Lina Karlsson

Sulfophenylation of polysulfones for proton-conducting fuel cell membranes

Polysulfone has been sulfophenylated by lithiation and anionic reaction with 2-sulfobenzoic acid cyclic anhydride. This provides a new convenient method to modify polysulfones by attaching pendant sulfonated phenyl groups via ketone links. Membranes of the sulfophenylated polysulfones show promise for use in proton-exchange-membrane fuel cells. For example, a membrane with 0.9 sulfophenyl units per repeating polysulfone unit and 30 wt.-% water was found to have a proton conductivity of 32 mS/cm at 60degreesC.

Water absorption and proton conductivity of sulfonated acrylamide copolymers

Copolymers of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and N-tert-butylacrylamide (tBAA) have been evaluated as proton conducting materials. The water absorption of copolymers with varying equivalent weights (EW), i.e. g polymer/mol sulfonic acid groups, was studied at different relative humidities (rh) by gravimetry and calorimetry. Melt endotherms for water were detected by DSC in copolymers containing greater than or equal to 45 mol% AMPS when equilibrated at 93% rh, and greater than or equal to 36 mol% AMPS when equilibrated at 98% rh. A study of the kinetics of the water absorption at 98% rh showed that equilibration was faster for the copolymers than for the homopolymer PAMPS. The proton conductivity (Q) of the samples was investigated as a function of temperature, water content, and EW. ac Impedance measurements between -20 and 70 degreesC showed a value of sigma as high as 0.2 S/cm at 70 degreesC for a copolymer containing 54 mol% AMPS equilibrated at 98% rh. It was concluded that both the EW and the amount of water in the polymers controlled the conductivity at all temperatures. For example, increasing amounts of water in the polymers generally gave increasing sigma above the melting point of the water, but decreasing Q below the same temperature. (Less)

Preparation and solution properties of amphiphilic sulfonated acrylamide copolymers

Copolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and N-tert-butylacryl-amide has been carried out in methanol at 60degreesC using AIBN as initiator. Both IR and H-1 NMR spectroscopy indicated that monomer conversions exceeding 95% were reached in the copolymerizations. Copolymers containing more or equal to approximate to 15 mol-% AMPS were soluble in water and had an amphiphilic character. Analysis by dilute solution viscometry, quasi-elastic light scattering, and size exclusion chromatography in water and aqueous KCl solution showed that the AMPS homopolymer and the copolymers behave as polyelectrolytes. Light scattering analysis and atomic force microscopy indicated the presence of aggregates in aqueous solutions of a copolymer containing 15 mol-% AMPS. Gravimetrical measurements showed that the water absorption of the copolymers in humidified air increases almost linearly with the AMPS content of the copolymers.

Controlling structure in associating polymer-surfactant mixtures

Structures of concentrated mixtures of associating polymer-surfactant mixtures are important in many technical applications. Yet an in-depth understanding of how molecular parameters affect these structures is lacking. We here summarize the results of ongoing work using a novel simplified approach to the study of associating oppositely charged polymer-surfactant mixtures, introducing a minimum number of components to the various mixtures. The results illustrate the relations between systems with and without polyions, as well as effects of systematic changes of parameters such as surfactant chain length, polyion length, polyion charge density, and the charge density of the surfactant aggregate.