Block copolymers of cyclohexene oxide (CHO) and ketonic resin were prepared by using ketonic resins as free radical pholoinitiators via two-step procedure. hi the first step, cyclohexanone-formaldehyde and acetophenone-formaldehyde resins were modified during their preparation with benzoin and benzoin isobutyl ether. Then, AB or ABA type block copolymers depending on the resin employed were obtained by irradiation of these resins in the presence of pyridinium salt and CHO as a cationically polymerizable monomer. By this way, block copolymers of CHO with ketonic resin were prepared and characterized by GPC, DCS, FTIR, and H-1 NMR spectral measurements. (c) 2007 Wiley Periodicals, Inc.