Proton conducting membranes consisting of poly(vinyl alcohol) and poly(styrene sulfonic acid): Crosslinking of poly(vinyl alcohol) with and without succinic acid

• Thermal treatment of PVA-polysulfonic acid composite to give (CHCH)n− in the PVA main chain
• Thermal treatment of PVA-polysulfonic acid composite to cause self-crosslinking of PVA
• Self-crosslinking of PVA by addition of OH to (CHCH)n−
• Crosslinking of PVA by succinic acid
• Insolubilized PVA-polysulfonic acid film with σ of 10− 1 S cm− 1

Preparation of proton conducting PVA-PSS polymer films composed of cross-linked poly(vinyl alcohol) (PVA) and poly(styrene sulfonic acid) (PSS) is described. The PVA-PSS film was insolubilized in hot water by the crosslinking reaction with succinic acid (SA) in a temperature range of 180–200 °C. Insolubilization of the PVA-PSS film in hot water was also achieved by self-crosslinking that occurred in the PVA-PSS system in a temperature range of 130–180 °C, even in the absence of SA. This self-crosslinking in the PVA-PSS system is thought to proceed via PSS-catalyzed dehydration of PVA to form olefinic CHCH − units and ethereal O − units. Coloring of the PVA-PSS film to black by thermal treatment supported the formation of π-conjugated (CHCH)n− units. Both the PVA-PSS-SA and PVA-PSS films showed proton conductivity of approximately σ = 0.1 S cm− 1 at 80 °C and 95% relative humidity. The self-crosslinking observed with the PVA-PSS system was followed by gravimetry.