This study involved the investigation of morphological changes in ion exchanger catalysts after more than 12 years in an industrial reactor for esterification of acrylic acid with methanol. The results showed that both desulfonation and de/crosslinking of the polymer was quite extensive. These changes were detected to a higher extent in test polymer samples located near the reactor input than in the sample obtained from main reactor charge, indicating that impurities in the reaction mixture, probably peroxidic compounds, could be responsible for the splitting of C-S and C-C bonds.