團聯共聚高分子電解質之合成與其在燃料電池離子傳導膜之應用

Abstract

團聯共聚高分子在其一鏈段上帶有正或負離子基團稱為高分子團聯共聚電解質，由於團聯共聚高分子良好的微相分離特性可以幫助我們在薄膜中建構連續規整排列的離子傳導通道，在燃料電池的薄膜組件中運用這種材料可以有效地幫助陰陽離子的傳遞以及降低甲醇燃料的滲透。在這論文當中，我設計及合成出一些帶有側垂磺酸基以及四級銨鹽的團聯共聚高分子電解質，並製備相對應的質子傳導膜與陰離子傳導膜，高分子性質的結構鑑定與薄膜微結構於傳導性質的影響也在這本論文當中系統化地整理與討論。 在第二章節中，我合成並且鑑定一系列新穎的含側垂磺酸基團聯共聚高分子(poly(styrene-block- sulfonated hydroxystyrene) (PS-b-sPHS))，在團聯共聚高分子微相分離與離子基庫倫力的交互平衡作用下，我觀察到了一些特殊的微結構，如中空管柱、平行串珠的結構是在一般的團聯高分子中不常見的，在這些相分離結構以及側垂磺酸基的幫助下，可以有效的幫助質子的傳遞與甲醇燃料的滲透，甚至於可量得比Nafion® 117高五個次方的薄膜選擇性的離子傳導膜。 接著在第三章節中，我在含側垂磺酸基團聯共聚高分子電解質的疏水端接上兩種不同的側鏈液晶分子，發現在接枝後會改變薄膜的結晶度跟薄膜微結構的排列，並且顯著地影響質子的傳遞性質，在接了長碳鏈尾巴–C6側鏈基的高分子電解質薄膜顯示出高結晶性，相反地，接上了-CN側鏈基的薄膜經由-CN mesogenic基團的排列幫助呈現出完美的平行直線排列的結構，直線排列的範圍甚至可以到達15個微米以上，藉由這樣的排列可以有效地幫助離子的傳遞以致與–C6製成的高結晶度薄膜來比，傳導度可以提升兩倍。 最後在第四章節中，我使用了好控制與無毒性的合成法來製備了一系列帶有側垂四級銨鹽基的陰離子交換膜PS-b-PIN，這種合成方法具有環境親合的優點更容易控制陰離子基團的比例更避免掉原本有毒的chloromethylation法來接上四級銨鹽，微相分離的結構與離子傳導的關係也經系統化的驗證，顯示製得的陰離子交換膜具有連續性陰離子傳導通道以及較低的甲醇滲透，並且使用此方法製得的薄膜對比於一般常見的苯甲基位四級銨鹽離子基的薄膜，在長時間的測試下具有更穩定的鹼性穩定度。

Block polyelectrolytes are block copolymers containing one of the building segments bearing electrolyte groups. Because microphase separation could facilitate microstructure formations into well-defined polyelectrolyte domains to produce continuous ion conducting channels, the use of block polyelectrolytes for the ion conducting membranes in fuel cell applications has been demonstrated to effectively promote the ion conductivity and suppress the methanol permeability. In this dissertation, block polyelectrolytes bearing pendant sulfonic acids or quaternary ammonium groups are designed and synthesized to prepare the corresponding proton exchange membranes (PEM) or anion exchange membranes (AEM). The interplays between the polymer architecture, the morphology of the membrane and the transport properties are systematically investigated. In chapter 2, a series of novel block polyelectrolytes, poly (styrene-block- sulfonated hydroxystyrene) (PS-b-sPHS), containing pendant sulfonic acid groups attached to the backbone via propyl spacers in the sPHS domain were synthesized and characterized. Some unique morphologies, such as hallow channels and lamellar arrangement of strings of beads, were observed as a consequence of equilibrium between microphase separation and coulomb interactions between polyelectrolytes were observed. The combination of microphase separation of block polyelectrolytes and freedom of movement of pendent alkylsulfonic acids was demonstrated to effectively enhance the proton transport and suppress the methanol crossover for the PEMs, leading to the selectivity higher than Nafion® 117 by 5 times at most. In chapter 3, two different side mesogenic moieties were delicatedly incorporated in the hydrophobic segment to change the crystallinity of the hydrophobic domains, which were found to significantly affect the microstructure in nanoscale and microscale and thus to alter the transport properties. The block polyelectrolytes with the long-tailed –C6 side groups exhibit highly crysallinity. In contrast, the block polyelectrolytes with the help of -CN side groups alignment, parallel patterning of nanostructures is fabricated with excellent well-organized microphase separation at microscale (> 15 μm). For this ion conducting membrane enhances the ion conductivity higher than that membrane preparing from –C6 groups by 2 times. In chapter 4, anion exchange membranes were prepared from quaternized block copolymers PS-b-PIN, composed of a hydrophobic polystyrene segment and a quaternized polyisoprene segment bearing pendant quaternary ammonium groups. A new approach is developed to prepare the AEMs without the use of ill-defined and toxic chloromethylation to introduce quaternary ammomium groups. The resulting AEMs exhibit microphase separated morphologies, primarily determined by the compositions of PS-b-PIN. The morphology-transport properties interplays are systematically investigated, showing the interconnectivity of the hydroxide conducting domains is critical to hydroxide conduction but less important for methanol permeation. Through this method, benzylmethylammonium groups, usually seen in the widely studied quaternized polysulfones, are absent to enable the resulting AEMs exhibit high alkaline stability in strong basic environment for long term.