Proton exchange membrane fuel cells (PEMFC) have attracted considerable research interest for its advantages in cleaning energy such as no pollution and no warm house gas.Although the mostly investigated Nafion series products possess excellent properties

their low conductivity at high temperature and low humidity as well as their high cost is still limiting their application.In this work

a series of poly(vinylidine fluorde-co-trifluroethyleneco-chlorotriflurethylene)-g-sulfonated polystyrene P(VDF-co-TrFE-co-CTFE)-gSPS) copolymers with tunable graft densities and branch lengths are synthesized using commercial P(VDF-co-CTFE) via a route including partial hydrogenation

ATRP and sulfonation reaction.The structure and properties of these polymers are carefully characterized with NMR

TEM

water uptake and proton conductivity measurement.The influence of test condition and polymer construction on their properties has been well discussed.It has been shown that the graft density governs the phase separation of the resultant polymer

and therefore its water uptake and proton conductivity.The copolymer with low graft densities shows larger scale phase separation

higher water uptake and larger conductivity at low temperature.As temperature increases

the proton conductivity of the copolymer with low graft density increases.The copolymer with optimized composition exhibits even higher proton conductivity than that of Nafion-112 tested at a relative humidity over 50% in the same condition

temperature range 30~120℃.Therefore

it is expected to be an excellent PEM materials with low cost.