(92h) Effect of Block Composition on the Morphology, Hydration and Transport Properties of Sulfonated PS-b-Pegpem-b-PS

This work discusses the effect of block composition on the properties of proton conducting polymer membranes. The starting block contained poly (ethylene glycol phenyl ether methacrylate) bifunctional macroinitiator. Polystyrene was added to both sides of the block using atom transfer radical polymerization. Two different percentages of polystyrene (18% and 31%) were synthesized. These copolymers and the homopolymer were completely sulfonated. The resulting polymers produced different water absorption values and transport properties for direct methanol fuel cell (DMFC) applications. The nanostructure and morphology of the casted membranes were studied using small angle x-ray scattering and atomic force microscopy. The results revealed that all six membranes exhibited a disordered phase-segregated morphology, which changed upon sulfonation into small-interconnected ionic domains. Normalized DMFC selectivities (proton conductivity over methanol permeability divided by the respective values for NafionÒ) were calculated and ranged from 1.16 to 15.30, indicating that the performance of these materials can be comparable or better than NafionÒ. Transport property results also suggest that chemistry (block nature and composition), morphology and water content play a critical role in the transport mechanism of protons and methanol. For example, the block copolymer with 18% percent polystyrene displays shorter interstitial ionic distances and sufficient water content to produce high proton conductivity, while maintaining low methanol permeability in a multi-ionic proton exchange membrane.