Glycidyl methacrylate-ethylene dimethacrylate (GMA-EDMA) copolymer particles were synthesized by both conventional suspension polymerization and a two-step swelling technique. Oxirane groups in the products were modified by reaction with a mixture of 2,2,6,6-tetramethyl-4-aminopiperidine and its 1-oxyl paramagnetic derivative. The characteristics of the synthesized copolymer particles and the modified oxirane groups were studied with respect to the type of synthesis and the type and content of diluent.