Solid Polymer Electrolytes Based on Ionic Graft Polymers: Effect of Graft Chain Length on Nano-Structured, Ionic Networks

• Published in: Advanced functional materials 2002-05, Vol.12 (5), p.389-394
• Main Authors: Ding, J., Chuy, C., Holdcroft, S.
• Format: Article
• Language: English
• Subjects: Fuel cells; Graft polymers; Polystyrene sulfonates (PSS); Solid polymer electrolytes
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/1616-3028(20020517)12:5<389::AID-ADFM389>3.0.CO;2-5

The length of graft chains in graft polymers is controlled in order to dictate the formation of a nanochannel network of ions in a non‐ionic matrix. Graft polymers were prepared by copolymerization of styrene with poly(sodium styrene sulfonate) (PSSNa) macromonomers. The latter were prepared with controlled molecular weight and narrow polydispersity by stable free radical polymerization. Phase separation of ionic aggregates occurs to a greater extent in films prepared from amphiphilic polymers possessing longer graft chains. Films prepared from polymers containing low ion content comprise of isolated ionic domains and exhibit low ionic conductivity. Increasing the ion content with the membrane, by increasing the number density of ionic graft chains in the polymer, results in ionic domains that coalesce into a network of nanochannels, and a dramatic increase in ion conductivity is observed. The ionic network is developed to a greater extent for films based on longer ionic graft chain polymers; an observation explained on the basis of phase separation. Highly conductive polystyrene sulfonate films containing a high density of ionic graft chains (see Figure) consist of ionic domains that coalesce into a network of nanochannels. These ionic graft membranes show various degrees of phase separation, whereby the extent of phase separation affects the water sorption and ionic conductivity. The polymers obtained provide fundamental information regarding the design and properties of solid polymer electrolytes.