利用點擊反應合成與鑑定磺酸化聚三唑燃料電池質子交換膜及主鏈與側鏈含氧代氮代苯併環己烷之熱交聯型聚三唑高分子

Abstract

本論文分為兩個部分，皆是利用點擊反應為工具應用於： (i) 合成磺酸化聚三唑燃料電池用質子交換膜 (ii) 合成主鏈與側鏈含氧代氮代苯併環己烷之熱交聯型聚三唑高分子

(i) 磺酸化聚三唑燃料電池質子交換膜 近年來有許多不同種類的質子交換膜應用於燃料電池中，其中非含氟的高分子材料為基材之質子交換膜最被廣泛研究。經由導入高含量之磺酸根於高分子中，非含氟材料之質子交換膜可達高的質子導電度，但此方式也同時耗損交換膜的機械性質，並引起了甲醇穿透的問題。此外這些聚集的磺酸根離子也將造成質子交換膜過度澎潤甚至溶於甲醇水溶液中。其中交聯結構的應用是有效率且簡便的方法來克服這些問題。但是交聯結構的導入通常也會導致質子導電度的犧牲。此外交聯結構往往會造成空間的內縮或是產生親疏水相(hydrophilic/hydrophobic)的不相容，因此最終造成相分離的情況產生。所以研究如何改善質子導電度且降低甲醇穿透的問題並同時不犧牲交換膜的機械性質和化學穩定性仍然具有相當大的挑戰。 第一篇研究中，我們將屬於酸性之磺酸根與點擊反應後所形成之屬於鹼性之三唑雜環官能基所產生之酸鹼作用力視為一種物理性交聯，此交聯結果能使傳導質子之離子叢集更均勻的分散並讓傳導質子之離子通道無序的分布與連續。這樣的效應可以使得導電度在沒有明顯損失的情況下讓甲醇穿透率大幅的下降。利用酸鹼作用力所產生物理性交聯之導入，與商業品Nafion 117比較，在選擇性方面有不錯的提升，意味著此方法可能有不錯的潛力應用於燃料電池質子交換膜中。 第二篇研究中，我們利用修飾上炔丙基官能基之黏土經由點擊反應以原位聚合的方式製備出脫層型態之磺化聚三唑高分子奈米複合材料。經由導入少量的黏土於磺化聚三唑高分子中，黏土層達到脫層型態且均勻的分散，因而有效改善交換膜的熱性質、機械性質、甲醇穿透、保水性、離子通道的大小和離子叢集的分散性。導入少量的黏土於磺化聚三唑高分子中展現高的選擇率，也表示此方法有潛能應用於燃料電池質子交換膜中。

(ii) 主鏈與側鏈含氧代氮代苯併環己烷之熱交聯型聚三唑高分子 交聯是一種非常有效率且便利的手法去提升高分子的熱性質與機械性質。許多研究皆在討論氧代氮代苯併環己烷(交聯劑)導入高分子後對高分子所帶來的影響。但大部分的研究皆在探討氧代氮代苯併環己烷導入的量對高分子的影響，就我們所知，尚未看到探討氧代氮代苯併環己烷導入高分子中之不同位置所產生的效應。為了研究氧代氮代苯併環己烷在高分子上不同位置所產生的效應，我們設計了兩種新穎的氧代氮代苯併環己烷單體，其雙邊皆具有炔丙基官能基之結構，接著利用點擊反應合成出兩種不同種類的高分子，分別為主鏈與側鏈上接有氧代氮代苯併環己烷之高分子。交聯後之高分子在熱性質與機械性質方面，側鏈型高分子比主鏈型高分子之性質來的要好許多。經由動力學分析後，我們認為這是來自於交聯劑位置的不同所導致交聯過程中難易度的不同，以至於最終交聯程度有所差異進而影響高分子性質。因此，我們得知若藉由交聯劑於高分子結構上不同位置之設計，相同量的交聯劑設計於高分子側鏈便能比設計於高分子主鏈上之效果來的提升更多，甚至少量之交聯劑設計於高分子側鏈便能達到所要的需求。如此一來或許能省下不少成本，其應用性更加廣泛。

There are two sections that both of them were using the click chemistry as the tool in this thesis: (i) Synthesize the sulfonated polytriazole proton exchange membrane for fuel cells (ii) Synthesize the thermally cured polytriazole polymers incorporating main or side chain benzoxazine crosslinking moieties

(i) Synthesize the sulfonated polytriazole proton exchange membrane for fuel cells Among various types of proton exchange membranes (PEMs) for fuel cells, several nonfluorinated polymeric materials are attracting more attention as alternatives to perfluorinated polymer membranes. The nonfluorinated PEMs can achieve high proton conductivities by introducing high extent of sulfonic acid groups, but tend to deteriorate the mechanical strength and permeability of PEMs simultaneously. The aggregation of conductive sites will cause these PEMs highly swollen or dissolved in aqueous/alcoholic solutions. Crosslinking appears to be an efficient and simple approach to overcome these problems, however, it usually leads to a sacrifice in proton conductivity. In addition, microphase tends separation tends to occur in such crosslinking structure due to contraction of space or incompatibility between hydrophilic (sulfonic acid groups) and hydrophobic (crosslinker) components. The development of more efficient membranes with improved proton conductivity and reduced methanol crossover without detrimentally mechanical and chemical stabilities remains an important challenge. (Part 1) Sulfonated polytriazole (SPTA) in which the acidic sulfonic acid and basic triazole groups act as physical crosslinking sites within a polymer backbone has been successfully prepared, for use as a proton exchange membrane, using the click reaction. The acid-base interactions of the SPTA membranes leads to the formation of well-dispersed ionic clusters and the random distribution of ion channels with good connectivity resulting in lower methanol permeabilities at ambient temperatures and similar or higher proton conductivities than Nafion 117 at 80 °C in conditions of near zero relative humidity. Additionally, the selectivity of SPTA is approximately four times higher than that of Nafion 117, thus it may have potential for use in direct methanol fuel cells (DMFCs). (Part 2) Sulfonated polytriazole-clay (SPTA-clay) nanocomposites are successfully prepared by in situ polymerization of SPTA using click chemistry in the presence of propargyl-functionality modified clay. The clay layers are exfoliated and well dispersed within the SPTA matrix resulting in improvements in thermal stability, mechanical strength, methanol permeatbility, water retention, ion channel size, and ionic cluster distribution. The SPTA-clay nanocomposite membranes with small amounts of clay in the SPTA matrices possess higher selectivity’s; defined as the ratio of proton conductivity to methanol permeability, and thus have potential as proton exchange membranes (PEMs) in direct methanol fuel cells (DMFCs).

(ii) Synthesize the thermally cured polytriazole polymers incorporating main or side chain benzoxazine crosslinking moieties (Part 3) Crosslinking is an efficient and simple approach to enhancing the thermal and mechanical properties of polymers. Numerous studies have reported such enhancements by the incorporation of benzoxazine (a cross-linker) in the polymer’s structures. The great majority of the studies have focused on a discussion of the benzoxazine content. As far as we know, there has been no discussion related to effects arising from the position of benzoxazine incorporation. In order to investigate any such effects, we synthesized new benzoxazine monomers (SBz and MBz), containing bis-propargyl functional groups and new main chain and side chain benzoxazine functionalized polytriazole polymers, with the above benzoxazine moieties in the repeat unit, using click chemistry. The resulting thermal and mechanical properties of Cured-PTA-SBz-10 were better than those of Cured-PTA-MBz-10, and the Cured-PTA-SBz-4 and Cured-PTA-SBz-6 were closed or even better than those of Cured-PTA-MBz-10. We assumed that this is attributable to the position effect resulting the differing degrees of polymer crosslinking. To better understand any thermal curing effects related to the positions of benzoxazine moieties in the polymer chain, we performed dynamic DSC measurements by Kissinger and Ozawa methods. Therefore, when designing the polymer, by giving consideration to the position of the cross-linker, the resulting thermal and mechanical properties can be enhanced to the extent that an equivalent polymer can be formed with a reduced amount of cross-linker leading to cost reduction.