AbstractDiallyl phthalate (DAP) was copolymerized with dialkyl fumarates, including diethyl fumarate (DEF), di‐n‐butyl fumarate (DBF), and di‐n‐octyl fumarate (DOF) by using 2,2′‐azobisisobutyronitrile as an initiator at 60°C. Both rate and degree of copolymerization were quite enhanced compared with the homopolymerization of DAP and the maximum rate was found at the molar ratio of 1:1 in the monomer feed. The cyclization of DAP was almost exclusively suppressed in the Copolymerization. Gelation was promoted from 25% of the gel‐point conversion for the DAP homopolymerization to 9% of the minimum one observed. Copolymerizability of DAP (M1) with dialkyl fumarates (M2) was quite high, with the following monomer reactivity ratios M2,r1,r2: DEF, 0.01, 1.25; DBF, 0.02, 1.01; DOF, 0.02, 0.96. These results are discussed in mech