Abstract: The present invention provides polymer electrolyte membranes (PEM) based upon sulfonated poly 2-(phenyl ethyl)siloxane (SPPES) prepared in a one-pot procedure. This includes the SPPES homopolymer as well as random copolymer of SPPES with various non-sulfonated polysiloxanes. Copolymerization with poly 2-(phenyl ethyl)siloxane greatly improves the mechanical stability of the film compared to a SPPES homopolymer. Proton conductivity of the copolymer, though it is less than that of the homopolymer and Nafion, is comparable to other PEMs in the literature. Both SPPES based membranes show good water retention at temperature greater than 100° C., which indicates they may be suitable for use in high temperature PEM fuel cells.