Cyclopolymerization of triallyl isocyanurate (TAIC) as compared with its isomer triallyl cyanurate (TAC) is discussed in terms of the nonterminal units effect caused by the sterically bulky isocyanurate side groups. Thus, the monomer concentration dependence of the: initial residual unsaturation is not explained by considering an ordinary cyclopolymerization mechanism, although TAC polymerization obeyed the mechanism. The effect of the forced introduction of bulkier noncyclic units into the polymer chain on the cyclopolymerizability of TAIC was explored by the copolymerization with allyl dibenzyl isocyanurate, resulting in the enhanced cyclization in conformity with our expectation. (C) 2000 Elsevier Science Ltd. All rights reserved.