NOVELTY - Making the proton conducting polymer electrolyte comprising a proton conducting ionomer and an amount of a copolymer comprising crosslinking functional groups and other functional groups, comprises mixing the copolymer with the proton conducting ionomer, and heating the mixture such that the copolymer bonds to the proton conducting ionomer, where the proton conducting ionomer and the copolymer are covalently bonded or acid-base complexed together at the crosslinking functional groups of the copolymer.    USE - The proton conducting polymer electrolyte is useful in solid polymer electrolyte fuel cells.    ADVANTAGE - The method provides proton conducting polymer electrolyte with improved durability, mechanical and chemical properties and fuel cell performance.    DETAILED DESCRIPTION - Making the proton conducting polymer electrolyte comprising a proton conducting ionomer and a copolymer comprising crosslinking functional groups and other functional groups, comprises mixing the copolymer with the proton conducting ionomer, and heating the mixture such that the copolymer bonds to the proton conducting ionomer, where the proton conducting ionomer and the copolymer are covalently bonded or acid-base complexed together at the crosslinking functional groups of the copolymer, the copolymer comprises a polymerized network of metal oxide monomers with crosslinking functional groups and metal oxide monomers with other functional groups in random or block sequence, the polymerized network is characterized by an alternating series of oxygen and metal bonds, the metal oxide monomers with crosslinking functional groups comprise a first metal bonded to at least two oxygen atoms and comprising silicon (Si), titanium (Ti), zirconium (Zr), cerium (Ce), tantalum (Ta), and chromium (Cr) and crosslinking functional groups bonded to the first metal and comprising a functional end group containing nitrogen or oxygen and having amine (-NH2), imine (=NH), -(aliphatic)-OH, -(aryl)-OH, pyrimidinyl, pyrazinyl, (1,2,4)triazinyl, (1,2,4,5)tetrazinyl, pyridazinyl, 1-methyl-piperidinyl, pyridinyl, 1,4-dimethyl-piperazinyl, 2-methyl-oxazole group of formula (A) and 2-methyl-1H-imidazole group of formula (B), and the metal oxide monomers with other functional groups comprise a second metal bonded to at least two oxygen atoms and consisting of Si, Ti, Zr, Ce, Ta, and Cr, and other functional groups bonded to the second metal and consisting of proton carrier functional groups comprising a functional end group of formula -PO3H2, -COON, -SO3H or -SO2NHSO2CF3, metal chelating functional groups comprising a functional end group consisting of phosphonic acid, bipyridine, phenanthroline and their derivatives, and free radical scavenger functional groups comprising a functional end group consisting of aminophenyl, hydroxyphenyl and their derivatives.    R = hydrocarbon.