Radical polymerizations of triallyl isocyanurate (TALC) and its isomer triallyl cyanurate (TAC) were conducted in benzene at 60 Β°. In the polymerization of TALC, gelation occurred quite early and the primary chain length was quite high compared with that for TAC. Both TAlC and TAC were copolymerized in bulk with allyl benzoate (ABz); the primary chain length decreased markedly with increase in the mole fraction of ABz and the difference between TAIC and TAC copolymerizations was reduced until almost no difference was observed above 50 moi% of ABz. Gelation was delayed with increasing ABz in the feed and the gel points for both TAIC and TAC copolymerizations were reached at the same conversions above 50 reel% ABz. The telomerization behaviours of TAIC and TAC in the presence of CBr4 were explored; the difference between TAIC and TAC polymerizations was significantly reduced as monomer chain transfer was replaced by chain transfer to CBr4. The chain transfer constant Ccsr, was estimated to be 77 and 84 for TAIC and TAC, respectively. These results are discussed in connection with a steric effect in the radical polymerization of TAIC leading to increased chain length.