Poly(p-terphenyl piperidinium) as anion exchange membranes. Synthesis and evaluation of properties

Sammanfattning: Alkaline exchange membrane fuel cells (AEMFC) is an interesting and attractive alternative to proton exchange membrane fuel cells (PEMFC) due to the potential use of non-precious catalysts which can reduce the overall cost of the fuel cell. An important component of the AEMFC is the anion conducting membrane. This membrane needs to possess several important properties such as a high hydroxide conductivity and sufficient stability at elevated temperatures for a prolonged time. The membrane material is a polymer which structure affects the properties. Extensive research has been made in the last decade in order to find a material that posses all the required properties. In this work, polymers with an all-carbon based backbone and incorporated piperidinium ions, poly(p-terphenyl piperidnium), are synthesized and studied with regards to the structure of the piperidinium ion. Two different polymers were synthesized via superacid catalyzed polycondensations of p-terphenyl, with either 4-piperidone or N -methyl-4-piperidone. These polymers were then functionalized via Menshutkin reactions with alkyl and benzylic halides of different sizes and structures. Seven polymers were successfully synthesized. Three more were attempted, but unsuccessful due to sterical restrictions in the functionalization step, e.g. a limit with regard to the size of the alkylhalide used. Three of the successfully synthesized polymers poly(p-terphenyl N -methyl-N -isobutyl-piperidinium), poly(pterphenyl N -methyl-N -cyclohexylmethyl-piperidinium) and poly(p-terphenyl N - methyl-N -benzyl-piperidinium) were evaluated as hydroxide exchange membranes. The evaluated polymers displayed OH− conductivities of over 100 mS cm−1 but poor alkaline stability and high water uptake. The properties that the evaluated polymers displayed related to the size and structure of the extender group.