Block copolymers of cyclohexanone-formaldehyde resin (CF-resin) and polystyrene and graft copolymers of styrene on ethyl cellulose, respectively, were prepared via peroxycarbamates. NCO/OH ratio was the important parameter during preparation of polymeric peroxycarbamates from prepolymeric isocyanate-terminated peroxycarbamates and CF-resin. Cross-linked copolymers were produced if NCO/OH ratio was above 2:9. Ethyl cellulose with low hydroxy value was used as hydroxy compound for the preparation of peroxycarbamate. About one of every two anhydroglucose units of ethyl cellulose was grafted with polystyrene.