A novel series of polyphosphazene-graft-polystyrene (PP-

g

-PS) copolymers were successfully prepared by atom transfer radical polymerization (ATRP) of styrene monomers and brominated poly(bis(4-methylphenoxy)phosphazene) macroinitiator. The graft density and the graft length could be regulated by changing the bromination degree of the macroinitiator and the ATRP reaction time

respectively. The PP-

g

-PS copolymers readily underwent a regioselective sulfonation reaction

which occurred preferentially at the polystyrene sites

producing the sulfonated PP-

g

-PS copolymers with a range of ion exchange capacities. The resulting sulfonated PP-

g

-PS membranes prepared by solution casting showed high water uptake

low water swelling and considerable proton conductivity. They also exhibited good oxidative stability and high resistance to methanol crossover. Morphological studies of the membranes by transmission electron microscopy showed clear nanophase-separated structures resulted from hydrophobic polyphosphazene backbone and hydrophilic polystyrene sulfonic acid segments

indicating the formation of proton transferring tunnels. Therefore

these sulfonated copolymers may be candidate materials for proton exchange membranes in direct methanol fuel cell (DMFC) applications.