峰值明顯較弱，說明少量1,2/3,4-PI的存在會大幅削弱P3HT的π-π堆疊程度。有別於大多數含有P3HT的rod-coil嵌段共聚高分子，在P3HT-b-PI的系統中我們發現隨著1,2/3,4-PI長度的增加，其對於P3HT結晶行為的負面影響似乎被降低了。
　　接著我們將P3HT-b-PI利用旋轉塗佈法製成薄膜，再利用光學顯微鏡、原子力顯微鏡和廣角X光散射研究薄膜在不同拉伸程度下的拉伸強度、微結構與結晶行為。從光學顯微鏡的影像中我們發現P3HT-b-PI相較於純P3HT，其拉伸狀態下的薄膜表面明顯具有較高完整性。而由於雙嵌段共聚高分子造成的微相分離，我們能從原子力顯微鏡的影像中觀察到薄膜表面具有蜂巢狀和纖維狀的微結構。有趣的是，我們也觀察到P1和P2薄膜在拉伸狀態下產生了具有方向性且有序的微結構，但並沒有看到拉伸對於P3的薄膜微結構有顯著的效應。而關於薄膜的拉伸與P3HT結晶的關係，我們發現拉伸會以多種不同且複雜的方式影響薄膜中P3HT的結晶行為，這取決於P3HT-b-PI的組成比例。

關鍵字

聚3-己基噻吩 ； 聚異戊二烯 ； 雙嵌段共聚高分子 ； 微相分離 ； 可撓式有機薄膜電晶體

並列摘要

Poly(3-hexylthiophene)-block-polyisoprene (P3HT-b-PI) diblock copolymers (BCPs) with different compositions are synthesized via effective coupling reaction between aldehyde end-functionalized P3HT (P3HT-CHO) and living polyisoprene (PI) anions. P3HT-CHO is obtained from formylation of regioregular P3HT, which is synthesized from Grignard metathesis polymerization (GRIM) of 2,5-dibromo-3-hexylthiophene. Living polyisoprene anions are obtained from anionic polymerization at -78℃, in which the PI anions are mainly in 1,2/3,4-addition with the double bonds as the side groups. As for the application of stretchable electronic devices, 1,2/3,4 addition polyisoprene has a Tg around 5~20℃, which should provide not only flexibility and stretchability of the resulting thin film at room temperature, but also the stability of the microstructure of the thin film. Furthermore, the pendant double bonds could offer the possibility of post-curing to enhance the durability of the device after repeated deformation.
　　In this thesis, we synthesize three P3HT-b-PI block copolymers having P3HT in fixed length and varied PI segments, denoted as P1, P2 and P3. The ratio of the repeating units of P3HT to PI in P1, P2 and P3 are 2:1, 1:1 and 1:2 respectively. The intrinsic self-assembly behaviors of P1-P3 are investigated by small angle X-ray scattering and differential scanning of the annealed bulk samples. A large drop of Tc and a much lower enthalpy change of crystallization are observed during the cooling process in the DSC curve of P1, indicating a suppression in crystallinity might be taken place. However, there are no obvious changes in the corresponding physical properties of P2 and P3 according to their DSC curves, even though the PI content are doubled in P2 and quadrupled in P3 comparing to P1. UV-vis spectrum of spin-coated thin films show weakened absorption at 600nm for P1, indicating significant deterioration of π-π stacking of P3HT in P1. Nevertheless, increasing the length of PI would mitigate the negative influence of PI on the crystallization of P3HT in P2 and P3, which is very different from most P3HT rod-coil block copolymer systems.
　　The stretchability, the microstructures and the crystallinity of the P3HT-b-PI spin coated thin films under various degree of strain are also investigated via optical microscopy, atomic force microscopy and grazing-incidence wide angle X-ray scattering. P3HT-b-PI thin films are found to be more intact comparing to the pristine P3HT thin film upon stretching. Cylindrical and fibrillar morphologies are observed in P1, P2, and P3 thin films. Interestingly, anisotropic ordering in microstructure induced by stretching is found in stretched P1 and P2 thin films. However, no obvious stretching effect on microstructure could be detected in P3 thin films. The effect of stretching on P3HT crystallinity in the thin films are in a complicated fashion, depending on the composition of the P3HT-PI block copolymers.

並列關鍵字

Poly(3-hexylthiophene) ； Polyisoprene ； Block copolymer ； Microphase separation ； Stretchable organic thin film transistor

參考文獻

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