(99g) Design Of Nanoporous, Proton-Conductive Polymer Thermosets

In this work, we focus on the synthesis and characterization of copolymer membranes exhibiting tunable nanoscopic porosity, high proton conductivity as well as being mechanically stable. Materials possessing high ion conductivity are finding importance as membranes for fuel cell and battery membranes and our approach of utilizing cross-linked hydrophobic and hydrophilic copolymers membranes is an interesting way to design such materials.

We have investigated a novel system consisting of free radically copolymerized, hydrophobic, difunctional DGEBA vinyl ester (VE) and hydrophilic, monofunctional 2-acrylamido 2-methyl 1-propane sulfonic acid (AMPS) in a common diluent, dimethyl formamide (DMF). The solvent also acts as a porogen and induces porosity via solvent extraction using supercritical carbon dioxide with pore sizes of about 50nm. Experimental results show that mechanically stable membranes with conductivities of 0.0346 S/cm, exceeding that of Nafion® 117, and having glass transition temperatures above 120°C have been realized. Correlations between the pore size/porosity versus the water uptakes and conductivities have been identified as well. It has been determined that although the ionogenic (and hydrophilic) nature influences the water uptake and mechanical properties of these membranes, porosity is also a factor contributing to artificially altered water uptakes and is a relevant and tunable parameter in membrane design. The reaction kinetics in this system have been investigated to qualitatively determine the microstructure of the formed copolymer. Results suggest evidence of greater homopolymerization of VE as compared to AMPS resulting in a predominantly VE backbone structure with interspersed AMPS moieties. The properties of these novel polymer networks and the influence of nanoscale structure on these properties will be discussed in detail.