Synthesis And Properties Of Hexafluoroisopropylidene-containing Sulfonated Poly(arylene Ehtor&thioether Phosphine Oxide)s For Proton Exchange Membranes

Up to now, perfluorosulfonic acid PEMs such as Dupont's Nafion are the only commercially available, state-of-the art membrane used as PEM, but could not meet the requirements of large-scale commercialization of PEMFC due to their disadvantages. Therefore, alternative aromatic PEM materials with good comprehensive properties attract more and more attention. Sulfonated poly aryl (thio) ether phosphine oxide were expected to be used as the matrix of the high temperature PEM or doped PEM containing inorganic compounds due to the water retention and excellent adhesive ability of the phosphine oxide moieties. In this article, the incorporation of hexafluoroisopropylidene moieties to the resultant polymers is an attempt to increase the hydrophobicity of nonsulfonated segments, to control their nanophase separated structure, and thus to improve the comprehensive performance.In Chapter 2, 2,2-Bis(4- thiophenyl)hexafluoropropane was synthesized through"addition– elimination","Newman-Kwart rearrangement"and"Hydrolysis reaction"with2,2-Bis(4-hydroxyphenyl)hexafluoropropane as the basic raw material.Compared to poly(arylene ether)s, the study of poly(arylene thioether)s are limited .One of the most important reasons is that the dimercapto monomers are hard to be synthesized and purified due to their instability. Therefore, the synthesis of dimercapto monomers is the key of developing new poly(arylene thioether)s.In Chapter 3, the hexafluoroisopropyl hydrophobic group and poly(thioether) backbone were incorporated into sulfonated sulfonated poly(arylene thioether phosphine oxide)s by direct polycondensation in order to adjust the microphase separation structure and thus improve the properties of the resulting polymer. it is desired that the introduction of hydrophobic CF3 functional groups can improve proton transfer by facilitating the forming of hydrated ionic channels and produce distinct nanophase separation between the hydrophilicity and hydrophobicity domains so as to protect the membrane structure as water is absorbed.Compared to poly (arylene ether)s, poly(arylene thioether)s exhibited higher proton conductivity, lower water absorption, better dimensional stability. For example, sPTPOF-100 showed the water absorption of 29% and a proton conductivity of 9.1×10?2 S/cm at 80℃,which are similar to Nafion 117. However, the swelling ratio was only 5.3%, much lower than that of Nafion 117. AFM showed distinct phase-separated structures and continuous ion channels, which are beneficial to the mechanical property and proton conductivity in the same time.In Chapter 4, sulfonated hexafluoroisopropylidene-containing sulfonated poly(arylene ether phosphine oxide)s (sPEPOF) were prepared by polycondensation of sulfonated bis(4-fluorophenyl)phenyl phosphine oxide and 2-bis(2,6-difluoroph- enyl)benzimidazole with 2,2-Bis(4-hydroxyphenyl)hexafluoropropane.The perform- ance test of the sPEPOF further validates the conclusions in Chapter 3: sPTPOF exhibited excellent performance due to the introduction of poly(thioether) backbone. sPEPOF-100 exhibited a proton conductivity of 6.9×10?2 S/cm at 80℃,which are lower than the that of sPTPOF-100. However, the swelling ratio was 7.8%, higher than that of sPTPOF-100. AFM exhibited that sPTPOF have more obvious phase-separated structures but smaller size of ionic channels.sPTPOF and sPEPOF membranes hold a potential prospect in PEM applications due to their excellent overall properties.