A series ionomers of sulfonated ethylene-propylene copolymers containing -SO3Na group from 0 to 12. 0 mol% have been prepared by hydrolysis of chlorosulfonated copolymers. Three methods were used for analysis of sulfur and chlorine contents in ionomers. Decrease in crystallinity for ionomers with increase in -SO3Na group concentration was showed by DSC and WAXD curves. The ionic peak in the LAXD curves and the marked increase of T

with ion concentration were observed only for ionomers sulfonated above 5-7 mol%. These facts were considered to be evidences for the existence of ionic clusters in sulfonated above the critical concentration.