KEY WORDSTriallyl Isocyanurate / Diallyl Terephthalate / Steric Effect / Intermolecular Crosslinking / Thermodynamic Excluded Volume Effect / Molecular Weight Distribution / As part of our continuing studies concerned with the free-radical polymerizations of multiallyl compounds in terms of allyl polymerization, cyclopolymerization, and gelation, 1-3 we have been concerned with the elucidation of the specific polymerization behavior of triallyl isocyanurate (TAIC), especially focusing on the steric effect caused by the bulky isocyanurate side groups. 4-9 Thus, it was found by chance that the primary chain length of the TAIC polymer is quite high compared with the polymerization of its isomer triallyl cyanurate (TAC), being ascribed to the reduced monomer chain transfer (degradative chain transfer characteristic of allyl polymerization) 10 due to the steric effect by the bulky isocyanurate side groups on transition state formation. 4 This steric effect is further discussed by both the copolymerization with allyl benzoate and the telomerization in the presence of CBr 4 , 5 by the polymerization of diallyl alkyl isocyanurates, 6 by the polymerization and copolymerization of trimethallyl isocyanurate and trimethallyl cyanurate, 7 and by the copolymerization with sterically unhindered monomers. 8 In particular, the last two papers 7, 8 are concerned with the discussion of the steric effect on the reactivity of growing polymer radical in terms of the sequence length dependence of the sterically bulky TAIC units. This is extended to the non-terminal units effect on the cyclopolymerization of TAIC. 9 As our further pursuit of the specific polymerization behavior of TAIC in comparison with other multiallyl compounds, the molecular-weight distribution (MWD) curves of resulting prepolymers were examined by using size-exclusion chromatography (SEC) equipped † To whom correspondence should be addressed.with a multiangle laser light scattering (MALLS) device (SEC-MALLS) in order to explore in more detail the occurrence of intermolecular crosslinking reaction. Here it is worthwhile to note that SEC is commonly used to determine the molecular weight and the MWD of resulting prepolymers. However, as a technique it is not always applicable to our crosslinking polymerization systems because the structure of prepolymer changes from a linear to a branched form with progressing polymerization. On the other hand, SEC-MALLS is expected to be a very useful and efficient tool in characterizing our prepolymers because the use of MALLS, as an absolute detector, enables the molecular weight and MWD to be determined directly without any calibration. 11 Thus, this article deals with the further discussion of the specific polymerization behavior of TAIC; the occurrence of intermolecular crosslinking reaction was explored in detail as compared with the polymerization behavior of diallyl terephthalate (DAT) as a typical multiallyl compound. In the polymerization of TAIC, the conversion dependence of the MWD profiles of resulting prepolymers was ...