No description available.

No description available.

No description available.

The covalent bond formed between a N-heterocyclic carbene and an aryl-isothiocyanate was discovered to be thermally-reversible. This bond was incorporated into the backbone of an aromatic polymer which, when subjected to heat and excess monomer, would depolymerize to smaller oligomers. In addition these small molecules contain active chain ends and could be repolymerized to reform the original polymer. The high molecular weight material was made into freestanding sheets with desirable mechanical properties and could be made conductive by treatment with iodine. A new poly(triazene) was formed from the reaction of a facially opposed, annulated, bis-N-heterocyclic carbene (NHC) and an organic bis-azide. The NHC as well as the azide were varied and combined to produce a series of polymers which were characterized by GPC, TGA, and NMR. These thermally robust polymers were also coated onto glass slides and rendered electrically conductive by exposure to iodine vapor. A new reagent for Reversible Addition Fragmentation Chain Transfer Polymerization (RAFT) is described. This imidazolium based reagent shows unusually fast kinetics which allows it to control polymerizations at significantly reduced loadings compared to the more traditional neutral dithiocarbamates or dithioesters. The fast kinetics is explained by the rapid rotation of the dithioester about the plane of the cationic N-heterocycle. Sulfonated poly(ether ether ketone) (sPEEK) membranes were blended with imidazoles with varying pKas. The proton conductivity of the membranes was evaluated as a function of pKa and temperature. Interestingly, the conductivity of the dry membranes showed a non-monotonous profile over a temperature range of 25 – 150 C. We use a theoretical model to better understand the mechanistic origins of the observed temperature–conductivity profiles. This model is based on the reaction equilibria between sPEEK’s sulfonic acid groups and the basic sites of the added heterocycles. Using the copper-catalyzed 1,3-dipolar “click” cycloaddition reaction, poly(sulfone)s containing pendant azide moieties were functionalized with various amounts of sodium 3-(prop-2-ynyloxy)propane-1-sulfonate and crosslinked with 1,7-octadiyne. The degree of sulfonation as well as the degree of cross-linking was systematically varied by changing the ratios of the aforementioned reagents. The polymers were cast into membranes, acidified, and then tested for proton conductivity, methanol permeability, and membrane-electrode assembly (MEA) performance. / text

Proton conducting membranes are a key component in fuel cell designs. Properties like proton conductivity, water uptake, ion exchange capacity and physiochemical stability dictate the performance and longevity of the complete fuel cell system. Designing a proton conductiting membrane takes several factors, such as monomer choice and their respective functionalization into account. Besides that, economically favourable reactions as well as environmental compability have to be considered. This work demonstrates the development of a fuel cell membrane material starting from broadly available, cost-efficient educts. Few reaction steps, also including cost-efficient reagents, have been employed in order to obtain a doubly sulfonated monomer based on naphthalene-1,5-disulfonic acid (Armstrong´s acid) suitable for polymerizations. Suzuki polycondensation of the given monomer partly yielded processable films for further investigation. A cost-efficient, atom-economic deprotection stategy was developed for sulfonated polyphenylenes, yielding proton conducting membranes. Further modification of the backbone structure, by incorporating an excess of hydrophobic meta,meta,meta-terphenylene units, led towards balanced properties of the material. The impact of polymer constitution, was investigated and discussed via the implementation of para,meta,para-substituted instead of meta,meta,meta-substituted terphenylene. Alternating and statistical copolymers including para,meta,para-substituted terphenylene were developed and investigated. The reported proton conducting membranes pose suitable and promising candidates for fuel cell applications.