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Structure, Property and Cure Kinetics of Thermosetting Copolymers

Mohamed Aflal and Giuseppe R. Palmese. Department of Chemical and Biological Engineering, Drexel University, 3141 Chestnut St., CAT 471, Philadelphia, PA 19104

In this work, we focus on the synthesis and characterization of multifunctional copolymer membranes exhibiting high ion conductivity as well as thermo-mechanical strength with an added parameter of tunable nanoscopic porosity. Materials possessing high ion conductivity are finding importance in material systems for fuel cell and battery membranes and our approach of utilizing cross-linked hydrophobic and hydrophilic copolymers membranes is one approach towards the rationalistic design of such high-performance 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 potogen and induces nanoscale porosity via solvent extraction using supercritical carbon dioxide. Characterization has been done using AC Impedance Spectroscopy, water uptake studies and dynamic mechanical analyses, and pore size analysis by microscopy. Mechanically stable membranes with conductivities of 0.0346 S/cm, exceeding that of NafionŽ 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 in these membranes, porosity is a factor contributing to artificially altered water uptakes and is a relevant and tunable parameter in membrane design. The cure kinetics in this system has 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.