Radiation curable printing ink composition

The invention is a radiation curable printing ink composition comprising a liquid viscous epoxidized diene polymer and a pigment. Preferred diene polymers are block copolymers comprising at least interior and exterior diene blocks wherein the exterior diene blocks contain a greater concentration of di-, tri-, and tetrasubstituted olefinic epoxides than the interior blocks and wherein the copolymer contains from 0.1 to 3.0 Meq of olefinic epoxides per gram of copolymer and the peak molecular weights as determined by gel permeation chromatography of the exterior blocks of from 300 to 2000 and the peak molecular weights as determined by gel permeation chromatography of the interior blocks are from 2,000 to 10,000. In another preferred embodiment, the polymer is a star polymer having a random distribution of from 0.5 to 5 Meq of di-, tri-, and tetrasubstituted olefinic epoxides per gram of polymer and greater than four arms wherein the peak molecular weights as determined by gel permeation chromatography of the arms are from 1500 to 15,000.