以格林鈉反應合成全共軛雙嵌段共聚高分子PPP-P3EHT及其共結晶行為、自組裝結構與光電性質研究

Abstract

含有共軛鏈段之團聯共聚高分子，由於其擁有結晶行為與熱穩定性和自組裝行為上的特點，並擁有光電特性，在近年來越來越受到學術甚至是產業界上的注意。本論文利用格林納聚合法合成一系列的雙共軛鏈段之團聯共聚高分子 PPP-P3EHT 並控制PPP的分子量使之固定在一定鏈段，進而變動P3EHT的分子量以便於詳細的探討其自組裝與結晶行為。在以分子相似度及結晶動力學的平衡為考量上，可結晶的雙共軛鏈段之團聯共聚高分子其不相似的兩個區段產生共晶會對其相圖有極大的影響。在本論文中我們利用廣角X光繞射儀(WAXS)、小角度X光繞射儀(SAXS)、 示差掃描熱量分析儀(DSC)及穿透式電子顯微鏡(TEM)所得到的結果來探討一系列的雙共軛鏈段之團聯共聚高分子 PPP-P3EHT其多種結晶性質相互作用所導致的自組裝行為。儘管 PPP 及P3EHT 這兩個鏈段在主鏈及支鏈的結構上相差極大， PPP 及 P3EHT 這兩個鏈段還是能夠形成交互排列的共晶結構，並在支鏈相互穿插形成一個單一相。共晶結構的形成是由於 PPP 鏈段較大的結晶熱焓，使得 PPP 鏈段在結晶時能夠引入結晶速度較慢、較差的 P3EHT 鏈段，並藉此形成共晶。雙共軛鏈段之團聯共聚高分子 PPP-P3EHT之結晶結構隨著嵌段比例之不同而改變，當P3EHT比例逐漸上升時，依序能夠觀察到 PPP 結晶為主的奈米線、兩鏈段互溶的共晶結構、由共晶結構及 P3EHT 結晶所組成的層狀結構、兩鏈段微觀相分離所導致的層狀結構以及最後P3EHT結晶所產生的奈米線。值得一提的是，共晶及 P3EHT 結晶所組成的層狀結構是由自結晶與共晶所競爭、平衡而導致的結果。此實驗結果顯現出不同主鏈雙共軛鏈段之團聯共聚高分子在共晶行為上的本質，並對自組裝行為、甚至對未來的光電性質應用，提供新穎的設計與理念。

In this study, we synthesized a series of monodisperse all-conjugated BCPs of poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-(2-ethylhexyl)thiophene) (PPP-P3EHT) with different block ratios by varying P3EHT to a nealy fixed PPP molecular weight to detail their self-assembly and crystallization behavior. Gel permeation chromatographer and NMR spectra were used to characterize the block copolymers. Wherein driven by molecular affinity and balance in the crystallization kinetics, the ability to co-crystallize dissimilar yet self-crystallizable blocks of a block copolymer (BCP) into a uniform domain may strongly affect its phase diagram. In this study, we investigated this multi-crystallization effect in a series of all-conjugated poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-(2-ethylhexyl)thiophene) (PPP-P3EHT) BCPs by using a combination of wide-angle and small-angle X-ray scattering, differential scanning calorimetry, and transmission electron microscopy measurements. Despite vastly different side-chain and main-chain structures, PPP and P3EHT blocks are able to co-crystallize into a single uniform domain that comprises of alternating PPP and P3EHT main-chains with mutually interdigitated side-chains spaced in-between. The formation of the co-crystals (P+E) was driven by a large crystallization enthalpy of PPP that allows to incorporating less crystallizable P3EHT into the domain as PPP crystallizes. By varying P3EHT fraction in the copolymers, PPP-P3EHTs form hierarchical superstructures including nanofibrils with predominately PPP crystals, co-crystalline P+E nanofibrils, a bilayer lamellar structure composed of the co-crystalline P+E layer and a pure P3EHT crystalline layer, a microphase-separated bilayer lamellar structure composed of fully PPP and P3EHT crystalline domains, and finally, nanofibrils with mainly P3EHT crystals. In particular, the presence of the co-crystalline lamellar structure is the manifestation of interaction balance between self-crystallization and co-crystallization of the dissimilar polymers on the resulting nanostructure of the BCP. The current study demonstrates the co-crystallization nature of all-conjugated BCPs with different main chain moieties and may provide new guidelines for the organization of π-conjugated BCPs for future optoelectronic applications.