Photocuring and Photolithography of Proton-Conducting Polymers Bearing Weak and Strong Acids

A series of novel conformable proton-conducting thin films has been prepared from photocurable liquid polyelectrolytes. Films prepared in such a fashion show promise for engineering unconventionally shaped proton-exchange membranes using photolithographic techniques. These films are semi-interpenetrating networks (semi-IPN) comprising a linear proton-conducting guest polymer, sulfonated poly[ether ether ketone] (S-PEEK), in the presence of a statistically cross-linked host polymer matrix comprising divinyl sulfone, vinylphosphonic acid, and acrylonitrile. Film properties ranging from brittle and fragile to robust and flexible have been obtained, depending on the ratio of host/guest composition used. The extent of dissociation of the weak acid component, vinylphosphonic acid, is strongly dependent on the S-PEEK content. Proton conductivity, water content, and lambda values are dependent on the membrane composition and degree of cross-linking. Proton conductivities similar to those of pure S-PEEK, ∼0.07 S/cm, have been observed for a semi-IPN containing as little as 35 wt % S-PEEK.