The effect of network structure on the physical and electrical properties of polymers can be usefully probed with materials that have novel, well-defined structures. We are investigating such materials including double network elastomers (in which an initial network is deformed prior to further crosslinking), networks of miscible polymer blends (especially interesting when the components have very different degrees of crosslinking), and networks having a combination of covalent and ionic bonds. Mechanical and electromechanical measurements, dielectric spectroscopy, and optical birefringence are employed. Our efforts focus on developing new materials with novel properties.