“Synthesis and Properties of Ionic Poly(arylene ether)s for Applications in Water
Judy S. Riffle – Macromolecules and Interfaces Institute, Virginia Tech, Blacksburg, Virginia, U.S.A.
Sulfonated poly(arylene ether)s are a class of engineering polymers that form ideal membranes for transporting protons and other cations for electrodialysis, electrolysis of water and for proton exchange membrane fuel cells. Sulfonated polysulfones with controlled distributions of sulfonate ions along the chains have been synthesized by post-sulfonation and by directly polymerizing pre-sulfonated aromatic monomers. We have prepared sets of these materials with systematically varied degrees of sulfonation, and with different architectures to study inter-relationships among their compositions, interactions with water, morphologies and transport phenomena. Linear statistical and block copolymers as well as crosslinked statistical copolymers that are saturated with water are under study. The state(s) of the water in these systems have been investigated using a combination of techniques including differential scanning calorimetry, thermo-gravimetric analyses, and proton NMR methods to measure relaxations and diffusion. The equilibrium uptake of water and the nature of the water molecules, bound to the polymer versus free water, vary substantially with the density of sulfonate groups and the copolymer morphology. In the linear statistical copolymers, as the degree of sulfonation is increased, a transition in the nature of the water from bound to a combination of bound and free water occurs. In the block copolymers the diffusion rates of the free water correlate with the lengths of the blocks and hence the phase separation.
“Gas and Water Vapor Transport in Sulfonyl-Containing Polybenzimidazoles for Gas Separations
Benny D. Freeman and Donald R. Paul – McKetta Department of Chemical Engineering, The University of Texas at Austin, Texas
Due to their high chemical and thermal stability, polybenzimidazoles (PBIs) are promising candidates for use as gas separation membranes for high temperature applications, such as pre-combustion carbon capture. A series of sulfonyl-containing PBIs based on the 3,3’,4,4’-tetraaminodiphenylsulfone (TADPS) monomer were recently synthesized. In this presentation, their gas transport properties are compared to those of commercial PBI (CelazoleTM).
CelazoleTM and TADPS-based PBIs are hydrophilic, relative to most gas separation polymers used today, and some of these materials can absorb up to 25% water by mass at room temperature. Due to the potential effects of water uptake on both mechanical and gas transport properties, we also seek to understand fundamentals of interactions between water and PBIs. Water vapor gravimetric sorption and dilation measurements have been performed at 35 °C, and a significant hysteresis was observed during desorption experiments, due to swelling and plasticization. The specific volume of the water-polymer mixture as well as the partial molar volume of water in the glassy polymer have also been calculated. Furthermore, a separate FTIR analysis showed strong hydrogen-bonding interactions between water molecules and the PBI backbone.