Polymer electrolyte compositions having polymerized monomer units of the structural formula: ##SPC1##Or acidic or alkaline salts of these compositions. R.sub.1 and R.sub.2 are hydrogen, methyl or ethyl. Also disclosed are methods for producing these compositions by reacting .beta.-propiolactone and a polymer composition including vinylpyridine monomer units, by hydrolyzing a neutral salt of the above structural formula to obtain a N-(2-carboxyethyl) poly- .gamma. -vinylpyridine acidic or alkaline salt, by reacting the N-(2-carboxyethyl) poly- .gamma. -vinyl-pyridine salt with an acid or alkali to form a corresponding acid, neutral or alkaline salt, and by reacting a diluted or weak acid or alkali under nonhydrolyzing conditions with a polymer of the above structural formula to form a corresponding acidic, neutral or basic salt.